CAP Etiology
Streptococcus pneumoniae (most common overall, rust-colored sputum); Mycoplasma pneumoniae (young adults/military recruits; cold agglutinins).
CURB-65 Criteria
Confusion, Urea > 20, Resp rate ≥ 30, BP < 90/60, Age ≥ 65; score 0–1 = outpatient; 2 = inpatient; ≥ 3 = ICU evaluation.
Legionella Pneumophila
Severe pneumonia + high fever, diarrhea/GI symptoms, hyponatremia, and elevated liver enzymes; diagnosed by urinary antigen.
Pneumocystis jirovecii (PJP)
CD4 < 200 in HIV; bilateral interstitial perihilar ground-glass infiltrates; elevated LDH; first-line therapy & prophylaxis: TMP-SMX.
Pneumonia Classification & Empirical Therapy
| Pneumonia Subtype | Common Etiologies | First-Line Outpatient / Inpatient Regimen | High-Yield Clinical Clues |
|---|---|---|---|
| Outpatient CAP (Healthy) | S. pneumoniae, M. pneumoniae, C. pneumoniae | Amoxicillin 1 g TID OR Doxycycline 100 mg BID (Macrolides only if local resistance < 25%) | Abrupt onset fever, productive cough, pleuritic chest pain; lobar consolidation on CXR |
| Outpatient CAP (Comorbidities) | S. pneumoniae, H. influenzae, Moraxella, Atypicals | Augmentin + Azithromycin (or Doxycycline) OR Respiratory Fluoroquinolone (Levofloxacin/Moxifloxacin) | Patients with COPD, diabetes, heart failure, or chronic renal disease |
| Inpatient CAP (Non-ICU) | S. pneumoniae, Legionella, enterics | Ceftriaxone + Azithromycin OR Levofloxacin monotherapy | IV antibiotics initiated within 4 hours of emergency department arrival |
| Hospital-Acquired (HAP / VAP) | Pseudomonas aeruginosa, MRSA, enterobacter | Antipseudomonal beta-lactam (Cefepime / Zosyn / Meropenem) + Anti-MRSA (Vancomycin / Linezolid) | Onset > 48 hours following hospital admission or endotracheal intubation |
OMM Board Correlate: Pulmonary Lymphatics & Rib Raising
- Pulmonary Sympathetics: Originates from T2–T7. Sympathetic hyperactivity causes thick, tenacious secretions and bronchodilation. Rib raising normalizes sympathetic drive and thins bronchial secretions.
- Chapman Reflexes: Anterior lung points in 3rd and 4th intercostal spaces near sternum; posterior points between T3–T4 and T4–T5 transverse processes.
- Thoracic Pump Technique: Rhythmic compression of the rib cage during exhalation followed by abrupt release enhances thoracic duct lymphatic flow, mobilizes immune cells, and reduces pulmonary edema.
Board Traps & Common Distractors
- In patients with severe PJP pneumonia (PaO2 < 70 mmHg or A-a gradient ≥ 35 mmHg on ABG), ALWAYS initiate adjuvant corticosteroids (IV Prednisone) BEFORE or concurrently with TMP-SMX to prevent fulminant inflammatory respiratory collapse caused by dying organisms.
- Klebsiella pneumoniae classically presents with 'currant jelly' thick blood-tinged sputum and cavitary right upper lobe lesions in individuals with alcohol use disorder.
- Never use Daptomycin for pulmonary infections; it is inactivated by pulmonary surfactant.