Risk factors

These include:

• smoking
  
  
• alcohol
  
  
• preceding viral infections:
  • for example influenza predisposing to Streptococcus pneumoniae infection
    
    
• bronchial obstruction:
  • chronic obstructive airways disease
  • bronchial carcinoma
    
    
• bronchiectasis e.g. cystic fibrosis
  
  
• immunosuppression:
  • AIDS
  • cytotoxic therapy
  • usually involving PCP, CMV or Mycobacterium avium
    
    
• intravenous drug abuse, often with Staphylococcus aureus infection
  
  
• inhalation from oesophageal obstruction, often associated with anaerobes
  
  
• hospitalisation - often involving gram-ve organisms
  
  
• underlying predisposing disease:
  • diabetes mellitus
  • cardiovascular disease