Pulmonary Infections: Site of Care, Pathogen, and Isolation
Community-acquired pneumonia
Streptococcus pneumoniae remains the most common pathogen, with atypicals (Mycoplasma, Chlamydia, Legionella) and viruses filling out the list. Severity scoring drives the site of care: CURB-65 (confusion, urea >7 mmol/L, respiratory rate ≥30, blood pressure low, age ≥65) with ≥2 points supports admission. Outpatients without comorbidity receive a beta-lactam plus macrolide, or doxycycline monotherapy where resistance is low; inpatients get a beta-lactam plus macrolide or a respiratory fluoroquinolone.
Tuberculosis
Suspect TB with upper-lobe cavitation, weight loss, and night sweats. Place in a negative-pressure room with N95 respiratory protection, obtain three sputum specimens for acid-fast bacilli, and use nucleic acid amplification for rapid confirmation. Latent infection screening uses interferon-gamma release assay or tuberculin skin test; treatment options include rifampin for 4 months or isoniazid plus rifapentine weekly for 12 weeks. HIV co-infection can produce lower-lobe disease, mediastinal adenopathy, and a falsely negative skin test - a frequent trap.
Immunocompromised hosts
Neutropenic patients with nodular lesions and halo sign need coverage for invasive aspergillosis. Pneumocystis pneumonia presents with ground-glass opacities, elevated LDH, and hypoxemia; add steroids when PaO2 <70 mmHg or the A-a gradient >35. Aspergilloma in a preexisting cavity causes hemoptysis and is treated surgically if recurrent, not with antifungals routinely.
Worked rule
Aspiration pneumonia in a patient with dysphagia: cover anaerobes with ampicillin-sulbactam.