Summary

Community-acquired pneumonia (CAP) is an acute infection of the lung parenchyma acquired outside hospital. Common pathogens include Streptococcus pneumoniae (most common), Haemophilus influenzae, and atypical organisms (Mycoplasma, Legionella). Severity assessment using CURB-65 guides management setting (community, hospital, or ICU). Treatment involves empirical antibiotics targeting typical and atypical pathogens based on severity. BTS guidelines provide the evidence base for UK practice.

Key Facts

• Definition: Acute lower respiratory infection acquired in community
• Incidence: 5-11 per 1,000 adults per year
• Peak Demographics: Elderly, comorbidities
• Pathognomonic: Cough + fever + consolidation on CXR
• Gold Standard Investigation: CXR + severity assessment
• First-line Treatment: Amoxicillin (mild); amoxicillin + macrolide (moderate/severe)
• Prognosis: CURB-65 0-1: less than 3% mortality; CURB-65 3-5: greater than 20%

Clinical Pearls

Severity Pearl: CURB-65 2+ = hospital admission; 3+ = consider ICU.

Atypical Pearl: Add macrolide if moderate-severe for atypical cover.

Duration Pearl: 5 days for mild-moderate CAP is sufficient if responding.

Viva Points

"CAP: S. pneumoniae most common. CURB-65 for severity: 0-1 community, 2 hospital, 3+ ICU. Amoxicillin first-line; add macrolide for moderate-severe. 5 days treatment usually sufficient."

Last Reviewed: 2026-01-01 | MedVellum Editorial Team