Acute Pharyngitis (Adult)

1. Overview

Acute Pharyngitis is acute inflammation of the pharynx and/or tonsils, characterized by sore throat as the predominant symptom. It represents one of the most common presentations in emergency and primary care, accounting for approximately 12 million ambulatory visits annually in the United States. [1]

The clinical significance of pharyngitis lies in the critical diagnostic challenge: 80-90% of cases are viral and self-limited, yet 5-15% in adults are caused by Group A β-Hemolytic Streptococcus (GABHS, Streptococcus pyogenes), which requires antibiotic treatment to prevent suppurative complications (peritonsillar abscess, retropharyngeal abscess) and non-suppurative sequelae (Acute Rheumatic Fever, Post-Streptococcal Glomerulonephritis). [2]

The 2020s diagnostic paradigm emphasizes clinical decision rules (Centor, FeverPAIN) to guide testing rather than empiric treatment. The Rapid Antigen Detection Test (RADT) is the primary diagnostic tool, with throat culture reserved for negative RADT in high-risk scenarios. Management focuses on antibiotic stewardship to reduce unnecessary prescribing, which remains at 60% in many systems despite most cases being viral. [3]

2. Epidemiology

The Viral Predominance

• 80-90% of adult pharyngitis is viral: Rhinovirus, Coronavirus, Adenovirus, Influenza, and EBV (Infectious Mononucleosis).
• GABHS accounts for only 5-15% in adults, rising to 20-30% in children. [4]

Peak Seasons

• Winter/Spring: Peak for GABHS and respiratory viruses.
• Late Summer/Early Autumn: Enterovirus (Coxsackie A → Herpangina).

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3. Aetiology & Pathophysiology

⚠️ THE VIRAL vs. BACTERIAL DISTINCTION

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GABHS Pathophysiology

1. Adherence: M protein on the streptococcal surface binds to pharyngeal epithelium.
2. Toxin Release: Streptococcal pyrogenic exotoxins (SPEs) trigger the host immune response.
3. Local Inflammation: Activation of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) causes erythema, oedema, and exudate formation.
4. Systemic Response: Fever and constitutional symptoms driven by cytokine storm.
5. Molecular Mimicry: In untreated cases, cross-reactive antibodies against streptococcal M protein can target heart valves (ARF) or glomerular basement membrane (PSGN). [5, 6]

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4. Clinical Presentation

Classic GABHS Pharyngitis (The "5 Features")

1. Fever: 38°C (100.4°F)
2. Tonsillar exudate: White/yellow patches
3. Tender anterior cervical lymphadenopathy: Jugulodigastric nodes
4. Absence of cough: Key differentiator from viral
5. Sudden onset: < 24 hours

Viral Pharyngitis Features

• Cough, rhinorrhea, conjunctivitis: "The cold" complex
• Hoarseness: Suggests laryngitis (viral)
• Diffuse erythema without exudate: Non-specific viral inflammation
• Diarrhea: Adenovirus, Enterovirus

Red Flag Presentations

[7, 8]

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5. Investigations

Clinical Decision Rules: Centor and FeverPAIN

Modified Centor Criteria (McIsaac Score)

Score Interpretation:

[9]

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FeverPAIN Score

Score Interpretation:

[10]

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Laboratory Testing

1. Rapid Antigen Detection Test (RADT)

• Sensitivity: 70-90% (varies by manufacturer)
• Specificity: 95%
• Turnaround: 5-10 minutes
• Action: Positive = Treat. Negative + High Clinical Suspicion (Centor ≥3) = Send throat culture. [11]

2. Throat Culture

• Gold Standard: Sensitivity 95%, Specificity 95%
• Limitation: 24-48 hour delay
• Use: Backup for negative RADT in high-risk scenarios (history of ARF, recurrent pharyngitis, outbreak setting).

3. Monospot Test (Heterophile Antibody Test)

• Use: If EBV suspected (posterior cervical LAD, splenomegaly, palatal petechiae)
• Sensitivity: 70-90% (lower in first week)
• False Negatives: Early infection (< 1 week), children < 4 years.

