Pulmonary Infections

Pneumonia Basics & CAP - The Common Cough Chaos

Pneumonia: Inflammation of lung parenchyma. Classification:

• CAP: Community-Acquired (outside hospital or <48h admission).
• HAP: Hospital-Acquired (≥48h post-admission).
• VAP: Ventilator-Associated (>48-72h post-intubation).

Community-Acquired Pneumonia (CAP):

• Common Pathogens:
  • Streptococcus pneumoniae (most common)
  • Haemophilus influenzae
  • Moraxella catarrhalis
  • Atypicals: Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella spp.

📌 CURB-65 (CAP Severity):

• Confusion (new)
• Urea >7 mmol/L
• RR ≥30/min
• BP (SBP <90 mmHg or DBP ≤60 mmHg)
• Age ≥65 years

⭐ The most common bacterial cause of Community-Acquired Pneumonia (CAP) globally is Streptococcus pneumoniae.

Nosocomial Pneumonias & Complications - Hospital Hazards & Aftermath

• Definitions:
  • Hospital-Acquired Pneumonia (HAP): Develops >48h post-admission.
  • Ventilator-Associated Pneumonia (VAP): Develops >48-72h post-intubation.
• Risk Factors: Mechanical ventilation, prolonged stay, immunosuppression, prior antibiotics.
• Common Pathogens: Pseudomonas aeruginosa, MRSA, Acinetobacter baumannii, Klebsiella pneumoniae.
• Complications:
  • Pleural Effusion: Fluid in pleural space.
  • Empyema: Pus in pleural space.
  • Lung Abscess: Necrotic lung cavity; air-fluid level.
• Treatment: Empiric broad-spectrum antibiotics, then de-escalation based on cultures.
• 📌 VAP Prevention Bundle: HOB elevation 30-45°, daily sedation interruption, oral chlorhexidine, DVT/PUD prophylaxis.

⭐ Ventilator-Associated Pneumonia (VAP) occurring >5 days after intubation (late-onset) is more likely caused by multi-drug resistant (MDR) pathogens.

Tuberculosis - The Great White Plague Persists

• Primary TB: Asymptomatic; Ghon focus (peripheral lesion + hilar LN), Ghon complex (calcified), Ranke complex (fibrocalcified).

• Post-primary (Reactivation) TB: Symptomatic; apical cavities/infiltrates.

• Clinical Features: Cough >2wks, fever, night sweats, weight loss, hemoptysis.

• Diagnosis:

  • Sputum AFB smear (ZN stain).
  • Culture: LJ medium (gold standard, 4-8wks).
  • CBNAAT/GeneXpert: Preferred initial test (detects TB & Rif-R in ~2hrs).
  • TST (Mantoux): ≥10mm induration significant (≥5mm in HIV+). IGRA.
  • CXR: Apical infiltrates/cavities, miliary TB.

• NTEP Diagnostic Algorithm for PTB: (CBNAAT is central)

• First-line ATT: 📌 RIPE (Isoniazid, Rifampicin, Pyrazinamide, Ethambutol)

  Drug	Standard Adult Dose	Key Side Effects (📌)
  Isoniazid (H)	5mg/kg (max 300mg)	Peripheral Neuropathy (+B6), Hepatitis
  Rifampicin (R)	10mg/kg (max 600mg)	Orange secretions, Hepatitis, Flu-like
  Pyrazinamide (Z)	25mg/kg	Hyperuricemia (gout), Hepatitis
  Ethambutol (E)	15mg/kg	Optic neuritis (R-G color blindness)

• Treatment (NTEP): Intensive Phase (IP): 2 months HRZE. Continuation Phase (CP): 4 months HR/HRE.

⭐ Under India's National Tuberculosis Elimination Program (NTEP), CBNAAT is the preferred initial diagnostic test for all presumptive pulmonary TB cases, as it detects M. tuberculosis and rifampicin resistance rapidly within hours.

Special Pneumonias - The Unusual Suspects

Atypical Pneumonias:

• Pneumocystis jirovecii Pneumonia (PJP):
  • In HIV with CD4 <200 cells/μL.
  • 📌 Triad: Dry cough, Dyspnea, Fever in immunocompromised.
  • Features: Insidious dyspnea, ↑LDH, diffuse bilateral interstitial infiltrates.
  • Rx & Prophylaxis: TMP-SMX.
• Aspergillosis:
  • Allergic Bronchopulmonary Aspergillosis (ABPA).
  • Aspergilloma (fungus ball in pre-existing cavity).
  • Invasive aspergillosis (immunocompromised).
• Viral Influenza:
  • Abrupt onset, fever, myalgia, cough.
  • Rx: Oseltamivir if early.

⭐ Pneumocystis jirovecii pneumonia (PJP) classically presents in HIV-infected individuals with a CD4 count below 200 cells/μL with progressive dyspnea, non-productive cough, fever, and significantly elevated serum LDH levels.

High‑Yield Points - ⚡ Biggest Takeaways

• S. pneumoniae is the most common cause of CAP; CURB-65 assesses severity.
• Atypical pneumonia: Mycoplasma (cold agglutinins), Legionella (hyponatremia, GI symptoms).
• Tuberculosis: Post-primary TB often shows apical cavitary lesions; CBNAAT for diagnosis.
• HAP/VAP: Key pathogens include Pseudomonas aeruginosa and MRSA.
• PJP occurs in HIV with CD4 < 200/µL; Cotrimoxazole is key for prophylaxis/treatment.
• Lung abscess: Typically caused by anaerobes or S. aureus; air-fluid level on CXR.
• Bronchiectasis: Permanent bronchial dilation, often post-TB; HRCT is diagnostic_tool_code