CURB-65 and PSI: pneumonia severity scoring and risk stratification · ICU Topics

Cinematic ICU scene of a chest X-ray showing bilateral consolidation on the screen, a CURB-65 and PSI scoring sheet on a clipboard, a calculator showing the mortality risk, clinical-blue lighting, medical educational, no faces, no text — FigureThe severity scores for the community-acquired pneumonia — the CURB-65 (the confusion, the urea, the respiratory rate, the blood pressure, the age over 65) for the bedside, the PSI for the precision. The CURB-65 of 3 or more is the hospital and the ICU consideration; the PSI class IV to V is the admission.

Why severity scoring matters

Pneumonia severity scores serve three distinct purposes, and conflating them leads to wrong decisions: [1]

Mortality prediction (PSI best validated; CURB-65 simpler proxy) — answers "how likely is this patient to die?"
Site-of-care decision (CURB-65, PSI, CRB-65) — outpatient vs inpatient vs ICU.
ICU support prediction (IDSA/ATS, SMART-COP) — will this patient need ventilation or vasopressors? [1]

A score that predicts mortality does not necessarily predict ICU need. This is why guideline bodies recommend using MORE THAN ONE score: CURB-65 or PSI for outpatient/inpatient triage, plus IDSA/ATS or SMART-COP for ICU triage. [1]

Epidemiology: CAP is the most common infectious cause of death in the developed world. Mortality: outpatient ~1%, ward ~5-10%, ICU ~20-50%. Roughly 10-20% of CAP requires hospitalisation; 10-20% of those need ICU. Site-of-care decisions directly affect outcome — both under-triage (ward patient crashes) and over-triage (ICU bed waste, nosocomial risk) are harmful. [1]

The cardinal error: treating any score as a replacement for clinical assessment. Scores miss approximately 10-25% of patients who actually need ICU (false negatives), particularly young patients and those with physiological decompensation not captured by static single-time-point variables. [1]

CURB-65 — detailed scoring and interpretation

CURB-65 components: confusion, urea, respiratory rate, blood pressure, age over 65 with mortality risk bands — FigureCURB-65 — five bedside items; score ≥3 prompts hospital/ICU consideration with clinical judgment.

Components (each = 1 point, total 0-5):

Confusion — new-onset disorientation in person, place, or time (or AMTS ≤8/10). Pre-existing dementia counts only if worse than baseline.
Urea >7 mmol/L (BUN ≥20 mg/dL) — marker of dehydration and renal dysfunction.
Respiratory rate ≥30/min — measure over a full 60 seconds (counting for 15 s × 4 underestimates paradoxical/irregular breathing).
Blood pressure: SBP <90 mmHg OR DBP ≤60 mmHg.
65: age ≥65 years. [1]

Worked example 1: A 72-year-old nursing home resident with confusion, RR 32, BP 96/55, urea 9.5 mmol/L → CURB-65 = 5 (all five positive). Mortality risk ~57% → ICU. [1]

Worked example 2: A 38-year-old with RR 28, BP 110/70, urea 6, no confusion → CURB-65 = 0. Looks low-risk — but if SpO2 is 88% on room air with PaO2/FiO2 180, this patient has severe hypoxia NOT captured by CURB-65. Use IDSA/ATS criteria instead. [1]

Worked example 3: A 70-year-old with confusion and urea 9 but RR 24, BP 120/80 → CURB-65 = 3 (age, confusion, urea). Mortality ~14.5% → inpatient, consider ICU. The high score is driven by age — without being 70, the score would be 2. This illustrates the age-weighting problem. [1]

Pneumonia severity scores compared

Score	Variables	Best for	Strengths	Weaknesses
CURB-65	5 simple bedside	Rapid triage, ED	Simple, memorable, fast	Underestimates young patients; age-weighted
PSI (PORT)	20 (demographics, comorbidity, exam, labs, CXR)	Mortality prediction	Most validated; sensitive	Complex; requires calculation; lab-dependent
IDSA/ATS	9 minor + 2 major criteria	ICU admission decision	Gold standard for severe CAP; specific	May under-triage young; lab-dependent
SMART-COP	8 (systolic BP, multilobar CXR, albumin, RR, age, neutrophils, platelets, urea)	Predicts IRVS (ventilator/vasopressor)	Better for identifying who needs ICU support	Less widely used outside ANZ
CRB-65	4 (CURB-65 without urea — no labs)	Primary care (no bloods)	No lab needed	Less sensitive than CURB-65

[1]

CURB-65 — mortality and disposition by score

Score	Components positive	30-day mortality	Recommended disposition
0	None	0.7%	Outpatient (home)
1	One	2.1%	Outpatient (home)
2	Two	9.2%	Inpatient (ward) — consider brief inpatient or observation
3	Three	14.5%	Inpatient — consider ICU
4	Four	40%	ICU
5	All five	57%	ICU

[1]

PSI (PORT) — risk classes and mortality

Class	Definition	Mortality	Recommended site of care
I	Age <50, no predictors, normal exam/labs	0.1%	Outpatient
II	≤70 points	0.6%	Outpatient
III	71-90 points	0.9%	Observation / brief inpatient
IV	91-130 points	9.3%	Inpatient (ward)
V	>130 points	27.0%	Inpatient — consider ICU

[1]

SMART-COP — IRVS risk by score

Score	IRVS (ventilator/vasopressor) need	Disposition
0-2	~5%	Ward (low risk)
3-4	~25%	Ward with close monitoring / HDU
5-6	~55%	ICU
7-8	~84%	ICU

[1]

Score-to-score comparison — strengths and weaknesses

Dimension	CURB-65	PSI (PORT)	IDSA/ATS	SMART-COP
Primary purpose	Mortality/site-of-care	Mortality prediction	ICU triage	ICU support prediction
Number of variables	5	20	9 minor + 2 major	8
Time to calculate	30 seconds	5-10 min (app needed)	2-3 min	2-3 min
Labs required	Urea only	Full panel + ABG + CXR	ABG, FBC, U&E, CXR	Albumin, ABG, creatinine, FBC
Includes oxygenation?	NO	YES (PaO2/SpO2)	YES (PaO2/FiO2)	YES (PaO2/SpO2/PF ratio)
Includes comorbidity?	NO	YES (5 conditions)	NO (implicitly)	NO
Age weighting	+1 if ≥65	Heavy (age = primary driver)	None	Inverted (age ≤50 = +1)
Young patient performance	Poor (under-triages)	Poor (under-triages)	Good	Best
Elderly patient performance	Over-triages	Over-triages	Under-detects (blunted response)	Moderate
Validated in immunocompromised?	No	No	No	No
Sensitivity for ICU need	~50%	~60%	~70%	~80%
Specificity for ICU need	~80%	~80%	~90%	~85%
International adoption	Universal	Universal	Universal (gold standard)	Predominantly ANZ
Examiner favourite	Yes (calculation)	Yes (structure)	Yes (criteria list)	Yes (ANZ context)

[1]

IDSA/ATS severe CAP criteria — ICU admission

MAJOR CRITERIA (either = severe → ICU) — (a) Invasive mechanical ventilation required (type 1 or 2 respiratory failure). (b) Septic shock requiring vasopressors (after adequate fluid resuscitation)
MINOR CRITERIA (≥3 = severe → ICU) — count the following: (1) RR ≥30 breaths/min. (2) PaO2/FiO2 ≤250 (or SpO2 ≤90% on room air). (3) Multilobar infiltrates on CXR. (4) Confusion/disorientation. (5) Urea >7 mmol/L (BUN ≥20 mg/dL). (6) Leukopenia <4 ×10⁹/L. (7) Platelets <100 ×10⁹/L. (8) Hypothermia <36°C. (9) Hypotension requiring aggressive fluid resuscitation
DECISION — ≥3 minor criteria → severe CAP → ICU admission. 1 major criterion → severe CAP → ICU. 1-2 minor → ward (monitor closely). 0 minor → consider outpatient/ward
CAVEATS — (a) These criteria are for SEVERITY/ICU triage, NOT for outpatient vs ward (use CURB-65/PSI for that). (b) Young patients may have severe pneumonia without meeting age-weighted scores — don't be falsely reassured. (c) Clinical judgement overrides — if patient looks sick (work of breathing, septic) → manage as severe regardless of score

[1]

Practical pneumonia assessment workflow

TRIAGE ASSESSMENT (first 15 minutes) — Vitals (RR over 60 s, SpO2 on room air, BP both arms, temp, GCS/AMTS). Examine: work of breathing, accessory muscle use, cyanosis, chest auscultation. Bedside tests: capillary glucose, venous/arterial blood gas, point-of-care lactate.
CALCULATE CURB-65 — 5 components, 30 seconds. Score 0-1: consider outpatient (but check oxygenation). Score 2: admit ward. Score ≥3: consider ICU/HDU.
CALCULATE PSI — if bloods and CXR available (use app/calculator). Class I-II: outpatient. Class III: observation. Class IV: ward. Class V: ICU consider.
CHECK IDSA/ATS CRITERIA — for ICU triage. Count minor criteria; check for major criteria (need MV or septic shock). ≥3 minor or 1 major → ICU.
CONSIDER SMART-COP — especially if young patient or ANZ setting. Score ≥3 → IRVS risk high.
INTEGRATE SEPSIS ASSESSMENT — qSOFA (≥2 = high risk), lactate (≥2 = hypoperfusion; ≥4 = severe sepsis), SOFA for organ dysfunction.
APPLY CLINICAL JUDGEMENT — Does the patient look sick? (Accessory muscle use, single-word dyspnoea, altered mentation, cold peripheries, oliguria). Is there trajectory of deterioration? (Serial vitals over 1-4 hours). Any score–clinical mismatch → escalate.
DECIDE SITE OF CARE — Outpatient (low all scores, good physiology, safe social situation). Ward (moderate scores, stable physiology). HDU (borderline, needs close monitoring). ICU (severe scores OR major criteria OR clinical judgement says sick).
RE-ASSESS — Static scores miss deterioration. Repeat CURB-65 and vitals at 4-8 hours. Any rise in score or deterioration in physiology → escalate.

[1]

PSI (Pneumonia Severity Index / PORT score) — detailed

Two-step calculation: [1]

Step 1 — Stratify (assign Class I if possible without points):

Men: assign points = age.
Women: assign points = age − 10.
Nursing home resident: +10 points.
If patient has NO comorbid predictors, NO adverse exam findings, NO adverse lab findings AND is in low-point range → Class I (outpatient, no further calculation needed). [1]

Step 2 — Point scoring (the 20 variables): [1]

Demographics (2):

Age: men = age in years; women = age − 10
Nursing home resident: +10 [1]

Comorbidities (5):

Neoplastic disease (any cancer except non-melanoma skin, active within 1 year): +30
Liver disease (cirrhosis, chronic active hepatitis): +20
Congestive heart failure: +10
Cerebrovascular disease (stroke, TIA): +10
Renal disease (creatinine >200 µmol/L or on dialysis): +10 [1]

Physical examination (5):

Altered mental status (confusion/disorientation): +20
RR ≥30/min: +20
SBP <90 mmHg: +20
Temperature <35°C or ≥40°C: +15
Pulse ≥125/min: +10 [1]

Laboratory and radiographic (7):

Arterial pH <7.35: +30
BUN ≥11 mmol/L (≥30 mg/dL): +20
Sodium <130 mmol/L: +20
Glucose ≥14 mmol/L (≥250 mg/dL): +10
Haematocrit <30%: +10
PaO2 <60 mmHg OR SpO2 <90%: +10
Pleural effusion on CXR: +10 [1]

Sum the points → risk class:

Class I: not assigned by points (see Step 1).
Class II: ≤70 points.
Class III: 71-90 points.
Class IV: 91-130 points.
Class V: >130 points. [1]

Strengths: most validated (Fine 1997 — 38,039 patients); most sensitive for mortality; captures comorbidity and oxygenation. [1]

Weaknesses: (1) Complex — 20 variables, requires calculator/app. (2) Lab- and radiograph-dependent — not usable in primary care or rapid ED triage. (3) Age-weighted — a young patient with severe pneumonia scores low because age dominates (a 30-year-old with septic shock and PaO2/FiO2 100 may still be Class III). (4) Sensitive but less specific — may over-admit. (5) Does not directly predict need for ventilatory/vasopressor support. [1]

Worked example: A 78-year-old nursing home man with CHF, RR 32, SBP 86, confusion, BUN 12, Na 128, PaO2 55, pH 7.30, pleural effusion.

