Pneumonia

• Acute lower respiratory tract infection associated with changes visible on CXR
• Classification
  • Community acquired = up to 48 hours since admission, common pathogens: S. pneumoniae, H. influenza, M. catarrhalis, Atypicals (M. pneumonia, S. aureus, Legionella, Chlamydia)
  • Hospital-acquired pneumonia = 48 hours or more after admission. Common pathogens: Gram negative enterobacteria, S. aureus, P. aeruginosa, Klebsiella, Bacteroides, Clostridia
  • Aspiration pneumonia: associated with stroke, bulbar palsy, poor dental hygiene. Common pathogens: anaerobes
  • Immunocompromised host: Pneumocystis jirovecii, mycobacteria, fungi, viruses

Signs and symptoms

• Fever, rigors, tachypnoea, tachycardia
• Purulent sputum, haemoptysis
• Pleuritic chest pain

Investigation

• Blood tests (CBC, CRP, LFT, U+E’s, haemoculture)
  
  

  CURB-65 Scoring System

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  • C: Confusion (1)
  • U: BUN ≥ 19 mg/dL (1)
  • R: Respiratory Rate ≥ 30/min (1)
  • B: Systolic BP ≤ 90 mmHg or Diastolic BP ≤ 60 (1)
  • 65: Age ≥ 65 (1)
  
  
• Chest X-ray
• Chest ultrasound (for pleural effusion, empyema)
• Urine antigen (if suspecting Pneumococcal spp (CURB ≥ 2) or Legionella spp. (CURB ≥ 3))
• Bronchoalveolar lavage (chronic infection, ?TB, immunocompromise)

Management

• Community-acquired pneumonia (empirical)
  • CURB = 0-1 → amoxicillin 500mg -1 g tid PO or clarithromycin 500 mg bid or doxycycline 200 mg loading + 100 mg od for 5 days
  • CURB = 2 → amoxicillin + clarithromycin or doxycycline (same dosage as above). Alternatively IV amoxicillin 500 mg tid + clarithromycin 500 mg bid for 7 days
  • CURB = 3 or more → IV co-amoxiclav 1.2 g tid OR IV cephalosporin + clarithromycin 500 mg bid for 7 days
  • If Staphylococcal → flucloxacillin + rifampicin. Vancomycin if MRSA suspected.
  • Atypical: Legionella → clarithromycin + fluoroquinolone, Chlamydia → tetracycline, Pneumocystis → co-trimoxazole
• Hospital-acquired pneumonia
  • IV aminoglycoside + IV piperacillin-tazobactam or IV cephalosporin (3rd gen)
• Aspiration pneumonia
  • IV cephalosporin + IV metronidazole
• Neutropaenic patient
  • Same as hospital-acquired, may add antifungals if no improvement after 48 hours

Note:

• Streptococcus pneumoniae: most common, more common among hyposplenic/asplenic, pre-existing lung disease or immunocompromised patients
• Staphylococcus: common after influenza, in CF patients, may cause bilateral cavitating bronchopneumonia
• Klebsiella: more common among diabetics, alcoholics, elderly, can cause upper lobe cavitating bronchopneumonia
• Pseudomonas: more common among CF, bronchiectasis and hospital-acquired pneumonia patients
• Mycoplasma: causes reticular nodular or patchy consolidation → worse CXR than clinical status, associated with cold agglutination autoimmune haemolytic anaemia
• Legionella: colonized water tanks/AC, associated with lymphopaenia, hyponatraemia, deranged LFT
• Pneumocystis: more common among immunocompromised patients, bilateral perihilar interstitial shadowing
• Chlamydophila psittaci: from birds, may cause arthralgia, endocarditis, meningoencephalitis

Complications of pneumonia

• Respiratory failure
• Septic shock
• Pleural effusion, empyema or lung abscess
• Atrial fibrillation

Reference: Oxford Handbook of Clinical Medicine (10th Ed)