Community-Acquired Pneumonia (CAP) Management

Community-acquired pneumonia (CAP) is acute infection of the pulmonary parenchyma acquired outside healthcare settings, with annual incidence of 5-11 cases per 1000 adults and mortality rates 1-5% (outpatient) to 20-50% (ICU). Etiology includes Streptococcus pneumoniae (most common, 30-50%), atypical pathogens (Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella pneumophila), Haemophilus influenzae, Staphylococcus aureus (including MRSA, post-influenza), respiratory viruses (influenza, RSV, SARS-CoV-2, parainfluenza), and gram-negative bacteria (Enterobacteriaceae, Pseudomonas in structural lung disease).

Diagnosis requires clinical signs (cough, fever, dyspnea, pleuritic chest pain) plus radiographic infiltrate. Severity assessment uses CURB-65 score (Confusion, Urea >7 mmol/L, Respiratory rate >30, Blood pressure <90/60, age ≥65; 0-1 outpatient, 2 inpatient consideration, ≥3 hospitalize, ≥4 ICU consideration) or Pneumonia Severity Index (PSI) with 5 risk classes. Site-of-care decision incorporates clinical judgment, comorbidities, and social factors. Microbiologic workup is selective: severe CAP requires blood cultures, sputum Gram stain/culture, urine antigens (pneumococcal, Legionella), respiratory virus PCR, and molecular testing.

Empiric antibiotic therapy per 2019 ATS/IDSA guidelines: Outpatient healthy adults: amoxicillin 1 g TID or doxycycline 100 mg BID or macrolide (azithromycin 500 mg day 1, then 250 mg/day or clarithromycin 500 mg BID) only if local pneumococcal macrolide resistance <25%. Outpatient with comorbidities: amoxicillin/clavulanate or cephalosporin + macrolide/doxycycline, OR respiratory fluoroquinolone (levofloxacin 750 mg, moxifloxacin 400 mg). Inpatient non-severe: ceftriaxone or ampicillin/sulbactam + macrolide, OR fluoroquinolone monotherapy. Severe ICU CAP: beta-lactam (ceftriaxone, ampicillin/sulbactam) + macrolide (azithromycin) OR + fluoroquinolone (preferred if Legionella suspected); add MRSA coverage (vancomycin or linezolid) if risk factors; add Pseudomonas coverage (piperacillin/tazobactam, cefepime, meropenem) for bronchiectasis or recent broad-spectrum antibiotics. Duration: 5-7 days for uncomplicated CAP; longer for empyema, lung abscess, or necrotizing pneumonia. Adjuncts: oseltamivir if influenza positive, prone positioning and corticosteroids for severe COVID-19 pneumonia.