Overview
Lung Abscess
Topic Overview
Summary
Lung abscess is a circumscribed collection of pus within the lung parenchyma, usually resulting from aspiration of oropharyngeal contents or necrotising pneumonia. Classic presentation is subacute illness with productive cough (often foul-smelling sputum), fever, and weight loss. CXR/CT shows cavitating lesion with air-fluid level. Treatment is prolonged antibiotics (typically 4-6 weeks); most resolve without surgery. Drainage may be required for refractory cases.
Key Facts
- Cause: Aspiration (most common), necrotising pneumonia, septic emboli
- Organisms: Often polymicrobial with anaerobes (Bacteroides, Fusobacterium, Peptostreptococcus)
- Presentation: Subacute fever, productive cough, foul sputum, weight loss
- Imaging: Cavity with air-fluid level on CXR/CT
- Treatment: Prolonged antibiotics (4-6 weeks); drainage if refractory
- Prognosis: Most resolve with antibiotics alone
Clinical Pearls
Foul-smelling sputum = anaerobic infection = lung abscess until proven otherwise
Think aspiration in patients with reduced consciousness, dysphagia, or dental disease
Most lung abscesses resolve with antibiotics alone — surgery rarely needed
Why This Matters Clinically
Lung abscess can mimic malignancy and tuberculosis. Recognising the clinical picture and choosing appropriate antibiotics (covering anaerobes) leads to good outcomes. Failure to treat adequately causes empyema and chronic infection.
Visual Summary
Visual assets to be added:
- CXR showing lung abscess with air-fluid level
- CT chest showing cavitating lesion
- Aspiration risk factors diagram
- Lung abscess management algorithm
Epidemiology
Incidence
- Uncommon in the antibiotic era
- Higher in developing countries
- Associated with aspiration risk factors
Demographics
- Middle-aged and elderly
- Male predominance
- Often with comorbidities (alcoholism, stroke, poor dentition)
Risk Factors for Aspiration
| Factor | Mechanism |
|---|---|
| Reduced consciousness | Alcohol, sedation, post-ictal |
| Dysphagia | Stroke, oesophageal disorders |
| Poor dentition/periodontal disease | Anaerobe source |
| GORD | Reflux aspiration |
| Mechanical ventilation | ICU-acquired |
| Immunosuppression | HIV, chemotherapy |
Pathophysiology
Mechanism
- Aspiration of oropharyngeal secretions (most common)
- Bacterial inoculum establishes infection in lung
- Necrotising pneumonia → tissue destruction
- Cavity forms (abscess containing pus and air)
Common Organisms
| Type | Organisms |
|---|---|
| Anaerobes | Bacteroides, Fusobacterium, Peptostreptococcus, Prevotella |
| Aerobes | Streptococcus milleri group, Staphylococcus aureus, Klebsiella |
| Mixed | Often polymicrobial (anaerobes + aerobes) |
Location
- Right lung more common (aspiration — more vertical bronchus)
- Posterior segments of upper lobes (supine aspiration)
- Superior segments of lower lobes
Other Causes
- Necrotising pneumonia (S. aureus, Klebsiella, Streptococcus)
- Septic emboli (endocarditis, IV drug use)
- Bronchial obstruction (tumour → post-obstructive abscess)
Clinical Presentation
Symptoms
Signs
Red Flags
| Finding | Significance |
|---|---|
| Haemoptysis | Erosion into vessel |
| Persistent fever despite antibiotics | Inadequate treatment, drainage needed |
| Large abscess (over 6 cm) | Less likely to resolve with antibiotics alone |
Subacute or chronic illness (days to weeks)
Common presentation.
Productive cough
Common presentation.
Foul-smelling sputum (anaerobes; not always present)
Common presentation.
Fever, night sweats
Common presentation.
Weight loss
Common presentation.
Malaise
Common presentation.
Haemoptysis (occasionally)
Common presentation.
Pleuritic chest pain
Common presentation.
