Description

• Bronchopulmonary infection caused by the Mycoplasma species, Mycoplasma pneumoniae
• 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 closed communities (i.e., skilled nursing facilities)
• Infection may be asymptomatic, most often confined to the upper respiratory tract; however, may progress to pneumonia (5–10%)
• 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

Geriatric Considerations
The highest rate of ICU admissions for community-acquired pneumonia (CAP) secondary to M. pneumoniae occurs in seniors.

Pediatric Considerations

• Plays a significant role in pneumonias in children of all ages (Pneumonia <5 years, however, viral infection is far more common.)
• Increased incidence of asthma exacerbation in older children (1)[A]
• Infants 3 to 6 months with suspected bacterial pneumonia should be hospitalized.

Epidemiology

Incidence

• Estimated 1 million cases per year in the United States
• Responsible for 20% of CAP requiring hospitalizations annually
• Infection occurs most frequently in fall/winter seasons but may develop year round.

Prevalence

• 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, M. pneumoniae is transmitted primarily 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
• Many pathogenic features of infection are believed to be immune mediated, not directly induced.
• Decreased ciliary movement produces prolonged paroxysmal, hacking cough.
• Incubation period is 2 to 3 weeks.

Risk Factors

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

General Prevention

Consider droplet isolation of active cases.

Commonly Associated Conditions

• Asthma exacerbations as a result of proinflammatory cytokine release (1)[A]
• Chronic obstructive pulmonary disease