Acute infection of lung parenchyma acquired outside hospital. Stratify severity to guide treatment setting and antibiotic choice.
⚠ Red flags
- CURB-65 ≥3 — high mortality; admit
- SpO₂ <90%, RR >30, SBP <90 mmHg
- Multilobar consolidation, large pleural effusion, empyema
- Sepsis or septic shock features
Diagnostic criteria
Clinical
- Cough, fever, pleuritic chest pain, dyspnoea, sputum
- Focal crackles or bronchial breathing on auscultation
Investigations
- CXR: consolidation, infiltrate, ± effusion
- Severity assessment: CURB-65 or CRB-65
Scoring tools
- CURB-65 (Confusion, Urea >7, RR ≥30, BP <90/60, age ≥65)
- CRB-65 (community version, no urea)
- PSI / Pneumonia Severity Index
Investigations
Essential
- CXR (PA)
- FBC, CRP, U&E, LFTs
- Blood cultures ×2 if severe (before antibiotics)
Optional
- Sputum culture and sensitivity
- Legionella + pneumococcal urinary antigens (severe CAP)
- ABG if SpO₂ <94%
- Viral PCR (influenza, SARS-CoV-2) in season
Management
Acute
- O₂ to maintain SpO₂ ≥94% (88–92% if at risk of hypercapnia)
- IV fluids; assess sepsis bundle compliance
- Source review for empyema or abscess if no clinical improvement at 48–72h
Long-term
- Repeat CXR at 6 weeks if persistent symptoms or smoker — exclude underlying malignancy
- Smoking cessation; vaccinations (pneumococcal, influenza)
Non-pharmacological
- Adequate hydration, rest, sit up to aid expansion
- Chest physiotherapy if retained secretions
Pharmacological
| Drug | Dose | Notes |
|---|---|---|
| Amoxicillin | 500 mg PO TDS for 5–7 days | CURB-65 0–1 (mild outpatient). |
| Amoxicillin + clarithromycin | 500 mg TDS + 500 mg BD PO | CURB-65 = 2 (moderate). |
| Co-amoxiclav + clarithromycin | 1.2 g IV TDS + 500 mg IV BD | CURB-65 ≥3 (severe, admit). |
| Levofloxacin | 500 mg PO/IV once daily | Alternative for penicillin allergy. |
| Oseltamivir | 75 mg PO BD for 5 days | Add if confirmed/strongly suspected influenza within 48h of onset. |
Monitoring
- Re-assess at 48–72h: temperature, oxygenation, CRP trend
- CRP fall <50% by 48h suggests inadequate response
- Repeat CXR at 6 weeks if smoker, age >50, or persistent symptoms
Referral criteria
- CURB-65 ≥3 — admit
- Failure to respond at 72h — review for resistance, empyema, atypical pathogen
- Recurrent CAP (>1 episode/year) — investigate for bronchiectasis, immunodeficiency, malignancy
Complications
- Parapneumonic effusion / empyema
- Lung abscess
- Sepsis and ARDS
- Atrial fibrillation (esp. elderly)
Special populations
- Pregnancy
- Avoid fluoroquinolones and tetracyclines. Amoxicillin and erythromycin generally safe.
- Renal impairment
- Adjust amoxicillin and ciprofloxacin doses. Monitor co-amoxiclav for crystalluria.
- Hepatic impairment
- Co-amoxiclav cholestasis risk; choose alternatives in active liver disease.
- Elderly
- Atypical presentation common (delirium, falls). Lower threshold for admission and CXR.
- Paediatric
- Amoxicillin first-line for paediatric CAP. Consider macrolide for atypical pathogens >5y.