Clinical Examination
General
- Fever
- Weight loss (chronic)
- Clubbing (chronic)
Respiratory
- Reduced breath sounds over abscess
- Bronchial breathing
- Crackles
- Signs of pleural effusion (if empyema)
Oral/Dental
- Poor dentition
- Periodontal disease
Investigations
Blood Tests
| Test | Finding |
|---|---|
| WCC | Elevated |
| CRP | Elevated |
| Anaemia | Chronic disease |
| LFTs, U&E | Baseline |
Sputum
- Culture (aerobic and anaerobic)
- Gram stain
- AFB (exclude TB)
Imaging
| Modality | Findings |
|---|---|
| CXR | Cavity with air-fluid level |
| CT chest | Better defines abscess, excludes underlying malignancy, bronchial obstruction |
Bronchoscopy
- If concern for obstruction (tumour)
- If diagnostic uncertainty
- Obtain samples for culture
Exclude Other Causes
- TB (AFB smear, culture, IGRA)
- Malignancy (CT, bronchoscopy, biopsy)
Classification & Staging
By Aetiology
| Type | Cause |
|---|---|
| Primary | Aspiration in otherwise healthy lung |
| Secondary | Underlying pathology (bronchial obstruction, malignancy, septic emboli) |
By Duration
- Acute: Under 4-6 weeks
- Chronic: Over 6 weeks
By Size
- Small: Under 4 cm
- Large: Over 6 cm (poorer response to antibiotics alone)
Management
Antibiotics — Mainstay
Empirical Regimen (Cover Anaerobes):
| Regimen | Notes |
|---|---|
| Co-amoxiclav | First-line; covers anaerobes and common aerobes |
| Clindamycin | Good anaerobic cover; alternative |
| Metronidazole + amoxicillin | Alternative |
| Piperacillin-tazobactam | Severe or hospital-acquired |
Duration: 4-6 weeks (until resolution clinically and radiologically)
Supportive Care
- Nutritional support
- Physiotherapy (postural drainage)
- Treat underlying cause (dental treatment)
Drainage — If Refractory
| Indication | Approach |
|---|---|
| Failure to improve (5-7 days) | Consider drainage |
| Large abscess (over 6 cm) | Percutaneous drainage |
| Empyema | Chest drain |
Surgery — Rarely Needed
| Indication | Procedure |
|---|---|
| Massive haemoptysis | Lobectomy |
| Failure of antibiotics + drainage | Lobectomy |
| Underlying malignancy | Resection |
Complications
Of Lung Abscess
- Empyema (rupture into pleural space)
- Bronchopleural fistula
- Haemoptysis (erosion into vessel)
- Chronic abscess
- Aspergilloma (in chronic cavity)
Of Treatment
- Antibiotic side effects
- Procedure complications (drain insertion)
Prognosis & Outcomes
Prognosis
- Most resolve with antibiotics (over 85%)
- Mortality low (under 5%) in primary abscess
- Higher mortality in secondary abscess (underlying malignancy, immunosuppression)
Factors Associated with Poor Outcome
- Large abscess (over 6 cm)
- Underlying malignancy
- Immunosuppression
- Necrotising organisms (S. aureus, Klebsiella)
Evidence & Guidelines
Key Guidelines
- No specific national guideline
- Management based on consensus and case series
Key Evidence
- Prolonged antibiotics (4-6 weeks) are effective
- Drainage indicated if no improvement by 7-10 days
Patient & Family Information
What is a Lung Abscess?
A lung abscess is a pocket of pus inside the lung, usually caused by infection. It often happens when germs from the mouth are breathed into the lungs.
Symptoms
- Cough with bad-smelling phlegm
- Fever and night sweats
- Weight loss
- Feeling tired
Treatment
- Antibiotics for several weeks
- Sometimes a tube to drain the pus
- Rarely, surgery
What Happens Next?
- Most people recover fully with antibiotics
- Dental care may help prevent future infections
Resources
References
Key Studies
- Kuhajda I, et al. Lung abscess-etiology, diagnostic and treatment options. Ann Transl Med. 2015;3(13):183. PMID: 26366400
- Bartlett JG. The role of anaerobic bacteria in lung abscess. Clin Infect Dis. 2005;40(7):923-925. PMID: 15824979
Reviews
- Moreira Jda S, et al. Lung abscess: analysis of 252 consecutive cases diagnosed between 1968 and 2004. J Bras Pneumol. 2006;32(2):136-143. PMID: 17273583