Pneumonia, Mycoplasma



  • Bronchopulmonary infection caused by one of several Mycoplasma spp.; Mycoplasma pneumoniae being the most common pathogen of the class
  • Smallest, free-living organism; fastidious and slow-growing; first isolated in cattle in 1898
  • Most frequently affects children/young adults but can also occur in the elderly; often causes epidemics in close communities (i.e., skilled nursing facilities, dormitories, military barracks)
  • Infection may be asymptomatic, most often confined to the upper respiratory tract; however, may progress to pneumonia (5–10%) (1)
  • Course is usually acute with an incubation period of 1 to 4 weeks.
  • Synonym(s): primary atypical pneumonia (PAP); Eaton agent pneumonia; cold agglutinin–positive pneumonia; walking pneumonia

Pediatric Considerations

  • Increased incidence of asthma exacerbation in older children
  • Infants 3 to 6 months old with suspected bacterial pneumonia should be hospitalized.



  • ~1 million cases/year in United States; annual infection rate of 1% in United States
  • 20% of CAP requiring hospitalizations annually
  • Most frequently in autumn/winter seasons


  • Predominant sex: male = female
  • Predominant age group affected: 5 to 20 years
    • May occur at any age
    • Rare in children <5 years of age
  • Responsible for up to 15–20% of all cases of CAP yearly
    • Most common cause of pneumonia in school children and young adults who do not have a chronic underlying condition

Etiology and Pathophysiology

  • M. pneumoniae is a short-rod mucosal pathogen, which lacks a cell wall and thus not visible on Gram stain.
  • Can grow under both aerobic and anaerobic conditions
  • Highly contagious, transmitted by aerosol droplets
  • Pathogenicity linked to its filamentous tips, which adhere selectively to respiratory epithelial cell membrane proteins with production of H2O2 and superoxide radicals, damaging cilia
  • Decreased ciliary movement produces prolonged paroxysmal, hacking cough.
  • Incubation period is 2 to 3 weeks.
  • M. pneumoniae infection may worsen asthma symptoms as well as cause wheezing in children without asthma.
  • M. pneumoniae infection may worsen chronic obstructive pulmonary disease (COPD) or other chronic pulmonary condition symptoms in adults.

Risk Factors

  • Immunocompromised state (e.g., HIV, transplant recipients, chemotherapy)
  • Smoking
  • Close communal living (e.g., military barracks, prisons, hospitals, dormitories, schools, household contacts, skilled nursing facilities)

Commonly Associated Conditions

  • Asthma exacerbations as a result of proinflammatory cytokine release
  • COPD

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