Age 78 (male) = 78. Nursing home +10 → 88. CHF +10 → 98. Confusion +20 → 118. RR≥30 +20 → 138. SBP<90 +20 → 158. pH<7.35 +30 → 188. BUN≥11 +20 → 208. Na<130 +20 → 228. PaO2<60 +10 → 238. Pleural effusion +10 → 248 points → Class V → ICU. [1]

SMART-COP — detailed

Components (8, weighted by points):

S = Systolic BP <90 mmHg: 2 points
M = Multilobar CXR involvement: 1 point
A = Albumin <32 g/L (3.2 g/dL): 1 point
R = Respiratory rate ≥25/min (note: lower threshold than CURB-65's 30): 1 point
T = Tachycardia ≥125 OR Age ≤50 (inverted age weighting — flags young patients): 1 point
C = Creatinine >130 µmol/L (some versions: or CRP elevated): 1 point
O = Oxygen: PaO2 <70 mmHg OR SpO2 ≤93% OR PaO2/FiO2 <333: 2 points
P = Platelets <130 ×10⁹/L OR arterial pH <7.35: 1 point [1]

Interpretation — IRVS (intensive respiratory or vasopressor support) need:

0-2: low risk (~5% IRVS) → ward.
3-4: moderate (~25%) → HDU/close monitoring.
5-6: high (~55%) → ICU.
7-8: very high (~84%) → ICU. [1]

Strengths: (1) Best score for predicting need for ICU support (ventilation/vasopressors), not just mortality. (2) Inverted age weighting (Age ≤50 gains a point) — corrects the major flaw of CURB-65/PSI which under-triage young patients. (3) Includes oxygenation. (4) Validated in ANZ (Charles 2008). [1]

Weaknesses: (1) Less internationally adopted than CURB-65/PSI. (2) Requires albumin and arterial blood gas (not always available at triage). (3) Validated predominantly in ANZ populations — external generalisability less robust. [1]

CRB-65 — primary care version

Same as CURB-65 minus urea. 4 points: Confusion, RR≥30, BP<90/≤60, Age≥65.

SCORE 0: low risk → home.
SCORE 1-2: moderate → consider admission.
SCORE 3-4: high → urgent admission/hospital (consider ICU). [1]

USEFUL in primary care (GP), pre-hospital, or resource-limited settings where urea is not available. LESS sensitive than CURB-65 — if bloods available, prefer CURB-65. [1]

When to use which score — practical guidance

Practical use of CURB-65, PSI and SMART-COP for site-of-care and ICU triage decisions in community-acquired pneumonia — FigureScore selection — CURB-65 for speed, PSI for precision, SMART-COP when ICU need is the question.

When to use which score — clinical decision guide

Clinical question / setting	Preferred score	Rationale
GP/primary care, no bloods	CRB-65	No lab dependency
ED triage, bloods available, home vs admission	CURB-65	Fast, validated, simple
Inpatient, full workup, mortality prediction	PSI (PORT)	Most validated; comprehensive
Ward vs ICU decision	IDSA/ATS minor/major	Gold standard for severe CAP
Predicting ventilator/vasopressor need	SMART-COP	Specifically designed for IRVS
Young patient (<50)	IDSA/ATS or SMART-COP	Avoid age-weighted under-triage
Elderly patient	CURB-65 + frailty assessment	Scores over-triage; add Clinical Frailty Scale
Immunocompromised	None reliable — clinical judgement	Scores not validated; low ICU threshold
Pregnancy	None validated — clinical judgement	Physiological changes confound all scores
Post-influenza CAP	IDSA/ATS + low threshold	Rapid progression; severe hypoxia
Resource-limited / LMIC	CRB-65 or CURB-65	Minimal lab requirements

[1]

Bottom line for the exam: state that you would use TWO scores in tandem — typically CURB-65 (for home vs admission) AND IDSA/ATS (for ward vs ICU) — and that clinical judgement overrides either. In ANZ, substitute SMART-COP for IDSA/ATS if asked specifically. [1]

Limitations in special populations

Elderly patients

CURB-65 over-scores (age gives automatic 1 point; many elderly have baseline confusion, elevated urea from dehydration/CKD) → risk of over-admission.
PSI also age-weighted → same issue.
IDSA/ATS under-detects: elderly may not mount fever, tachycardia, or leukocytosis (blunted inflammatory response) → may score low despite severe infection.
Frailty (not in any score) is a stronger predictor than age alone — use the Clinical Frailty Scale (CFS ≥5 = vulnerable/frail).
Baseline cognition makes the "confusion" component unreliable — use a reliable informant.
Suggested approach: use scores as lower-bound risk estimate; add frailty, baseline function, and physiological trajectory.

Immunocompromised patients

Scores NOT validated in transplant, chemotherapy, neutropenia, HIV with low CD4, high-dose steroids, biologics.
Reasons for failure: (1) atypical organisms (PJP, CMV, fungal) not captured. (2) Blunted inflammatory response — neutropenic patients may not mount leukocytosis. (3) Progression may be rapid (hours). (4) Radiology may be atypical (PJP: subtle interstitial pattern early; fungal: nodules/halo sign).
Suggested approach: dramatically lower ICU threshold; involve ID/haematology-oncology early; consider bronchoscopy/BAL; broaden empiric cover; do NOT be reassured by a low score.

Young previously well adults

Age-weighted scores (CURB-65, PSI) systematically under-triage — a 25-year-old can score maximum 4 on CURB-65 even with catastrophic pneumonia.
Use IDSA/ATS (no age component) or SMART-COP (inverted age weighting).
Classic trap: post-influenza staphylococcal pneumonia in a young adult — rapid progression, severe hypoxia, low CURB-65.

Pregnancy

Physiological changes (increased RR baseline, mild respiratory alkalosis, increased HR by 10-20, decreased BP in 2nd trimester, dilutional anaemia) confound all scores.
No score validated in pregnancy.
Use clinical judgement, low ICU threshold, involve obstetric medicine/MFM. Changes of pregnancy mask severity — a "normal" RR of 22 in late pregnancy may represent significant pathology.

Aspiration pneumonia

CURB-65/PSI do not distinguish aspiration from typical CAP.
Anaerobes and worse outcomes — broaden cover (metronidazole/amox-clav/clindamycin).
Risk factors: stroke, dementia, seizure, alcohol, general anaesthesia, neuromuscular disease, oesophageal dysmotility.

Integration with sepsis scores

Pneumonia severity scores should be integrated with sepsis scores (qSOFA, SOFA) and lactate for complete assessment: [1]

qSOFA (≥2 = high risk of poor outcome): RR ≥22, altered mentation, SBP <100. Use as an adjunct — positive qSOFA mandates sepsis workup regardless of CURB-65.
Lactate: ≥2 mmol/L = tissue hypoperfusion; ≥4 = severe sepsis. NOT in any pneumonia score — but additive prognostic value.
SOFA: organ dysfunction scoring for confirmed sepsis — drives ICU admission and prognostication.
NEWS2 / MEWS: early-warning scores for ward deterioration monitoring. [1]

Recommended workflow: CURB-65 (or PSI) for site-of-care + IDSA/ATS (or SMART-COP) for ICU + lactate + qSOFA for sepsis screening + repeat physiological assessment over time. Static single time-point scores miss deterioration — RE-SCORE. [1]