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6. Management

1. Viral Pharyngitis (The 80-90% Majority)

Supportive Care Only:

• Analgesia: NSAIDs (Ibuprofen 400mg PO TDS) or Paracetamol (1g PO QDS)
• Fluids: Encourage hydration
• Rest: Symptom-driven
• Avoid: Antibiotics are not indicated. [12]

Corticosteroids (Adjunctive):

• Evidence: Cochrane review (2012) showed corticosteroids (Dexamethasone 10mg IM or Prednisolone 60mg PO) provide modest symptom relief (pain reduction 6 hours earlier).
• Use: Reserved for severe pain impairing oral intake. [13]

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2. GABHS Pharyngitis: Antibiotic Therapy

Goals of Treatment:

1. Prevent Acute Rheumatic Fever (ARF)
2. Reduce suppurative complications (peritonsillar abscess, retropharyngeal abscess)
3. Shorten symptom duration (by ~1 day)
4. Reduce transmission

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First-Line: Penicillin V

Rationale: GABHS has never developed penicillin resistance. Penicillin V remains the gold standard. [14]

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Penicillin Allergy

Note: Macrolide resistance (Erythromycin, Azithromycin) is 5-10% in the UK/USA, but 30% in Asia. Use with caution. [15]

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3. Delayed Prescribing Strategy

Concept: Provide antibiotic prescription at initial visit but instruct patient to only fill if symptoms worsen or do not improve within 3 days.

Evidence: Cochrane review (2017) showed delayed prescribing reduces antibiotic use by 40% without increased complications. [16]

Indication: Centor 2-3, FeverPAIN 2-3, or negative RADT with patient preference for "safety net".

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4. Avoid Amoxicillin in Suspected EBV

The Mononucleosis Trap:

• 80-100% of patients with EBV who receive amoxicillin or ampicillin develop a diffuse maculopapular rash.
• Mechanism: T-cell mediated hypersensitivity reaction (not true penicillin allergy).
• Action: If EBV suspected (palatal petechiae, splenomegaly, posterior cervical LAD), perform Monospot test before prescribing penicillin. [17]

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7. Complications

Suppurative Complications

[18, 19]

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Non-Suppurative Complications (Post-GABHS)

1. Acute Rheumatic Fever (ARF)

• Incidence: < 1% in developed nations (higher in Aboriginal populations)
• Latency: 2-3 weeks post-GABHS infection
• Jones Criteria: Major (carditis, polyarthritis, chorea, erythema marginatum, subcutaneous nodules) + Minor (fever, arthralgia, elevated ESR/CRP)
• Prevention: Penicillin treatment within 9 days of symptom onset reduces ARF risk by 70%. [20]

2. Post-Streptococcal Glomerulonephritis (PSGN)

• Incidence: 5-10% in endemic strains (serotype M12, M49)
• Latency: 10-14 days post-GABHS
• Presentation: Haematuria, oedema, hypertension
• Note: Antibiotics do NOT prevent PSGN (only ARF). [21]

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8. Evidence: Landmark Trials

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9. Single Best Answer (SBA) Questions

Question 1

A 28-year-old presents with a 12-hour history of severe sore throat and fever of 39°C. Examination reveals tonsillar exudates and tender anterior cervical lymphadenopathy. No cough. What is the most appropriate immediate action?

• A) Prescribe Penicillin VK 500mg PO BID for 10 days

• B) Perform a Rapid Antigen Detection Test (RADT)

• C) Prescribe supportive care and delayed antibiotic prescription

• D) Arrange throat culture

• E) Prescribe Amoxicillin 1g PO once daily for 10 days

• Answer: B. The patient has a Centor score of 4 (fever, exudate, LAD, no cough) + age 15-44 (0 points) = Total 4. At this score, GABHS probability is 43-52%, warranting RADT to confirm diagnosis before empiric treatment. RADT positive → treat; RADT negative → consider throat culture.

Question 2

A 35-year-old presents with sore throat, fever, and tonsillar exudates. RADT is positive for GABHS. The patient reports a "rash" reaction to penicillin 10 years ago (non-severe). What is the most appropriate antibiotic?

• A) Penicillin VK (safe to use)

• B) Cephalexin 500mg PO BID for 10 days

• C) Azithromycin 500mg day 1, then 250mg daily for 4 days

• D) Clindamycin 300mg PO TID for 10 days

• E) No antibiotic (supportive care only)

• Answer: B. Non-severe penicillin allergy (rash) has a low risk of cross-reactivity with cephalosporins (< 1-2%). Cephalexin is the preferred alternative. Azithromycin/Clindamycin are reserved for severe (anaphylaxis) allergy.

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10. Viva Scenario: The "Negative RADT" Dilemma

Examiner: "A 30-year-old presents with a Centor score of 4. RADT is negative. What is your next step?"

Candidate:

1. Recognition: A Centor score of 4 carries a 43-52% pre-test probability of GABHS. However, RADT sensitivity is only 70-90%, meaning there is a 10-30% false negative rate.
2. Action: I would send a throat culture as the gold standard confirmatory test (Sensitivity 95%).
3. Interim Management: I would provide a delayed antibiotic prescription to the patient, instructing them to fill it only if symptoms worsen or do not improve within 3 days, or if the culture returns positive.
4. Rationale: This approach balances antibiotic stewardship (avoiding unnecessary treatment) with patient safety (preventing progression to suppurative complications). [22]

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11. Patient Explanation

"Most sore throats are caused by viruses like the common cold, and they get better on their own in 3-5 days. We use a throat swab test to check for a specific bacteria called 'Strep' that needs antibiotics. If the test is positive, we'll give you antibiotics to prevent rare complications like rheumatic fever, which can affect the heart. If the test is negative, you likely have a viral infection, and antibiotics won't help. I recommend pain relief like Ibuprofen, plenty of fluids, and rest. Come back if you develop trouble breathing, difficulty swallowing, or if symptoms worsen."

