What is Community-Acquired Pneumonia?
Community-acquired pneumonia (CAP) is an acute lower respiratory tract infection acquired outside of hospital or healthcare settings, characterised by new pulmonary infiltrates on chest imaging plus clinical features (fever, cough, dyspnoea, pleuritic chest pain, new consolidation). CAP most commonly caused by Streptococcus pneumoniae (30–40%), followed by atypical pathogens (Mycoplasma, Chlamydophila, Legionella) and respiratory viruses.
Pathophysiology
Bacteria or viruses breach normal pulmonary defence mechanisms (mucociliary clearance, alveolar macrophages, secretory IgA) to establish infection in the alveolar space. Inflammatory exudate — neutrophils, fibrin, red cells — fills alveoli causing consolidation and impaired gas exchange. Systemic inflammatory response drives fever, tachycardia, and leukocytosis. Bacteraemia (15–25% of hospitalised CAP) increases mortality risk significantly.
Clinical Features & Symptoms
- Fever (>38°C) or hypothermia
- Productive cough (purulent sputum)
- Pleuritic chest pain
- Dyspnoea and tachypnoea
- Dullness to percussion, bronchial breathing on auscultation
- Confusion (new onset, especially in elderly — Confusion = 1 CURB-65 point)
- Systemic features: rigors, myalgia, headache (atypical pathogens)
Diagnosis
Clinical diagnosis confirmed by chest X-ray (new consolidation, interstitial infiltrates). Severity stratification by CURB-65 score: Confusion, Urea >7 mmol/L, Respiratory rate ≥30/min, Blood pressure SBP <90 or DBP ≤60 mmHg, Age ≥65. Score 0–1: low severity; 2: moderate; 3–5: severe. Additional investigations: oxygen saturation, blood cultures (hospitalised), sputum culture, urinary pneumococcal and Legionella antigens, COVID-19 PCR.
Current Treatment Guidelines
CURB-65 severity assessment
Class I, Level AScore 0–1: outpatient treatment appropriate. Score 2: hospitalise for IV/oral antibiotics, monitor closely. Score 3–5: hospital admission, consider ICU for score 4–5.
Antibiotics — low severity (CURB-65 0–1)
Class I, Level AAmoxicillin 500 mg–1 g TDS orally for 5 days. Add clarithromycin/doxycycline if atypical pathogen suspected. Avoid fluoroquinolones as first-line (resistance preservation).
Antibiotics — moderate severity (CURB-65 2)
Class I, Level ACo-amoxiclav 625 mg TDS (or amoxicillin + clavulanate) + clarithromycin 500 mg BD. IV if unable to take orals. 5–7 day course.
Antibiotics — severe (CURB-65 3–5)
Class I, Level AIV co-amoxiclav 1.2 g TDS + IV clarithromycin 500 mg BD. If Pseudomonas risk: piperacillin-tazobactam. Levofloxacin monotherapy if penicillin allergy. 7–10 days total.
Supportive care
Class I, Level BOxygen to maintain SpO₂ ≥94% (88–92% if COPD). IV fluids if unable to maintain oral intake. Physiotherapy if significant secretions. VTE prophylaxis in hospitalised patients.
Vaccination
Class I, Level APneumococcal vaccine (PCV13 + PPSV23) in adults ≥65 and those with comorbidities. Influenza vaccination annually. Reduces CAP incidence, hospitalisation, and mortality.
Monitoring & Treatment Targets
Clinical review at 48–72 hours (IV to oral switch if improving). SpO₂ ≥94%. Temperature, HR, RR, CRP at 48h. Discharge when clinically stable and tolerating oral medications. Follow-up CXR at 6 weeks in smokers, elderly, or recurrent CAP to exclude malignancy.
Key Clinical Trials
External Resources
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Frequently Asked Questions
What CURB-65 score requires hospital admission for pneumonia?
A CURB-65 score ≥2 indicates moderate severity and requires hospital-supervised treatment. Scores of ≥3 mandate hospital admission. Scores of 4–5 carry 15–40% 30-day mortality and require consideration of ICU or HDU admission. However, clinical context (SpO₂, social circumstances, comorbidities) should always supplement the score.
What is the first-line antibiotic for community-acquired pneumonia?
For low-severity CAP (CURB-65 0–1): amoxicillin 500 mg–1 g three times daily for 5 days is first-line per BTS and NICE guidelines. If atypical pathogen suspected (younger patient, bilateral changes, extrapulmonary features): add clarithromycin or doxycycline. Fluoroquinolones should be reserved for penicillin allergy or treatment failure.
Medical disclaimer: This content is intended for qualified healthcare professionals and does not constitute medical advice. Always apply clinical judgment and refer to current local guidelines and institutional protocols.