Community-acquired pneumonia



  • Streptococcus pneumoniae (most common)
  • Haemophilus influenzae
  • Mycoplasma pneumoniae (young adults, summer & fall)
  • Chlamydia pneumoniae (young adults)
  • Staphylococcus aureus (influenza epidemics, IV drug use, bronchiectasis)
  • Neisseria meningitides
  • Moraxella catarrhalis (lung disease, elderly)
  • Klebsiella pneumoniae (alcohol, diabetes)
  • Legionella spp. (contaminated construction site, water source, or air conditioner)


  • Influenza virus
  • Respiratory syncytial virus
  • Adenovirus
  • Parainfluenza virus

Special risk factors

  • Chlamydia psittaci (psittacosis): birds
  • Coxiella burnetii (Q fever): cattle, sheep, goats; especially newborns or products of conception
  • Francisella tularensis (tularemia): tick or skinning rabbit
  • Endemic fungi (Blastomyces: Ohio & Mississippi River valleys; Coccidioides: Southwest United States or Latin America; Histoplasma: Ohio & Mississippi River valleys)
  • Sin nombre virus (hantavirus pulmonary syndrome): rodent waste, Southwest United States

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Last updated: January 13, 2015