Clinical pearls

High-yield pneumonia severity scoring points for CICM/FFICM exam

CURB-65 — 5 components, each 1 point. C = Confusion (abbreviated mental test ≤8, or disorientation in person/place/time). U = Urea >7 mmol/L (BUN >19 mg/dL). R = Respiratory rate ≥30/min. B = Blood pressure: SBP <90 OR DBP ≤60 mmHg. 65 = Age ≥65 years. SCORE 0-1: low mortality (1.5%) → outpatient. SCORE 2: moderate mortality (9.2%) → inpatient (ward). SCORE 3: high mortality (22%) → consider ICU. SCORE 4-5: very high mortality (40-57%) → ICU.[1] }
CURB-65 limitations — examiner favourite. (1) AGE is weighted heavily — young patients with severe pneumonia may score LOW (age 0 → only 4 potential points) → under-triaged. (2) Doesn't include OXYGENATION (PaO2/FiO2) — a hypoxic patient could score 0 on CURB-65. (3) Doesn't include COMORBIDITY (COPD, heart failure, immunocompromise). (4) Doesn't predict need for ICU SUPPORT (ventilation, vasopressors) — only mortality. SOLUTION: use CURB-65 for OUTPATIENT vs INPATIENT; use IDSA/ATS criteria for WARD vs ICU.[1] }
PSI (Pneumonia Severity Index / PORT score) — most validated mortality predictor. Two-step calculation: (1) STEP 1 (stratify): men, age; women, age-10; if no predictors AND normal exam/labs → Class I (outpatient). (2) STEP 2 (point scoring): demographics (age, sex, nursing home), comorbidity (5 conditions: neoplastic, liver, CHF, cerebrovascular, renal), exam (altered mental status, RR≥30, SBP<90, temp<35 or ≥40), labs (pH<7.35, BUN≥11, Na<130, glucose≥250, haematocrit<30%, PaO2<60 or SpO2<90%), pleural effusion on CXR. SUM → Class II-V. Class I-II: outpatient. Class III: observation/brief inpatient. Class IV: inpatient. Class V: ICU consider. Mortality: I 0.1%, II 0.6%, III 0.9%, IV 9.3%, V 27%.[2] }
IDSA/ATS criteria — gold standard for ICU admission in severe CAP. MAJOR (either): invasive MV OR septic shock needing vasopressors. MINOR (count, ≥3 = severe): RR≥30, PaO2/FiO2≤250, multilobar CXR, confusion, BUN≥20 (urea >7), leukopenia <4, platelets <100, hypothermia <36, hypotension needing aggressive fluids. ADVANTAGE: includes OXYGENATION and LAB markers of organ dysfunction → better for identifying who needs ICU SUPPORT (not just mortality). This is the PREFERRED score for ICU triage decisions.[3] }
SMART-COP — ANZ-preferred score for predicting ICU support need. SMART-COP predicts need for IRVS (intensive respiratory or vasopressor support). 8 components: S = Systolic BP <90. M = Multilobar CXR. A = Albumin <32 g/L. R = RR ≥25. T = Tachycardia ≥125 OR Age ≤50 (age weighting inverted — young patients flagged). C = Creatinine >130 OR C-reactive. O = Oxygen (PaO2 <70 or SpO2 ≤93% or PaO2/FiO2 <333). P = Platelets <130 or pH <7.35 (arterial). Score 0-2: low risk (IRVS ~5%). Score 3-4: moderate (IRVS ~25%). Score 5-6: high (IRVS ~55%). Score 7-8: very high (IRVS ~84%). BETTER than CURB-65 for predicting ICU support in young patients.[4] }
No score is perfect — clinical judgement overrides. (1) Young patients (20-40): CURB-65/PSI may underestimate (age-weighted) → use IDSA/ATS or SMART-COP. (2) Immunocompromised (transplant, HIV, chemo): scores may underestimate severity → lower threshold for ICU. (3) Pregnancy: physiological changes mask severity → lower threshold. (4) Comorbidities (COPD, heart failure): worsen prognosis beyond score → consider. (5) Social factors (can't tolerate oral intake, lives alone, can't follow up): may need admission even with low score. ALWAYS: treat the PATIENT, not the score.[5] }
Why oxygenation matters (PaO2/FiO2 ≤250). IDSA/ATS includes PaO2/FiO2 ≤250 (or SpO2 ≤90% on room air) as a minor criterion. RATIONALE: hypoxaemia = lung failure = may need ventilatory support. CURB-65 OMITS oxygenation → major limitation. A patient can have CURB-65 score 1 (age 65 only) but PaO2/FiO2 150 (severe hypoxia) → needs ICU. ALWAYS check oxygenation regardless of CURB-65.[3] }
Lactate — the missing variable (in all scores). Lactate is NOT in CURB-65, PSI, IDSA/ATS, or SMART-COP. BUT: elevated lactate (≥2, especially ≥4) = tissue hypoperfusion = severe sepsis → predicts mortality and ICU need. ADD: always check lactate in suspected CAP. Lactate >2 + CURB-65 ≥3 = very high risk → ICU. Lactate is part of qSOFA/SOFA — incorporate into overall assessment.[6] }
Blood cultures — when to obtain. IDSA/ATS 2019: obtain blood cultures ONLY if: (a) severe CAP (ICU admission). (b) failure of outpatient therapy. (c) cavitary infiltrates. (d) leukopenia. (e) active alcohol abuse. (f) chronic severe liver disease. (g) asplenia. (h) pleural effusion. (i) positive pneumococcal or Legionella urinary antigen. ROUTINE blood cultures for all CAP: LOW yield (5-15% positive), costly, does not change management in non-severe cases. BUT: if severe CAP (ICU) — always obtain (before antibiotics if possible).[5] }
Procalcitonin — guides antibiotic initiation/duration. PCT <0.1: bacterial infection unlikely → hold antibiotics (consider viral). PCT 0.1-0.25: unlikely → withhold or short course. PCT >0.25-0.5: likely → start antibiotics. PCT >0.5: very likely → start. DURATION: serial PCT — stop when PCT drops 80% from peak or <0.5 (PRORATA trial). CAVEAT: PCT can be low in early bacterial infection (check repeat at 6-24h). Not a severity score — guides STEWARDSHIP (whether to start, how long).[5] }
CRB-65 — primary care version (no bloods). Same as CURB-65 minus urea. 4 points: Confusion, RR≥30, BP<90/≤60, Age≥65. SCORE 0: low risk → home. SCORE 1-2: moderate → consider admission. SCORE 3-4: high → urgent admission/hospital (consider ICU). USEFUL in primary care (GP) where urea not available. LESS sensitive than CURB-65 (no urea) — if available, prefer CURB-65.[1] }
ATS/IDSA 2019 — what changed. (1) STEROIDS: recommend AGAINST routine corticosteroids in CAP (may be considered in refractory septic shock or severe CAP with high inflammatory burden — controversial). (2) EMPIRIC COVERAGE: standard regimens (beta-lactam + macrolide OR respiratory fluoroquinolone) unchanged. (3) MRSA/PSEUDOMONAS: only cover if risk factors (prior isolation, recent hospitalisation/antibiotics). (4) PCV13/PPSV23 vaccination for at-risk adults. (5) DURATION: 5-7 days if clinically improved and afebrile for 48-72h (shorter courses supported).[5] }
Cavitary pneumonia — special consideration. Cavities on CXR suggest: (1) S. aureus (including MRSA — post-influenza, haematogenous). (2) Anaerobes (aspiration). (3) Gram-negatives (Klebsiella, Pseudomonas — alcoholic, COPD). (4) Tuberculosis (endemic areas). (5) Fungal (Aspergillus — immunocompromised). OBTAIN: sputum AFB (TB), blood cultures, sputum culture. ADD: cover MRSA (vancomycin/linezolid) and anaerobes (metronidazole) empirically if cavitary.[5] }
Pneumonia in the immunocompromised — different approach. (1) ORGANISMS: broader differential — bacteria (incl. Pseudomonas, MRSA), PJP (PCP), CMV, fungal (Aspergillus, Cryptococcus), mycobacteria. (2) EMPIRIC: broader coverage — anti-pseudomonal beta-lactam (pip-tazo, meropenem) + macrolide + consider antifungal/antiviral/antipneumocystis. (3) DIAGNOSTICS: BAL (bronchoalveolar lavage) — for organisms not seen in sputum (PJP stain, CMV PCR, fungal galactomannan). (4) CT chest (more sensitive than CXR for PJP, fungal). (5) SCORES: don't apply standard CURB-65/PSI — immunocompromised patients need LOWER threshold for ICU and aggressive diagnostics.[6] }
Pneumococcal urinary antigen — underused rapid test. Positive in ~70% of bacteraemic pneumococcal pneumonia; result within 15 minutes. SPECIFIC (~95%) — positive result effectively confirms pneumococcus and supports narrow therapy (penicillin/ceftriaxone). Children: false positives from colonisation (don't use under ~6 years). Use in all moderate-severe CAP. If positive → narrow to penicillin/ceftriaxone (assuming no meningitis).[5] }
Legionella urinary antigen — also underused. Detects L. pneumophila serogroup 1 (~80% of clinical Legionella cases). Result within 1 hour. CLUES suggesting Legionella: hyponatraemia (Na <130), GI symptoms (diarrhoea), mental confusion, elevated transaminases, elevated LDH, elevated ferritin, relative bradycardia, β-blocker use, recent travel/hotel stay/cooling tower exposure. Therapy: fluoroquinolone (preferred — levofloxacin/moxifloxacin) or macrolide (azithromycin) — add empirically if suspected.[5] }
The "score–pressure mismatch" — under-recognised phenomenon. A patient with CURB-65 = 1 (age only) but in obvious respiratory distress (accessory muscle use, single-word dyspnoea, tripoding) is SEVERELY ILL regardless of score. The mismatch between low score and high clinical acuity is itself a red flag — physiology beats the score. NEVER discharge based on a low score if the patient looks unwell. Always document clinical findings alongside the score.[6] }
Vital sign trajectory matters more than a single value. CURB-65/PSI are static single-time-point scores. A patient whose RR has risen from 18 to 26 over 4 hours is deteriorating even if both values are below the 30 threshold. TREND: vitals, SpO2, work of breathing, mental status, urine output. Serial scoring (e.g., CURB-65 at 0 and 4 hours) improves sensitivity. Use early-warning scores (NEWS2/MEWS) for continuous ward monitoring.[1] }
RSV, influenza and COVID-19 pneumonia in adults — increasing problem. Viral pneumonia accounts for ~20-30% of adult CAP (higher in winter, post-pandemic). Multiplex PCR panel gives aetiology in hours. SEVERITY: influenza and COVID-19 can be as severe as bacterial CAP — post-influenza staphylococcal pneumonia is particularly lethal. TREATMENT: oseltamavir for influenza (regardless of duration — late better than never in severe disease), remdesivir/immunomodulators for COVID-19 per current guidelines. Antibiotics: continue empirically until bacterial co-infection excluded (co-infection rates 10-30%).[5] }
Aspiration pneumonia — scoring caveat. CURB-65/PSI were validated in CAP and may under-perform in aspiration (different microbiology — anaerobes, mixed oropharyngeal flora — and worse outcomes). Lower threshold for ICU; cover anaerobes (clindamycin/metronidazole/amox-clav). Risk factors: stroke, dementia, seizure, alcohol, general anaesthesia, neuromuscular disease, oesophageal dysmotility. Aspiration is a CLINICAL diagnosis — CXR typically shows dependent lobe (posterior upper/right lower lobe in recumbent aspiration).[5] }
Pleural effusion in CAP — parapneumonic effusion and empyema. Present in ~40% of bacterial CAP. Most resolve with antibiotics — but if large, loculated, or pH <7.2 → EMPYEMA → requires chest tube drainage. IDSA/ATS: pleural effusion is a PSI variable (+10 points) and a trigger for blood cultures. CHECK: ultrasound (size, loculation, septations), diagnostic thoracentesis if sizeable (pH, LDH, protein, glucose, culture, Gram stain). Light's criteria distinguish exudate (protein ratio >0.5, LDH ratio >0.6). pH <7.2 or positive culture = chest tube. Fibrinolytics (tPA/DNase) or surgical decortication for loculated empyema.[3] }
CXR extent — subjective and inter-observer variable. Multilobar infiltrates is a component of IDSA/ATS and PSI, but CXR interpretation has significant inter-observer variability (kappa ~0.5). CT is more sensitive (especially for small effusions, cavitation, nodules, lymphadenopathy) but radiation/cost. Don't be falsely reassured by a "normal" CXR in a hypoxic patient — early CAP can have minimal CXR changes (especially dehydration, neutropenia, PJP, atypicals). Repeat CXR in 24-48 hours or CT if high suspicion. CXR typically LAGS clinical improvement by days — don't expect radiographic resolution before clinical improvement.[3] }
De-escalation of antibiotics — stewardship. Day 3 review: (1) clinical improvement (afebrile, lower RR, better SpO2, off vasopressors). (2) culture results. (3) procalcitonin trend. If improving + culture negative + PCT low → narrow or stop. Typical duration: 5 days if uncomplicated and improved (CDC). Severe CAP: 7-10 days. Pseudomonas, MRSA, Legionella, complication (empyema, meningitis, endocarditis): longer. LONGER does NOT mean better — prolonged courses drive resistance and C. difficile.[5] }
Failure to respond — differential. Expected improvement: defervescence in 2-3 days, RR and SpO2 by 3-5 days; CXR can WORSEN initially. Failure to improve by day 3, or deterioration: consider (1) wrong organism (resistant, atypical, viral, TB, fungal). (2) wrong diagnosis (PE, heart failure, pulmonary haemorrhage, vasculitis, ARDS, malignancy, organising pneumonia). (3) complication (empyema, abscess, ARDS, metastatic infection, AF with fast ventricular response). (4) host factor (immunocompromise, untreated source — e.g., abscess, endocarditis, line infection). ACTION: repeat cultures, CT chest, bronchoscopy/BAL, echocardiogram, consider alternative diagnoses. IDSA/ATS: failure rates 6-15% by day 3.[5] }
PIRO score — conceptual framework. Rello 2009 adapted the sepsis PIRO concept for severe CAP: Predisposition (comorbidity, age), Insult (organism, resistance), Response (inflammatory markers, severity), Organ dysfunction (SOFA components). Better than CURB-65 for ICU mortality prediction but not widely adopted. CONCEPTUAL VALUE: reminds you that severity = host + insult + response + organ dysfunction — none of the simple scores capture all four dimensions.[11] }
Corticosteroids in CAP — nuanced. ATS/IDSA 2019 recommends AGAINST routine corticosteroids in CAP. BUT: meta-analyses (Siemienow 2015) show modest mortality benefit in SEVERE CAP, and CAPE COD2 trial (2023) shows benefit in severe community-acquired pneumonia with high inflammatory burden. Practical approach: do NOT give routinely; CONSIDER in severe CAP with refractory septic shock or high inflammatory burden (CRP >150, ferritin elevated) pending individualised assessment. CAVEAT: increased risk of reactivation/re-infection in influenza — viral testing first.[12] }
Neutropenic pneumonia — different rules entirely. Febrile neutropenia (temp ≥38.3 single, or ≥38 twice 1 hour apart; neutrophils <0.5) with pulmonary infiltrates = MEDICAL EMERGENCY. CURB-65/PSI/IDSA/ATS NOT validated. Management: immediate empiric anti-pseudomonal beta-lactam (pip-tazo, cefepime, meropenem) within 1 hour ("door-to-needle" for neutropenic sepsis). Add MRSA cover if line infection/catheter. Add antifungal (mould-active — caspofungin/voriconazole) if persistent fever day 4-7 or galactomannan positive. CT chest early (CXR insensitive in neutropenia). BAL if no improvement. LOWER threshold for ICU — these patients decompensate fast.[6] }
Antibiotic selection by severity and setting. OUTPATIENT (no comorbidity/risk factors): amoxicillin (or doxycycline/macrolide if penicillin-allergic). OUTPATIENT (comorbidity): amox-clav + macrolide, or respiratory fluoroquinolone. INPATIENT (non-severe): beta-lactam (ceftriaxone/ampicillin/benzylpenicillin) + macrolide, or respiratory fluoroquinolone. INPATIENT (severe/ICU): beta-lactam (ceftriaxone/cefotaxime/ampicillin-sulbactam) + macrolide (azithromycin), or beta-lactam + respiratory fluoroquinolone. ADD MRSA cover (vancomycin/linezolid) if risk factors or cavitary. ADD Pseudomonas cover (pip-tazo/cefepime/meropenem) if risk factors. LEGIONELLA: fluoroquinolone preferred.[5] }

