Clinical meaning
Community-acquired pneumonia (CAP) results from pathogen entry into the lower respiratory tract overwhelming local immune defenses. S. pneumoniae remains the most common typical bacterial cause, producing lobar consolidation with inflammatory exudate filling alveoli. Atypical organisms (Mycoplasma, Chlamydophila, Legionella) cause interstitial inflammation with patchy infiltrates. Hospital-acquired pneumonia (HAP, >= 48 hours after admission) and ventilator-associated pneumonia (VAP, >= 48 hours after intubation) involve more resistant organisms: MRSA, Pseudomonas aeruginosa, Acinetobacter, extended-spectrum beta-lactamase (ESBL) producers. Risk factors for multidrug-resistant (MDR) pathogens include IV antibiotics within 90 days, > 5 days hospitalization, prior MDR colonization, structural lung disease, and immunosuppression. Severity assessment using CRB-65 (outpatient) or CURB-65 and PSI/PORT (inpatient) guides site-of-care and empiric antibiotic decisions.
Diagnosis & workup
Diagnostics & workup: - CXR PA and lateral: consolidation, air bronchograms, pleural effusion, interstitial pattern - CURB-65 score: Confusion, Urea > 7 mmol/L, RR >= 30, BP < 90/60, age >= 65 — score 0-1 outpatient, 2 consider admission, 3-5 ICU/high care - Blood cultures × 2 before antibiotics for moderate-severe CAP and all HAP/VAP - Sputum Gram stain and culture: quality specimen (> 25 PMNs, < 10 squamous/LPF) - Procalcitonin: > 0.25 mcg/L supports bacterial etiology; serial levels guide antibiotic duration - Legionella and pneumococcal urinary antigens for moderate-severe CAP - CT chest if CXR equivocal, complicated effusion suspected, or treatment failure at 48-72 hours - BAL or mini-BAL for VAP diagnosis: quantitative cultures > 10⁴ CFU/mL considered positive