Community Acquired Pneumonia – lecture notes

Risk factors for CAP include:

• Age over 50 years
• Asthma
• Smoking and pre-existing COPD
• DM, CRF, CCF, alcoholism, liver disease
• Neoplasia
• Stroke
• Seizures
• Aspiration
• Immunosuppression, institutionalisation, indigenous.

Johnson P, Irving L et al. Community-acquired pneumonia. MJA 2002; 176:341-347 [Reference]

Most common organism

• Strep pneumoniae + most severe illness and deaths.
  
• Also Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella, H.influenzae (usually with COPD)

Pneumonia Severity Index (PSI)

• Can be used to classify patients into risk classes I (30 day-mortality 0.1%) to IV (mortality 9.3%) or V (mortality 27%)
• Based on history/ age/ NH resident /coexisting illness / physical signs / investigations.
• Note may underestimate severity in the young, sick hypoxic patient.

Severe PSI class V would include:

• Respiratory failure:
  • Resp rate ≥ 30/min.
  • PaO2 < 60 mmHg, SaO2 < 90% on room air.
• Haemodynamic compromise:
  • Pulse ≥125/min.
  • SBP < 90 mmHg.
• Other physical features:
  • Confusion.
  • Temp <35 or ≥ 40 degrees.
• Investigation results:
  • Na < 130mmol/L
  • Urea ≥11mmol/L
  • gluc ≥ 14 mmol/L
  • Hct <30%
  • pH <7.35
  • effusion on CXR.

A simpler alternative scoring system is the 5-point CURB-65 score, with one point for each of

• Confusion
• Urea > 7 mmol/l
• Resp rate ≥ 30/min
• Blood pressure low (SBP < 90 mmHg or DBP ≤ 60 mmHg)
• Age ≥ 65 yr.
• Score 4 = 41.5%, and score 5 = 57% mortality or need for ICU. Score 0 or 1 = 0.7% and 3.2% respectively. Thus score 0 or 1 patients could be treated at home, score 2 need hospital assessment and ≥ 3 are considered severe. Score ≥ 4 consider for ICU.

Lim WS et al. Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study. Thorax 2003;58:377-82. [Reference]

Empiric antibiotic treatment after 2 sets of blood cultures if severe (5-10% yield), and sputum if rapidly available (do not delay treatment to collect sputum, as yield ≤ 40% only).

• PSI Class I or II – could go home: amoxycillin plus roxithromycin / clarithromycin or doxycycline, all orally.
• PSI Class III or IV – admit: benzylpenicillin or amoxy/ampicillin IV plus either roxithromycin / clarithromycin, or doxycycline orally plus gentamicin if Gram -ve suspected.
  • If tropical regions with risk factors for Acinetobacter baumannii or melioidosis (Burkholderia pseudomallei) such as diabetes, alcoholism, CRF or chronic lung disease, use ceftriaxone plus gentamicin IV.
• PSI Class V – consider ICU: azithromycin or erythromycin IV plus either Ceftriaxone or cefotaxime IV or Benzylpenicillin plus gentamicin IV.
  • If tropical regions (all patients) meropenem or imipenem IV plus either azithromycin or erythromycin IV

Therapeutic Guidelines Ltd. Therapeutic Guidelines. Antibiotic; Version 13, 2006:199-209.

In HIV patients, pneumocystis jirocveci (carinii) pneumonia is the commonest AIDS-defining illness and cause of death. Also TB has 100-fold increased relative risk, and can not be excluded on CXR findings alone.

Mandell L, Wunderink R, Anzueto A et al. Infectious Diseases Society of America/ American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis 2007;44:Suppl 2: S27-72. [Reference]

Eddy O. Community-acquired pneumonia: from common pathogens to emerging resistance. Emergency Medicine Practice 2005;7(12):1-24. [EBmedicine.net]

British Thoracic Society Pneumonia Guidelines Committee. 2004 Update. [Reference PDF] {next update due 2009}.

Community-acquired pneumonia. File TM. Lancet 2003; 362:1991-2001. [Reference]