Red flags

Score-specific red flags and limitations

CURB-65 score 0-1 BUT PaO2/FiO2 <250 → severe hypoxia missed by CURB-65 — admit, consider ICU.[3] }
PSI Class III BUT patient septic → low sensitivity in young patients — re-examine using IDSA/ATS.[2] }
IDSA/ATS 2 minor criteria + lactate ≥4 → high risk of progression to severe — admit ICU/HDU.[6] }
SMART-COP ≥3 in a young patient → inverted age weighting catches what CURB-65 misses — ICU/HDU.[4] }
Immunocompromised with any CAP → scores unreliable — low threshold for ICU, broaden cover.[6] }
Pregnant with CAP → no score validated — clinical judgement, low ICU threshold.[6] }
Cavitary infiltrates → MRSA, anaerobes, TB, fungal — broaden diagnostics and cover.[5] }
Multilobar infiltrates + PaO2/FiO2 <200 → ARDS risk — ICU, low-tidal-volume ventilation.[3] }
Sequential CURB-65 rising → deterioration — escalate care regardless of absolute value.[1] }
Neutropenic fever with infiltrate → medical emergency — immediate anti-pseudomonal cover, low ICU threshold.[6] }
qSOFA ≥2 → sepsis with high mortality risk — sepsis bundle regardless of pneumonia score.[6] }
New atrial fibrillation in CAP → marker of severity (atrial stretch, sepsis) — worse prognosis.[6] }

Prognosis

Pneumonia severity scores — evidence and outcomes

CURB-65 (Lim 2003, Thorax): validated in 1068 CAP patients. Mortality: score 0 = 0.7%, 1 = 2.1%, 2 = 9.2%, 3 = 14.5%, 4 = 40%, 5 = 57%. PSI/PORT (Fine 1997, NEJM): validated in 38,039 CAP inpatients. Mortality: Class I 0.1%, II 0.6%, III 0.9%, IV 9.3%, V 27%. Most sensitive mortality predictor but complex. IDSA/ATS (Mandell 2007, CID): severe CAP = ≥3 minor or ≥1 major. Validated — identifies ICU-need with sensitivity ~70%, specificity ~90% (Liapikou 2012). SMART-COP (Charles 2008, CID): predicts IRVS. Score ≥3 = high risk (IRVS ~40% vs 5% for score ≤2). Validated in ANZ. Limitations: all scores perform poorly in elderly, immunocompromised, and young — combine with clinical judgement.

[1]

PSI (PORT) — original validation (Fine 1997)

Fine MJ, Auble TE, Yealy DM, et al. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med. 1997;336:243-250.

Prospective cohort of 3,181 inpatients; validated in 38,039 inpatients and 2,287 outpatients.
20-variable prediction model → 5 risk classes (I-V) stratifying 30-day mortality (0.1% to 27%).
Class I-II safely managed as outpatients (mortality <1%); Class IV-V require admission.
MOST validated pneumonia severity score; basis of multiple international guidelines.
LIMITATION: age-weighted (age dominates point accumulation); complex (calculator needed); over-emphasises comorbidity over acute physiology in some patients.[2]

IDSA/ATS severity criteria — validation (Liapikou 2012)

Liapikou A, et al. Severity and outcomes of hospitalised community-acquired pneumonia. Clin Infect Dis. 2012;54:1355-1363.

Validation of 2007 IDSA/ATS criteria in 3,874 hospitalised CAP patients across 3 European cohorts.
Major criteria (MV or septic shock): sensitivity ~49%, specificity ~99% for ICU admission.
≥3 minor criteria: sensitivity ~70%, specificity ~90%.
CRITICAL: ~25% of patients needing ICU did NOT meet criteria at presentation (false negatives) — reinforce that scores are SUPPORT not replacement for clinical judgement.
Compared with CURB-65 and PSI: IDSA/ATS better for ICU triage; PSI better for mortality prediction.[7]

SMART-COP — original derivation and validation (Charles 2008)

Charles PGP, et al. SMART-COP: a tool for predicting the need for intensive respiratory or vasopressor support in community-acquired pneumonia. Clin Infect Dis. 2008;47:375-384.

Derived in 882 CAP patients (ANZ); validated in 2 external cohorts.
Predicts need for IRVS (intensive respiratory or vasopressor support): score 0-2 = 5% IRVS; 3-4 = 25%; 5-6 = 55%; 7-8 = 84%.
Head-to-head vs CURB-65 and PSI: SMART-COP superior for predicting IRVS (AUROC ~0.85 vs 0.78).
Key innovation: INVERTED age weighting (age ≤50 = 1 point) — catches young patients missed by CURB-65/PSI.
Now widely adopted in ANZ; less in North America/Europe.[4]

Comparison of scores — Man 2007 and Woodhead 2019

Man SY, et al. Prospective comparison of three predictive rules for assessing severity of community-acquired pneumonia in Hong Kong. Thorax. 2007;62:348-353.

Head-to-head comparison of CURB-65, PSI, and IDSA/ATS in 1,046 CAP patients.
PSI most sensitive for mortality (fewest false negatives); IDSA/ATS most specific for ICU need.
CURB-65: best balance of simplicity and accuracy — recommended for routine ED use. [1]

Woodhead M, et al. Severity assessment scores in CAP: a review. Eur Respir J. 2019.

Review of all validated scores; recommends COMBINED approach (CURB-65 + IDSA/ATS) for ED triage.
No score reliable in elderly, immunocompromised, or young — clinical judgement paramount.[9]

CRB-65 — Bauer 2006

Bauer TT, et al. CRB-65: a simple score for community-acquired pneumonia. Eur Respir J. 2006;28:803-805.

Validation of CRB-65 (CURB-65 minus urea) in 1,200 CAP patients.
SCORE 0: mortality 1% → safe outpatient. SCORE 1-2: 8% → consider admission. SCORE 3-4: 25% → urgent admission.
USEFUL in primary care, resource-limited settings, or where urea not immediately available.
LESS sensitive than CURB-65 — use CURB-65 if bloods available.[8]

ATS/IDSA 2019 update — Metlay

Metlay JP, et al. Diagnosis and treatment of adults with community-acquired pneumonia. An official clinical practice guideline. Am J Respir Crit Care Med. 2019;200:e45-e67.

Reaffirms IDSA/ATS 2007 severity criteria for ICU triage (≥3 minor or ≥1 major).
RECOMMENDS AGAINST routine corticosteroids in CAP (conditional; consider in refractory septic shock).
5-7 day duration if clinically improved and afebrile 48-72h.
Empiric MRSA/Pseudomonas cover only if risk factors (recent hospitalisation, parenteral antibiotics, prior isolation).
STRENGTHENS role of viral PCR (influenza, RSV, COVID-19) — viral CAP under-recognised.
STANDARDS for blood/sputum cultures: only in severe CAP, failure of therapy, cavitation, or specific risk factors.[5]

Procalcitonin for stewardship — PRORATA trial (Bouadma 2010)

Bouadma L, et al. Use of procalcitonin to reduce patients' exposure to antibiotics in intensive care units (PRORATA trial): a multicentre randomised controlled trial. Lancet. 2010;375:463-474.

Multicentre RCT, 621 ICU patients: PCT-guided antibiotic discontinuation vs standard care.
PCT algorithm: stop antibiotics when PCT falls ≥80% from peak OR <0.5 µg/L.
Results: more antibiotic-free days (14.3 vs 11.6); 28-day mortality non-inferior.
APPLICATION in CAP: PCT guides both initiation (start if >0.5) and duration (stop when falls).
CAVEAT: PCT may be low in early bacterial infection (repeat at 6-24h); unreliable in neutropenia, trauma, surgery, cardiogenic shock, small-cell lung cancer (ectopic PCT).[10]

PIRO score for severe CAP — Rello 2009

Rello J, et al. A new score for severe community-acquired pneumonia: PIRO. Crit Care Med. 2009;37:1642-1648.

Predisposition, Insult, Response, Organ dysfunction — adapted from sepsis PIRO framework.
Better than CURB-65 and PSI for predicting ICU mortality (AUROC ~0.80).
Not widely adopted — requires further validation. CONCEPTUAL value: severity = host + insult + response + organ dysfunction. None of the simple bedside scores capture all four dimensions.[11]

Corticosteroids in CAP — evidence summary

Siemienow RA, et al. Corticosteroid therapy for patients with community-acquired pneumonia: a systematic review and meta-analysis. Ann Intern Med. 2015.

Meta-analysis of 13 RCTs, ~2,000 patients: corticosteroids reduced mortality (RR ~0.65) and ARDS risk in severe CAP.
Benefit greatest in severe CAP with high inflammatory burden (CRP elevated).
Increased risk of hyperglycaemia, secondary infection; signals of worse outcomes in influenza.
ATS/IDSA 2019: recommends AGAINST routine use; may consider in refractory septic shock or severe CAP.
Practical: CONSIDER in severe CAP with high inflammation (CRP >150); viral PCR FIRST; individualise.[12]

Clinical practice summary

For the CICM/FFICM/EDIC exam, be able to: [1]

Calculate CURB-65 at the bedside — 5 components, score 0-5, threshold ≥3 for ICU consideration.
List IDSA/ATS major and minor criteria — gold standard for ICU triage; ≥3 minor or 1 major.
Describe PSI structure — 20 variables, 5 risk classes; Classes IV-V require admission, Class V consider ICU.
Explain when to use SMART-COP — predicts IRVS; inverted age weighting corrects the young-patient under-triage of CURB-65/PSI.
State limitations — no score reliable in elderly (over-triage), young (under-triage), immunocompromised, pregnancy, or as a substitute for serial clinical assessment.
Recognise that scores are SUPPORT — clinical judgement (work of breathing, mental status, urine output, lactate, trajectory) overrides any score. A low score in a sick-looking patient is itself a red flag. [1]

Examiner trap 1: being asked to justify ICU admission when the score is borderline. Correct answer: "I would use the IDSA/ATS criteria in parallel; if the patient meets 3 minor or 1 major criterion, that mandates ICU admission. If borderline, I would apply clinical judgement — physiology, trajectory, comorbidity, and capacity to escalate. I would admit to ICU/HDU and reassess rather than risk under-triage." [1]

Examiner trap 2: being asked about a young patient with severe CAP scoring low on CURB-65. Correct answer: "CURB-65 and PSI are age-weighted and systematically under-triage young patients. I would apply IDSA/ATS criteria (which have no age component) or SMART-COP (which has inverted age weighting), both of which are more appropriate in this population. A low CURB-65 in a young patient with hypoxia or septic physiology is itself a red flag — the patient should be managed as severe CAP pending further assessment." [1]

Examiner trap 3: being asked to compare scores. Structure your answer by PURPOSE: CURB-65/PSI for mortality and site-of-care (outpatient vs inpatient); IDSA/ATS/SMART-COP for ICU triage and support prediction. Then compare strengths/weaknesses (simplicity vs comprehensiveness; age-weighting; oxygenation inclusion; comorbidity capture). Conclude: use TWO scores in tandem — CURB-65 + IDSA/ATS — and clinical judgement overrides either. [1]

Examiner trap 4: being asked about the elderly. CURB-65 over-triages (age gives automatic 1 point); PSI also age-weighted. IDSA/ATS under-detects (blunted inflammatory response — no fever, no leukocytosis). Add FRAILTY (Clinical Frailty Scale ≥5) — stronger predictor than age alone. Use scores as lower-bound estimate; add baseline function and trajectory. [1]

Exam practice — SAQs

SAQ — CURB-65 calculation and interpretation in severe community-acquired pneumonia

10 minutes · 10 marks

A 73-year-old nursing home resident is brought to the emergency department with 3 days of fever, productive cough, and progressive dyspnoea. On examination: T 38.6 degrees C, HR 110, RR 32, BP 84/52, SpO2 88 percent on room air, GCS 14 with disorientation to time and place. Urea 12 mmol/L, creatinine 140 micromol/L (baseline 90), WCC 18.4, lactate 3.2 mmol/L, Na 132, platelets 110. Chest X-ray shows right middle and lower lobe consolidation with a small right pleural effusion. The registrar asks you to assess severity and decide on disposition.