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12. References

1. Bisno AL. Acute pharyngitis. N Engl J Med. 2001;344(3):205-211. [PMID: 11172144]
2. Shulman ST, Bisno AL, Clegg HW, et al. Clinical practice guideline for the diagnosis and management of group A streptococcal pharyngitis: 2012 update by the Infectious Diseases Society of America. Clin Infect Dis. 2012;55(10):e86-e102. [PMID: 22965026]
3. Luo R, Sickler J, Vahidnia F, et al. Diagnosis and management of group A streptococcal pharyngitis in the United States, 2011-2015. BMC Infect Dis. 2019;19(1):193. [PMID: 30808305]
4. Mustafa Z, Ghaffari M. Diagnostic methods, clinical guidelines, and antibiotic treatment for group A streptococcal pharyngitis: a narrative review. Front Cell Infect Microbiol. 2020;10:563627. [PMID: 33178623]
5. Wessels MR. Streptococcal pharyngitis. N Engl J Med. 2011;364(7):648-655. [PMID: 21323542]
6. Carapetis JR, Beaton A, Cunningham MW, et al. Acute rheumatic fever and rheumatic heart disease. Nat Rev Dis Primers. 2016;2:15084. [PMID: 27188830]
7. Ebell MH, Smith MA, Barry HC, et al. The rational clinical examination. Does this patient have strep throat? JAMA. 2000;284(22):2912-2918. [PMID: 11147989]
8. Klug TE, Rusan M, Fuursted K, et al. Fusobacterium necrophorum: most prevalent pathogen in peritonsillar abscess in Denmark. Clin Infect Dis. 2009;49(10):1467-1472. [PMID: 19842976]
9. Fine AM, Nizet V, Mandl KD. Large-scale validation of the Centor and McIsaac scores to predict group A streptococcal pharyngitis. Arch Intern Med. 2012;172(11):847-852. [PMID: 22566485]
10. Little P, Hobbs FD, Moore M, et al. PRImary care Streptococcal Management (PRISM) study: development and validation of the FeverPAIN score. Health Technol Assess. 2014;18(6):1-101. [PMID: 24467988]
11. Gerber MA, Shulman ST. Rapid diagnosis of pharyngitis caused by group A streptococci. Clin Microbiol Rev. 2004;17(3):571-580. [PMID: 15258094]
12. Spinks A, Glasziou PP, Del Mar CB. Antibiotics for sore throat. Cochrane Database Syst Rev. 2013;(11):CD000023. [PMID: 24190439]
13. Hayward G, Thompson MJ, Perera R, et al. Corticosteroids as standalone or add-on treatment for sore throat. Cochrane Database Syst Rev. 2012;10:CD008268. [PMID: 23076948]
14. Leung AKC, Lam JM, Barankin B, et al. Group A β-hemolytic streptococcal pharyngitis: an updated review. Curr Pediatr Rev. 2024;21(1):2-17. [PMID: 37534502]
15. Falagas ME, Vouloumanou EK, Matthaiou DK, et al. Effectiveness and safety of short-course vs long-course antibiotic therapy for group A beta hemolytic streptococcal tonsillopharyngitis: a meta-analysis of randomized trials. Mayo Clin Proc. 2008;83(8):880-889. [PMID: 18674472]
16. Spurling GK, Del Mar CB, Dooley L, et al. Delayed antibiotic prescriptions for respiratory infections. Cochrane Database Syst Rev. 2017;9:CD004417. [PMID: 28881007]
17. Cohen JI. Epstein-Barr virus infection. N Engl J Med. 2000;343(7):481-492. [PMID: 10944566]
18. Powell J, Wilson JA. An evidence-based review of peritonsillar abscess. Clin Otolaryngol. 2012;37(2):136-145. [PMID: 22321140]
19. Karkos PD, Asrani S, Karkos CD, et al. Lemierre's syndrome: a systematic review. Laryngoscope. 2009;119(8):1552-1559. [PMID: 19554637]
20. Pellegrino R, Timitilli E, Verga MC, et al. Acute pharyngitis in children and adults: descriptive comparison of current recommendations from national and international guidelines and future perspectives. Eur J Pediatr. 2023;182(12):5259-5273. [PMID: 37819417]

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Last Updated: 2026-01-10 | MedVellum Editorial Team