Community‑Acquired Pneumonia (CAP)
CAP is infection of the pulmonary parenchyma acquired outside hospital or other healthcare settings. In the ED the priorities are rapid recognition, assessment of severity and need for escalation, prompt investigations and timely empirical antibiotics when indicated, with clear disposition, safety‑netting and prevention advice (NICE NG250).
Epidemiology and prognosis
- Incidence in UK adults ~0.5-1% per year; CAP is diagnosed in 5-12% of adults presenting with lower respiratory tract infection and 22-42% of those are admitted.
- Mortality: <1% if treated entirely in the community, >5% for admitted patients and can exceed 30% in ICU.
- Risk of death rises with age (especially >84 years), comorbidity and presence of sepsis.
Pathogens and clinical patterns
- Common bacterial causes: Streptococcus pneumoniae (most frequent), Haemophilus influenzae, Moraxella catarrhalis.
- Staphylococcus aureus: associated with severe disease, post‑influenza infection, intravenous drug use or ICU‑acquired infection.
- Atypical organisms: Mycoplasma pneumoniae, Legionella pneumophila (may present with systemic features, hyponatraemia, diarrhoea), Chlamydia psittaci (bird exposure), Coxiella burnetii (occupational exposures).
- Viruses: influenza, SARS‑CoV‑2, RSV - can cause primary viral pneumonia or predispose to secondary bacterial infection.
Clinical features and focused history
- Typical features: fever, productive cough, pleuritic chest pain, dyspnoea, rigors, sweats, myalgia.