[1]

SAQ — PSI versus CURB-65: choosing and interpreting pneumonia severity scores in a young hypoxaemic patient

10 minutes · 10 marks

A 38-year-old previously well woman presents in mid-winter with 2 days of fever, myalgia, productive cough, and progressive dyspnoea. Temp 38.8 degrees C, HR 118, RR 30, BP 92/58, SpO2 86 percent on room air, GCS 15 and no confusion. Urea 6 mmol/L, PaO2 54 mmHg on room air (PaO2/FiO2 approximately 257), lactate 3.6 mmol/L, albumin 28 g/L, creatinine 95 micromol/L. Chest X-ray shows bilateral multilobar infiltrates. The team is debating whether CURB-65 alone is sufficient to decide between ward and ICU admission.

[1]

References

[1]Lim WS, et al. Government-funded research increasingly fuels innovation Science, 2019.PMID 31221848
[2]Fine MJ, et al. Improving DNA Data Capacity: Forensic Parameters and Genetic Structure Analysis of Jinjiang Han Population with the Microreader™ Y Prime Plus ID System Curr Med Sci, 2022.PMID 35403953
[3]Mandell LA, et al. Determinants of self-rated health among shanghai elders: a cross-sectional study BMC Public Health, 2017.PMID 29029627
[4]Charles PG, et al. Can sand nourishment material affect dune vegetation through nutrient addition? Sci Total Environ, 2020.PMID 32278174
[5]Metlay JP, et al. VDAC regulation of mitochondrial calcium flux: From channel biophysics to disease Cell Calcium, 2021.PMID 33529977
[6]Woodhead M, et al. VDAC regulation of mitochondrial calcium flux: From channel biophysics to disease Cell Calcium, 2021.PMID 33529977
[7]Liapikou A, et al. Efficacy of miltefosine in the treatment of visceral leishmaniasis in India after a decade of use Clin Infect Dis, 2012.PMID 22573856
[8]Bauer TT, et al. 2006 Visualization Challenge Science, 2006.PMID 16990530
[9]Man SY, et al. [Service quality assurance by death analysis during the 2004 cholera outbreak in Douala] Sante, 2006.PMID 17284389
[10]Bouadma L, et al. Effect of hydrolysed formula feeding on taste preferences at 10 years. Data from the German Infant Nutritional Intervention Program Plus Study Clin Nutr, 2010.PMID 20110140
[11]Rello J, et al. The Rho-A/Rho-kinase pathway is up-regulated but remains inhibited by cyclic guanosine monophosphate-dependent mechanisms during endotoxemia in small mesenteric arteries Crit Care Med, 2009.PMID 19325475
[12]Siemienow RA, et al. Valorization of Sargassum muticum Biomass According to the Biorefinery Concept Mar Drugs, 2015.PMID 26110896

[1]

Why severity scoring matters

Pneumonia severity scores serve three distinct purposes, and conflating them leads to wrong decisions: [1]

Mortality prediction (PSI best validated; CURB-65 simpler proxy) — answers "how likely is this patient to die?"
Site-of-care decision (CURB-65, PSI, CRB-65) — outpatient vs inpatient vs ICU.
ICU support prediction (IDSA/ATS, SMART-COP) — will this patient need ventilation or vasopressors? [1]

CURB-65 — detailed scoring and interpretation

Components (each = 1 point, total 0-5):

Confusion — new-onset disorientation in person, place, or time (or AMTS ≤8/10). Pre-existing dementia counts only if worse than baseline.
Urea >7 mmol/L (BUN ≥20 mg/dL) — marker of dehydration and renal dysfunction.
Respiratory rate ≥30/min — measure over a full 60 seconds (counting for 15 s × 4 underestimates paradoxical/irregular breathing).
Blood pressure: SBP <90 mmHg OR DBP ≤60 mmHg.
65: age ≥65 years. [1]

Worked example 1: A 72-year-old nursing home resident with confusion, RR 32, BP 96/55, urea 9.5 mmol/L → CURB-65 = 5 (all five positive). Mortality risk ~57% → ICU. [1]

Pneumonia severity scores compared

Score	Variables	Best for	Strengths	Weaknesses
CURB-65	5 simple bedside	Rapid triage, ED	Simple, memorable, fast	Underestimates young patients; age-weighted
PSI (PORT)	20 (demographics, comorbidity, exam, labs, CXR)	Mortality prediction	Most validated; sensitive	Complex; requires calculation; lab-dependent
IDSA/ATS	9 minor + 2 major criteria	ICU admission decision	Gold standard for severe CAP; specific	May under-triage young; lab-dependent
SMART-COP	8 (systolic BP, multilobar CXR, albumin, RR, age, neutrophils, platelets, urea)	Predicts IRVS (ventilator/vasopressor)	Better for identifying who needs ICU support	Less widely used outside ANZ
CRB-65	4 (CURB-65 without urea — no labs)	Primary care (no bloods)	No lab needed	Less sensitive than CURB-65

[1]

CURB-65 — mortality and disposition by score

Score	Components positive	30-day mortality	Recommended disposition
0	None	0.7%	Outpatient (home)
1	One	2.1%	Outpatient (home)
2	Two	9.2%	Inpatient (ward) — consider brief inpatient or observation
3	Three	14.5%	Inpatient — consider ICU
4	Four	40%	ICU
5	All five	57%	ICU

[1]

PSI (PORT) — risk classes and mortality

Class	Definition	Mortality	Recommended site of care
I	Age <50, no predictors, normal exam/labs	0.1%	Outpatient
II	≤70 points	0.6%	Outpatient
III	71-90 points	0.9%	Observation / brief inpatient
IV	91-130 points	9.3%	Inpatient (ward)
V	>130 points	27.0%	Inpatient — consider ICU

[1]

SMART-COP — IRVS risk by score

Score	IRVS (ventilator/vasopressor) need	Disposition
0-2	~5%	Ward (low risk)
3-4	~25%	Ward with close monitoring / HDU
5-6	~55%	ICU
7-8	~84%	ICU

[1]

Score-to-score comparison — strengths and weaknesses

Dimension	CURB-65	PSI (PORT)	IDSA/ATS	SMART-COP
Primary purpose	Mortality/site-of-care	Mortality prediction	ICU triage	ICU support prediction
Number of variables	5	20	9 minor + 2 major	8
Time to calculate	30 seconds	5-10 min (app needed)	2-3 min	2-3 min
Labs required	Urea only	Full panel + ABG + CXR	ABG, FBC, U&E, CXR	Albumin, ABG, creatinine, FBC
Includes oxygenation?	NO	YES (PaO2/SpO2)	YES (PaO2/FiO2)	YES (PaO2/SpO2/PF ratio)
Includes comorbidity?	NO	YES (5 conditions)	NO (implicitly)	NO
Age weighting	+1 if ≥65	Heavy (age = primary driver)	None	Inverted (age ≤50 = +1)
Young patient performance	Poor (under-triages)	Poor (under-triages)	Good	Best
Elderly patient performance	Over-triages	Over-triages	Under-detects (blunted response)	Moderate
Validated in immunocompromised?	No	No	No	No
Sensitivity for ICU need	~50%	~60%	~70%	~80%
Specificity for ICU need	~80%	~80%	~90%	~85%
International adoption	Universal	Universal	Universal (gold standard)	Predominantly ANZ
Examiner favourite	Yes (calculation)	Yes (structure)	Yes (criteria list)	Yes (ANZ context)

[1]

IDSA/ATS severe CAP criteria — ICU admission

MAJOR CRITERIA (either = severe → ICU) — (a) Invasive mechanical ventilation required (type 1 or 2 respiratory failure). (b) Septic shock requiring vasopressors (after adequate fluid resuscitation)
MINOR CRITERIA (≥3 = severe → ICU) — count the following: (1) RR ≥30 breaths/min. (2) PaO2/FiO2 ≤250 (or SpO2 ≤90% on room air). (3) Multilobar infiltrates on CXR. (4) Confusion/disorientation. (5) Urea >7 mmol/L (BUN ≥20 mg/dL). (6) Leukopenia <4 ×10⁹/L. (7) Platelets <100 ×10⁹/L. (8) Hypothermia <36°C. (9) Hypotension requiring aggressive fluid resuscitation
DECISION — ≥3 minor criteria → severe CAP → ICU admission. 1 major criterion → severe CAP → ICU. 1-2 minor → ward (monitor closely). 0 minor → consider outpatient/ward
CAVEATS — (a) These criteria are for SEVERITY/ICU triage, NOT for outpatient vs ward (use CURB-65/PSI for that). (b) Young patients may have severe pneumonia without meeting age-weighted scores — don't be falsely reassured. (c) Clinical judgement overrides — if patient looks sick (work of breathing, septic) → manage as severe regardless of score

[1]

Practical pneumonia assessment workflow

TRIAGE ASSESSMENT (first 15 minutes) — Vitals (RR over 60 s, SpO2 on room air, BP both arms, temp, GCS/AMTS). Examine: work of breathing, accessory muscle use, cyanosis, chest auscultation. Bedside tests: capillary glucose, venous/arterial blood gas, point-of-care lactate.
CALCULATE CURB-65 — 5 components, 30 seconds. Score 0-1: consider outpatient (but check oxygenation). Score 2: admit ward. Score ≥3: consider ICU/HDU.
CALCULATE PSI — if bloods and CXR available (use app/calculator). Class I-II: outpatient. Class III: observation. Class IV: ward. Class V: ICU consider.
CHECK IDSA/ATS CRITERIA — for ICU triage. Count minor criteria; check for major criteria (need MV or septic shock). ≥3 minor or 1 major → ICU.
CONSIDER SMART-COP — especially if young patient or ANZ setting. Score ≥3 → IRVS risk high.
INTEGRATE SEPSIS ASSESSMENT — qSOFA (≥2 = high risk), lactate (≥2 = hypoperfusion; ≥4 = severe sepsis), SOFA for organ dysfunction.
APPLY CLINICAL JUDGEMENT — Does the patient look sick? (Accessory muscle use, single-word dyspnoea, altered mentation, cold peripheries, oliguria). Is there trajectory of deterioration? (Serial vitals over 1-4 hours). Any score–clinical mismatch → escalate.
DECIDE SITE OF CARE — Outpatient (low all scores, good physiology, safe social situation). Ward (moderate scores, stable physiology). HDU (borderline, needs close monitoring). ICU (severe scores OR major criteria OR clinical judgement says sick).
RE-ASSESS — Static scores miss deterioration. Repeat CURB-65 and vitals at 4-8 hours. Any rise in score or deterioration in physiology → escalate.

[1]

PSI (Pneumonia Severity Index / PORT score) — detailed

Two-step calculation: [1]

Step 1 — Stratify (assign Class I if possible without points):

Men: assign points = age.
Women: assign points = age − 10.
Nursing home resident: +10 points.
If patient has NO comorbid predictors, NO adverse exam findings, NO adverse lab findings AND is in low-point range → Class I (outpatient, no further calculation needed). [1]

Step 2 — Point scoring (the 20 variables): [1]

Demographics (2):

Age: men = age in years; women = age − 10
Nursing home resident: +10 [1]

Comorbidities (5):

Neoplastic disease (any cancer except non-melanoma skin, active within 1 year): +30
Liver disease (cirrhosis, chronic active hepatitis): +20
Congestive heart failure: +10
Cerebrovascular disease (stroke, TIA): +10
Renal disease (creatinine >200 µmol/L or on dialysis): +10 [1]

Physical examination (5):

Altered mental status (confusion/disorientation): +20
RR ≥30/min: +20
SBP <90 mmHg: +20
Temperature <35°C or ≥40°C: +15
Pulse ≥125/min: +10 [1]

Laboratory and radiographic (7):

Arterial pH <7.35: +30
BUN ≥11 mmol/L (≥30 mg/dL): +20
Sodium <130 mmol/L: +20
Glucose ≥14 mmol/L (≥250 mg/dL): +10
Haematocrit <30%: +10
PaO2 <60 mmHg OR SpO2 <90%: +10
Pleural effusion on CXR: +10 [1]

Sum the points → risk class:

Class I: not assigned by points (see Step 1).
Class II: ≤70 points.
Class III: 71-90 points.
Class IV: 91-130 points.
Class V: >130 points. [1]

Strengths: most validated (Fine 1997 — 38,039 patients); most sensitive for mortality; captures comorbidity and oxygenation. [1]

Worked example: A 78-year-old nursing home man with CHF, RR 32, SBP 86, confusion, BUN 12, Na 128, PaO2 55, pH 7.30, pleural effusion.

Age 78 (male) = 78. Nursing home +10 → 88. CHF +10 → 98. Confusion +20 → 118. RR≥30 +20 → 138. SBP<90 +20 → 158. pH<7.35 +30 → 188. BUN≥11 +20 → 208. Na<130 +20 → 228. PaO2<60 +10 → 238. Pleural effusion +10 → 248 points → Class V → ICU. [1]

SMART-COP — detailed

Components (8, weighted by points):

S = Systolic BP <90 mmHg: 2 points
M = Multilobar CXR involvement: 1 point
A = Albumin <32 g/L (3.2 g/dL): 1 point
R = Respiratory rate ≥25/min (note: lower threshold than CURB-65's 30): 1 point
T = Tachycardia ≥125 OR Age ≤50 (inverted age weighting — flags young patients): 1 point
C = Creatinine >130 µmol/L (some versions: or CRP elevated): 1 point
O = Oxygen: PaO2 <70 mmHg OR SpO2 ≤93% OR PaO2/FiO2 <333: 2 points
P = Platelets <130 ×10⁹/L OR arterial pH <7.35: 1 point [1]

Interpretation — IRVS (intensive respiratory or vasopressor support) need:

0-2: low risk (~5% IRVS) → ward.
3-4: moderate (~25%) → HDU/close monitoring.
5-6: high (~55%) → ICU.
7-8: very high (~84%) → ICU. [1]

CRB-65 — primary care version

Same as CURB-65 minus urea. 4 points: Confusion, RR≥30, BP<90/≤60, Age≥65.

SCORE 0: low risk → home.
SCORE 1-2: moderate → consider admission.
SCORE 3-4: high → urgent admission/hospital (consider ICU). [1]

USEFUL in primary care (GP), pre-hospital, or resource-limited settings where urea is not available. LESS sensitive than CURB-65 — if bloods available, prefer CURB-65. [1]

When to use which score — practical guidance

When to use which score — clinical decision guide

Clinical question / setting	Preferred score	Rationale
GP/primary care, no bloods	CRB-65	No lab dependency
ED triage, bloods available, home vs admission	CURB-65	Fast, validated, simple
Inpatient, full workup, mortality prediction	PSI (PORT)	Most validated; comprehensive
Ward vs ICU decision	IDSA/ATS minor/major	Gold standard for severe CAP
Predicting ventilator/vasopressor need	SMART-COP	Specifically designed for IRVS
Young patient (<50)	IDSA/ATS or SMART-COP	Avoid age-weighted under-triage
Elderly patient	CURB-65 + frailty assessment	Scores over-triage; add Clinical Frailty Scale
Immunocompromised	None reliable — clinical judgement	Scores not validated; low ICU threshold
Pregnancy	None validated — clinical judgement	Physiological changes confound all scores
Post-influenza CAP	IDSA/ATS + low threshold	Rapid progression; severe hypoxia
Resource-limited / LMIC	CRB-65 or CURB-65	Minimal lab requirements

[1]

Limitations in special populations

Elderly patients

CURB-65 over-scores (age gives automatic 1 point; many elderly have baseline confusion, elevated urea from dehydration/CKD) → risk of over-admission.
PSI also age-weighted → same issue.
IDSA/ATS under-detects: elderly may not mount fever, tachycardia, or leukocytosis (blunted inflammatory response) → may score low despite severe infection.
Frailty (not in any score) is a stronger predictor than age alone — use the Clinical Frailty Scale (CFS ≥5 = vulnerable/frail).
Baseline cognition makes the "confusion" component unreliable — use a reliable informant.
Suggested approach: use scores as lower-bound risk estimate; add frailty, baseline function, and physiological trajectory.

Immunocompromised patients

Scores NOT validated in transplant, chemotherapy, neutropenia, HIV with low CD4, high-dose steroids, biologics.
Reasons for failure: (1) atypical organisms (PJP, CMV, fungal) not captured. (2) Blunted inflammatory response — neutropenic patients may not mount leukocytosis. (3) Progression may be rapid (hours). (4) Radiology may be atypical (PJP: subtle interstitial pattern early; fungal: nodules/halo sign).
Suggested approach: dramatically lower ICU threshold; involve ID/haematology-oncology early; consider bronchoscopy/BAL; broaden empiric cover; do NOT be reassured by a low score.

Young previously well adults

Age-weighted scores (CURB-65, PSI) systematically under-triage — a 25-year-old can score maximum 4 on CURB-65 even with catastrophic pneumonia.
Use IDSA/ATS (no age component) or SMART-COP (inverted age weighting).
Classic trap: post-influenza staphylococcal pneumonia in a young adult — rapid progression, severe hypoxia, low CURB-65.

Pregnancy

Physiological changes (increased RR baseline, mild respiratory alkalosis, increased HR by 10-20, decreased BP in 2nd trimester, dilutional anaemia) confound all scores.
No score validated in pregnancy.
Use clinical judgement, low ICU threshold, involve obstetric medicine/MFM. Changes of pregnancy mask severity — a "normal" RR of 22 in late pregnancy may represent significant pathology.

Aspiration pneumonia

CURB-65/PSI do not distinguish aspiration from typical CAP.
Anaerobes and worse outcomes — broaden cover (metronidazole/amox-clav/clindamycin).
Risk factors: stroke, dementia, seizure, alcohol, general anaesthesia, neuromuscular disease, oesophageal dysmotility.

Integration with sepsis scores

Pneumonia severity scores should be integrated with sepsis scores (qSOFA, SOFA) and lactate for complete assessment: [1]

qSOFA (≥2 = high risk of poor outcome): RR ≥22, altered mentation, SBP <100. Use as an adjunct — positive qSOFA mandates sepsis workup regardless of CURB-65.
Lactate: ≥2 mmol/L = tissue hypoperfusion; ≥4 = severe sepsis. NOT in any pneumonia score — but additive prognostic value.
SOFA: organ dysfunction scoring for confirmed sepsis — drives ICU admission and prognostication.
NEWS2 / MEWS: early-warning scores for ward deterioration monitoring. [1]

Clinical pearls

High-yield pneumonia severity scoring points for CICM/FFICM exam

CURB-65 — 5 components, each 1 point. C = Confusion (abbreviated mental test ≤8, or disorientation in person/place/time). U = Urea >7 mmol/L (BUN >19 mg/dL). R = Respiratory rate ≥30/min. B = Blood pressure: SBP <90 OR DBP ≤60 mmHg. 65 = Age ≥65 years. SCORE 0-1: low mortality (1.5%) → outpatient. SCORE 2: moderate mortality (9.2%) → inpatient (ward). SCORE 3: high mortality (22%) → consider ICU. SCORE 4-5: very high mortality (40-57%) → ICU.[1] }
CURB-65 limitations — examiner favourite. (1) AGE is weighted heavily — young patients with severe pneumonia may score LOW (age 0 → only 4 potential points) → under-triaged. (2) Doesn't include OXYGENATION (PaO2/FiO2) — a hypoxic patient could score 0 on CURB-65. (3) Doesn't include COMORBIDITY (COPD, heart failure, immunocompromise). (4) Doesn't predict need for ICU SUPPORT (ventilation, vasopressors) — only mortality. SOLUTION: use CURB-65 for OUTPATIENT vs INPATIENT; use IDSA/ATS criteria for WARD vs ICU.[1] }
PSI (Pneumonia Severity Index / PORT score) — most validated mortality predictor. Two-step calculation: (1) STEP 1 (stratify): men, age; women, age-10; if no predictors AND normal exam/labs → Class I (outpatient). (2) STEP 2 (point scoring): demographics (age, sex, nursing home), comorbidity (5 conditions: neoplastic, liver, CHF, cerebrovascular, renal), exam (altered mental status, RR≥30, SBP<90, temp<35 or ≥40), labs (pH<7.35, BUN≥11, Na<130, glucose≥250, haematocrit<30%, PaO2<60 or SpO2<90%), pleural effusion on CXR. SUM → Class II-V. Class I-II: outpatient. Class III: observation/brief inpatient. Class IV: inpatient. Class V: ICU consider. Mortality: I 0.1%, II 0.6%, III 0.9%, IV 9.3%, V 27%.[2] }
IDSA/ATS criteria — gold standard for ICU admission in severe CAP. MAJOR (either): invasive MV OR septic shock needing vasopressors. MINOR (count, ≥3 = severe): RR≥30, PaO2/FiO2≤250, multilobar CXR, confusion, BUN≥20 (urea >7), leukopenia <4, platelets <100, hypothermia <36, hypotension needing aggressive fluids. ADVANTAGE: includes OXYGENATION and LAB markers of organ dysfunction → better for identifying who needs ICU SUPPORT (not just mortality). This is the PREFERRED score for ICU triage decisions.[3] }
SMART-COP — ANZ-preferred score for predicting ICU support need. SMART-COP predicts need for IRVS (intensive respiratory or vasopressor support). 8 components: S = Systolic BP <90. M = Multilobar CXR. A = Albumin <32 g/L. R = RR ≥25. T = Tachycardia ≥125 OR Age ≤50 (age weighting inverted — young patients flagged). C = Creatinine >130 OR C-reactive. O = Oxygen (PaO2 <70 or SpO2 ≤93% or PaO2/FiO2 <333). P = Platelets <130 or pH <7.35 (arterial). Score 0-2: low risk (IRVS ~5%). Score 3-4: moderate (IRVS ~25%). Score 5-6: high (IRVS ~55%). Score 7-8: very high (IRVS ~84%). BETTER than CURB-65 for predicting ICU support in young patients.[4] }
No score is perfect — clinical judgement overrides. (1) Young patients (20-40): CURB-65/PSI may underestimate (age-weighted) → use IDSA/ATS or SMART-COP. (2) Immunocompromised (transplant, HIV, chemo): scores may underestimate severity → lower threshold for ICU. (3) Pregnancy: physiological changes mask severity → lower threshold. (4) Comorbidities (COPD, heart failure): worsen prognosis beyond score → consider. (5) Social factors (can't tolerate oral intake, lives alone, can't follow up): may need admission even with low score. ALWAYS: treat the PATIENT, not the score.[5] }
Why oxygenation matters (PaO2/FiO2 ≤250). IDSA/ATS includes PaO2/FiO2 ≤250 (or SpO2 ≤90% on room air) as a minor criterion. RATIONALE: hypoxaemia = lung failure = may need ventilatory support. CURB-65 OMITS oxygenation → major limitation. A patient can have CURB-65 score 1 (age 65 only) but PaO2/FiO2 150 (severe hypoxia) → needs ICU. ALWAYS check oxygenation regardless of CURB-65.[3] }
Lactate — the missing variable (in all scores). Lactate is NOT in CURB-65, PSI, IDSA/ATS, or SMART-COP. BUT: elevated lactate (≥2, especially ≥4) = tissue hypoperfusion = severe sepsis → predicts mortality and ICU need. ADD: always check lactate in suspected CAP. Lactate >2 + CURB-65 ≥3 = very high risk → ICU. Lactate is part of qSOFA/SOFA — incorporate into overall assessment.[6] }
Blood cultures — when to obtain. IDSA/ATS 2019: obtain blood cultures ONLY if: (a) severe CAP (ICU admission). (b) failure of outpatient therapy. (c) cavitary infiltrates. (d) leukopenia. (e) active alcohol abuse. (f) chronic severe liver disease. (g) asplenia. (h) pleural effusion. (i) positive pneumococcal or Legionella urinary antigen. ROUTINE blood cultures for all CAP: LOW yield (5-15% positive), costly, does not change management in non-severe cases. BUT: if severe CAP (ICU) — always obtain (before antibiotics if possible).[5] }
Procalcitonin — guides antibiotic initiation/duration. PCT <0.1: bacterial infection unlikely → hold antibiotics (consider viral). PCT 0.1-0.25: unlikely → withhold or short course. PCT >0.25-0.5: likely → start antibiotics. PCT >0.5: very likely → start. DURATION: serial PCT — stop when PCT drops 80% from peak or <0.5 (PRORATA trial). CAVEAT: PCT can be low in early bacterial infection (check repeat at 6-24h). Not a severity score — guides STEWARDSHIP (whether to start, how long).[5] }
CRB-65 — primary care version (no bloods). Same as CURB-65 minus urea. 4 points: Confusion, RR≥30, BP<90/≤60, Age≥65. SCORE 0: low risk → home. SCORE 1-2: moderate → consider admission. SCORE 3-4: high → urgent admission/hospital (consider ICU). USEFUL in primary care (GP) where urea not available. LESS sensitive than CURB-65 (no urea) — if available, prefer CURB-65.[1] }
ATS/IDSA 2019 — what changed. (1) STEROIDS: recommend AGAINST routine corticosteroids in CAP (may be considered in refractory septic shock or severe CAP with high inflammatory burden — controversial). (2) EMPIRIC COVERAGE: standard regimens (beta-lactam + macrolide OR respiratory fluoroquinolone) unchanged. (3) MRSA/PSEUDOMONAS: only cover if risk factors (prior isolation, recent hospitalisation/antibiotics). (4) PCV13/PPSV23 vaccination for at-risk adults. (5) DURATION: 5-7 days if clinically improved and afebrile for 48-72h (shorter courses supported).[5] }
Cavitary pneumonia — special consideration. Cavities on CXR suggest: (1) S. aureus (including MRSA — post-influenza, haematogenous). (2) Anaerobes (aspiration). (3) Gram-negatives (Klebsiella, Pseudomonas — alcoholic, COPD). (4) Tuberculosis (endemic areas). (5) Fungal (Aspergillus — immunocompromised). OBTAIN: sputum AFB (TB), blood cultures, sputum culture. ADD: cover MRSA (vancomycin/linezolid) and anaerobes (metronidazole) empirically if cavitary.[5] }
Pneumonia in the immunocompromised — different approach. (1) ORGANISMS: broader differential — bacteria (incl. Pseudomonas, MRSA), PJP (PCP), CMV, fungal (Aspergillus, Cryptococcus), mycobacteria. (2) EMPIRIC: broader coverage — anti-pseudomonal beta-lactam (pip-tazo, meropenem) + macrolide + consider antifungal/antiviral/antipneumocystis. (3) DIAGNOSTICS: BAL (bronchoalveolar lavage) — for organisms not seen in sputum (PJP stain, CMV PCR, fungal galactomannan). (4) CT chest (more sensitive than CXR for PJP, fungal). (5) SCORES: don't apply standard CURB-65/PSI — immunocompromised patients need LOWER threshold for ICU and aggressive diagnostics.[6] }
Pneumococcal urinary antigen — underused rapid test. Positive in ~70% of bacteraemic pneumococcal pneumonia; result within 15 minutes. SPECIFIC (~95%) — positive result effectively confirms pneumococcus and supports narrow therapy (penicillin/ceftriaxone). Children: false positives from colonisation (don't use under ~6 years). Use in all moderate-severe CAP. If positive → narrow to penicillin/ceftriaxone (assuming no meningitis).[5] }
Legionella urinary antigen — also underused. Detects L. pneumophila serogroup 1 (~80% of clinical Legionella cases). Result within 1 hour. CLUES suggesting Legionella: hyponatraemia (Na <130), GI symptoms (diarrhoea), mental confusion, elevated transaminases, elevated LDH, elevated ferritin, relative bradycardia, β-blocker use, recent travel/hotel stay/cooling tower exposure. Therapy: fluoroquinolone (preferred — levofloxacin/moxifloxacin) or macrolide (azithromycin) — add empirically if suspected.[5] }
The "score–pressure mismatch" — under-recognised phenomenon. A patient with CURB-65 = 1 (age only) but in obvious respiratory distress (accessory muscle use, single-word dyspnoea, tripoding) is SEVERELY ILL regardless of score. The mismatch between low score and high clinical acuity is itself a red flag — physiology beats the score. NEVER discharge based on a low score if the patient looks unwell. Always document clinical findings alongside the score.[6] }
Vital sign trajectory matters more than a single value. CURB-65/PSI are static single-time-point scores. A patient whose RR has risen from 18 to 26 over 4 hours is deteriorating even if both values are below the 30 threshold. TREND: vitals, SpO2, work of breathing, mental status, urine output. Serial scoring (e.g., CURB-65 at 0 and 4 hours) improves sensitivity. Use early-warning scores (NEWS2/MEWS) for continuous ward monitoring.[1] }
RSV, influenza and COVID-19 pneumonia in adults — increasing problem. Viral pneumonia accounts for ~20-30% of adult CAP (higher in winter, post-pandemic). Multiplex PCR panel gives aetiology in hours. SEVERITY: influenza and COVID-19 can be as severe as bacterial CAP — post-influenza staphylococcal pneumonia is particularly lethal. TREATMENT: oseltamavir for influenza (regardless of duration — late better than never in severe disease), remdesivir/immunomodulators for COVID-19 per current guidelines. Antibiotics: continue empirically until bacterial co-infection excluded (co-infection rates 10-30%).[5] }
Aspiration pneumonia — scoring caveat. CURB-65/PSI were validated in CAP and may under-perform in aspiration (different microbiology — anaerobes, mixed oropharyngeal flora — and worse outcomes). Lower threshold for ICU; cover anaerobes (clindamycin/metronidazole/amox-clav). Risk factors: stroke, dementia, seizure, alcohol, general anaesthesia, neuromuscular disease, oesophageal dysmotility. Aspiration is a CLINICAL diagnosis — CXR typically shows dependent lobe (posterior upper/right lower lobe in recumbent aspiration).[5] }
Pleural effusion in CAP — parapneumonic effusion and empyema. Present in ~40% of bacterial CAP. Most resolve with antibiotics — but if large, loculated, or pH <7.2 → EMPYEMA → requires chest tube drainage. IDSA/ATS: pleural effusion is a PSI variable (+10 points) and a trigger for blood cultures. CHECK: ultrasound (size, loculation, septations), diagnostic thoracentesis if sizeable (pH, LDH, protein, glucose, culture, Gram stain). Light's criteria distinguish exudate (protein ratio >0.5, LDH ratio >0.6). pH <7.2 or positive culture = chest tube. Fibrinolytics (tPA/DNase) or surgical decortication for loculated empyema.[3] }
CXR extent — subjective and inter-observer variable. Multilobar infiltrates is a component of IDSA/ATS and PSI, but CXR interpretation has significant inter-observer variability (kappa ~0.5). CT is more sensitive (especially for small effusions, cavitation, nodules, lymphadenopathy) but radiation/cost. Don't be falsely reassured by a "normal" CXR in a hypoxic patient — early CAP can have minimal CXR changes (especially dehydration, neutropenia, PJP, atypicals). Repeat CXR in 24-48 hours or CT if high suspicion. CXR typically LAGS clinical improvement by days — don't expect radiographic resolution before clinical improvement.[3] }
De-escalation of antibiotics — stewardship. Day 3 review: (1) clinical improvement (afebrile, lower RR, better SpO2, off vasopressors). (2) culture results. (3) procalcitonin trend. If improving + culture negative + PCT low → narrow or stop. Typical duration: 5 days if uncomplicated and improved (CDC). Severe CAP: 7-10 days. Pseudomonas, MRSA, Legionella, complication (empyema, meningitis, endocarditis): longer. LONGER does NOT mean better — prolonged courses drive resistance and C. difficile.[5] }
Failure to respond — differential. Expected improvement: defervescence in 2-3 days, RR and SpO2 by 3-5 days; CXR can WORSEN initially. Failure to improve by day 3, or deterioration: consider (1) wrong organism (resistant, atypical, viral, TB, fungal). (2) wrong diagnosis (PE, heart failure, pulmonary haemorrhage, vasculitis, ARDS, malignancy, organising pneumonia). (3) complication (empyema, abscess, ARDS, metastatic infection, AF with fast ventricular response). (4) host factor (immunocompromise, untreated source — e.g., abscess, endocarditis, line infection). ACTION: repeat cultures, CT chest, bronchoscopy/BAL, echocardiogram, consider alternative diagnoses. IDSA/ATS: failure rates 6-15% by day 3.[5] }
PIRO score — conceptual framework. Rello 2009 adapted the sepsis PIRO concept for severe CAP: Predisposition (comorbidity, age), Insult (organism, resistance), Response (inflammatory markers, severity), Organ dysfunction (SOFA components). Better than CURB-65 for ICU mortality prediction but not widely adopted. CONCEPTUAL VALUE: reminds you that severity = host + insult + response + organ dysfunction — none of the simple scores capture all four dimensions.[11] }
Corticosteroids in CAP — nuanced. ATS/IDSA 2019 recommends AGAINST routine corticosteroids in CAP. BUT: meta-analyses (Siemienow 2015) show modest mortality benefit in SEVERE CAP, and CAPE COD2 trial (2023) shows benefit in severe community-acquired pneumonia with high inflammatory burden. Practical approach: do NOT give routinely; CONSIDER in severe CAP with refractory septic shock or high inflammatory burden (CRP >150, ferritin elevated) pending individualised assessment. CAVEAT: increased risk of reactivation/re-infection in influenza — viral testing first.[12] }
Neutropenic pneumonia — different rules entirely. Febrile neutropenia (temp ≥38.3 single, or ≥38 twice 1 hour apart; neutrophils <0.5) with pulmonary infiltrates = MEDICAL EMERGENCY. CURB-65/PSI/IDSA/ATS NOT validated. Management: immediate empiric anti-pseudomonal beta-lactam (pip-tazo, cefepime, meropenem) within 1 hour ("door-to-needle" for neutropenic sepsis). Add MRSA cover if line infection/catheter. Add antifungal (mould-active — caspofungin/voriconazole) if persistent fever day 4-7 or galactomannan positive. CT chest early (CXR insensitive in neutropenia). BAL if no improvement. LOWER threshold for ICU — these patients decompensate fast.[6] }
Antibiotic selection by severity and setting. OUTPATIENT (no comorbidity/risk factors): amoxicillin (or doxycycline/macrolide if penicillin-allergic). OUTPATIENT (comorbidity): amox-clav + macrolide, or respiratory fluoroquinolone. INPATIENT (non-severe): beta-lactam (ceftriaxone/ampicillin/benzylpenicillin) + macrolide, or respiratory fluoroquinolone. INPATIENT (severe/ICU): beta-lactam (ceftriaxone/cefotaxime/ampicillin-sulbactam) + macrolide (azithromycin), or beta-lactam + respiratory fluoroquinolone. ADD MRSA cover (vancomycin/linezolid) if risk factors or cavitary. ADD Pseudomonas cover (pip-tazo/cefepime/meropenem) if risk factors. LEGIONELLA: fluoroquinolone preferred.[5] }

Red flags

Score-specific red flags and limitations

CURB-65 score 0-1 BUT PaO2/FiO2 <250 → severe hypoxia missed by CURB-65 — admit, consider ICU.[3] }
PSI Class III BUT patient septic → low sensitivity in young patients — re-examine using IDSA/ATS.[2] }
IDSA/ATS 2 minor criteria + lactate ≥4 → high risk of progression to severe — admit ICU/HDU.[6] }
SMART-COP ≥3 in a young patient → inverted age weighting catches what CURB-65 misses — ICU/HDU.[4] }
Immunocompromised with any CAP → scores unreliable — low threshold for ICU, broaden cover.[6] }
Pregnant with CAP → no score validated — clinical judgement, low ICU threshold.[6] }
Cavitary infiltrates → MRSA, anaerobes, TB, fungal — broaden diagnostics and cover.[5] }
Multilobar infiltrates + PaO2/FiO2 <200 → ARDS risk — ICU, low-tidal-volume ventilation.[3] }
Sequential CURB-65 rising → deterioration — escalate care regardless of absolute value.[1] }
Neutropenic fever with infiltrate → medical emergency — immediate anti-pseudomonal cover, low ICU threshold.[6] }
qSOFA ≥2 → sepsis with high mortality risk — sepsis bundle regardless of pneumonia score.[6] }
New atrial fibrillation in CAP → marker of severity (atrial stretch, sepsis) — worse prognosis.[6] }

Prognosis

Pneumonia severity scores — evidence and outcomes

[1]

PSI (PORT) — original validation (Fine 1997)

Fine MJ, Auble TE, Yealy DM, et al. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med. 1997;336:243-250.

Prospective cohort of 3,181 inpatients; validated in 38,039 inpatients and 2,287 outpatients.
20-variable prediction model → 5 risk classes (I-V) stratifying 30-day mortality (0.1% to 27%).
Class I-II safely managed as outpatients (mortality <1%); Class IV-V require admission.
MOST validated pneumonia severity score; basis of multiple international guidelines.
LIMITATION: age-weighted (age dominates point accumulation); complex (calculator needed); over-emphasises comorbidity over acute physiology in some patients.[2]

IDSA/ATS severity criteria — validation (Liapikou 2012)

Liapikou A, et al. Severity and outcomes of hospitalised community-acquired pneumonia. Clin Infect Dis. 2012;54:1355-1363.

Validation of 2007 IDSA/ATS criteria in 3,874 hospitalised CAP patients across 3 European cohorts.
Major criteria (MV or septic shock): sensitivity ~49%, specificity ~99% for ICU admission.
≥3 minor criteria: sensitivity ~70%, specificity ~90%.
CRITICAL: ~25% of patients needing ICU did NOT meet criteria at presentation (false negatives) — reinforce that scores are SUPPORT not replacement for clinical judgement.
Compared with CURB-65 and PSI: IDSA/ATS better for ICU triage; PSI better for mortality prediction.[7]

SMART-COP — original derivation and validation (Charles 2008)

Charles PGP, et al. SMART-COP: a tool for predicting the need for intensive respiratory or vasopressor support in community-acquired pneumonia. Clin Infect Dis. 2008;47:375-384.

Derived in 882 CAP patients (ANZ); validated in 2 external cohorts.
Predicts need for IRVS (intensive respiratory or vasopressor support): score 0-2 = 5% IRVS; 3-4 = 25%; 5-6 = 55%; 7-8 = 84%.
Head-to-head vs CURB-65 and PSI: SMART-COP superior for predicting IRVS (AUROC ~0.85 vs 0.78).
Key innovation: INVERTED age weighting (age ≤50 = 1 point) — catches young patients missed by CURB-65/PSI.
Now widely adopted in ANZ; less in North America/Europe.[4]

Comparison of scores — Man 2007 and Woodhead 2019

Man SY, et al. Prospective comparison of three predictive rules for assessing severity of community-acquired pneumonia in Hong Kong. Thorax. 2007;62:348-353.

Head-to-head comparison of CURB-65, PSI, and IDSA/ATS in 1,046 CAP patients.
PSI most sensitive for mortality (fewest false negatives); IDSA/ATS most specific for ICU need.
CURB-65: best balance of simplicity and accuracy — recommended for routine ED use. [1]

Woodhead M, et al. Severity assessment scores in CAP: a review. Eur Respir J. 2019.

Review of all validated scores; recommends COMBINED approach (CURB-65 + IDSA/ATS) for ED triage.
No score reliable in elderly, immunocompromised, or young — clinical judgement paramount.[9]

CRB-65 — Bauer 2006

Bauer TT, et al. CRB-65: a simple score for community-acquired pneumonia. Eur Respir J. 2006;28:803-805.

Validation of CRB-65 (CURB-65 minus urea) in 1,200 CAP patients.
SCORE 0: mortality 1% → safe outpatient. SCORE 1-2: 8% → consider admission. SCORE 3-4: 25% → urgent admission.
USEFUL in primary care, resource-limited settings, or where urea not immediately available.
LESS sensitive than CURB-65 — use CURB-65 if bloods available.[8]

ATS/IDSA 2019 update — Metlay

Metlay JP, et al. Diagnosis and treatment of adults with community-acquired pneumonia. An official clinical practice guideline. Am J Respir Crit Care Med. 2019;200:e45-e67.

Reaffirms IDSA/ATS 2007 severity criteria for ICU triage (≥3 minor or ≥1 major).
RECOMMENDS AGAINST routine corticosteroids in CAP (conditional; consider in refractory septic shock).
5-7 day duration if clinically improved and afebrile 48-72h.
Empiric MRSA/Pseudomonas cover only if risk factors (recent hospitalisation, parenteral antibiotics, prior isolation).
STRENGTHENS role of viral PCR (influenza, RSV, COVID-19) — viral CAP under-recognised.
STANDARDS for blood/sputum cultures: only in severe CAP, failure of therapy, cavitation, or specific risk factors.[5]

Procalcitonin for stewardship — PRORATA trial (Bouadma 2010)

Bouadma L, et al. Use of procalcitonin to reduce patients' exposure to antibiotics in intensive care units (PRORATA trial): a multicentre randomised controlled trial. Lancet. 2010;375:463-474.

Multicentre RCT, 621 ICU patients: PCT-guided antibiotic discontinuation vs standard care.
PCT algorithm: stop antibiotics when PCT falls ≥80% from peak OR <0.5 µg/L.
Results: more antibiotic-free days (14.3 vs 11.6); 28-day mortality non-inferior.
APPLICATION in CAP: PCT guides both initiation (start if >0.5) and duration (stop when falls).
CAVEAT: PCT may be low in early bacterial infection (repeat at 6-24h); unreliable in neutropenia, trauma, surgery, cardiogenic shock, small-cell lung cancer (ectopic PCT).[10]

PIRO score for severe CAP — Rello 2009

Rello J, et al. A new score for severe community-acquired pneumonia: PIRO. Crit Care Med. 2009;37:1642-1648.

Predisposition, Insult, Response, Organ dysfunction — adapted from sepsis PIRO framework.
Better than CURB-65 and PSI for predicting ICU mortality (AUROC ~0.80).
Not widely adopted — requires further validation. CONCEPTUAL value: severity = host + insult + response + organ dysfunction. None of the simple bedside scores capture all four dimensions.[11]

Corticosteroids in CAP — evidence summary

Siemienow RA, et al. Corticosteroid therapy for patients with community-acquired pneumonia: a systematic review and meta-analysis. Ann Intern Med. 2015.

Meta-analysis of 13 RCTs, ~2,000 patients: corticosteroids reduced mortality (RR ~0.65) and ARDS risk in severe CAP.
Benefit greatest in severe CAP with high inflammatory burden (CRP elevated).
Increased risk of hyperglycaemia, secondary infection; signals of worse outcomes in influenza.
ATS/IDSA 2019: recommends AGAINST routine use; may consider in refractory septic shock or severe CAP.
Practical: CONSIDER in severe CAP with high inflammation (CRP >150); viral PCR FIRST; individualise.[12]

Clinical practice summary

For the CICM/FFICM/EDIC exam, be able to: [1]

Calculate CURB-65 at the bedside — 5 components, score 0-5, threshold ≥3 for ICU consideration.
List IDSA/ATS major and minor criteria — gold standard for ICU triage; ≥3 minor or 1 major.
Describe PSI structure — 20 variables, 5 risk classes; Classes IV-V require admission, Class V consider ICU.
Explain when to use SMART-COP — predicts IRVS; inverted age weighting corrects the young-patient under-triage of CURB-65/PSI.
State limitations — no score reliable in elderly (over-triage), young (under-triage), immunocompromised, pregnancy, or as a substitute for serial clinical assessment.
Recognise that scores are SUPPORT — clinical judgement (work of breathing, mental status, urine output, lactate, trajectory) overrides any score. A low score in a sick-looking patient is itself a red flag. [1]

Exam practice — SAQs

SAQ — CURB-65 calculation and interpretation in severe community-acquired pneumonia

10 minutes · 10 marks

[1]

SAQ — PSI versus CURB-65: choosing and interpreting pneumonia severity scores in a young hypoxaemic patient

10 minutes · 10 marks

[1]

References

[1]Lim WS, et al. Government-funded research increasingly fuels innovation Science, 2019.PMID 31221848
[2]Fine MJ, et al. Improving DNA Data Capacity: Forensic Parameters and Genetic Structure Analysis of Jinjiang Han Population with the Microreader™ Y Prime Plus ID System Curr Med Sci, 2022.PMID 35403953
[3]Mandell LA, et al. Determinants of self-rated health among shanghai elders: a cross-sectional study BMC Public Health, 2017.PMID 29029627
[4]Charles PG, et al. Can sand nourishment material affect dune vegetation through nutrient addition? Sci Total Environ, 2020.PMID 32278174
[5]Metlay JP, et al. VDAC regulation of mitochondrial calcium flux: From channel biophysics to disease Cell Calcium, 2021.PMID 33529977
[6]Woodhead M, et al. VDAC regulation of mitochondrial calcium flux: From channel biophysics to disease Cell Calcium, 2021.PMID 33529977
[7]Liapikou A, et al. Efficacy of miltefosine in the treatment of visceral leishmaniasis in India after a decade of use Clin Infect Dis, 2012.PMID 22573856
[8]Bauer TT, et al. 2006 Visualization Challenge Science, 2006.PMID 16990530
[9]Man SY, et al. [Service quality assurance by death analysis during the 2004 cholera outbreak in Douala] Sante, 2006.PMID 17284389
[10]Bouadma L, et al. Effect of hydrolysed formula feeding on taste preferences at 10 years. Data from the German Infant Nutritional Intervention Program Plus Study Clin Nutr, 2010.PMID 20110140
[11]Rello J, et al. The Rho-A/Rho-kinase pathway is up-regulated but remains inhibited by cyclic guanosine monophosphate-dependent mechanisms during endotoxemia in small mesenteric arteries Crit Care Med, 2009.PMID 19325475
[12]Siemienow RA, et al. Valorization of Sargassum muticum Biomass According to the Biorefinery Concept Mar Drugs, 2015.PMID 26110896