Description

• Bronchopulmonary infection caused by infection of the lungs and bronchi with Mycoplasma pneumoniae, a fastidious and slow-growing organism
• Infection may be asymptomatic, confined to the upper respiratory tract, or it can progress to pneumonia. Usual course is acute. Incubation period is 1–4 weeks and it includes prodromal symptoms.
• Peaks late summer/fall; most frequent in children/young adults, but also elderly; may cause epidemics (schools, barracks)
• Synonym(s): Primary atypical pneumonia (PAP); Eaton agent pneumonia; Cold agglutinin-positive pneumonia; Walking pneumonia

Geriatric Considerations
Somewhat unusual as an isolated agent in elderly patients

• Unusual in infants and children <5 years; most pneumonia in this age group is viral.
• M. pneumoniae is associated with increased incidence of asthma exacerbation in older children.
• All infants 3–6 months with suspected bacterial pneumonia should be hospitalized (1).

Epidemiology

• Estimated 2 million cases/year in the US. Responsible for 20% of community-acquired pneumonia (CAP) requiring hospitalizations annually in the US
• Incidence does not vary greatly by season, but accounts for higher proportion of pneumonia in the summer (up to 50%).

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

Risk Factors

• Close community living (e.g., hospitals, prisons, military bases, fraternity houses, household contacts)
• Immunocompromised state
• Smoking

General Prevention

• Highly contagious, M. pneumoniae is transmitted by contact and aerosol.
• Consider the isolation of active cases in closed communities (e.g., schools, camps, military bases) and hospitals.
• Azithromycin prophylaxis (standard 5-day course) may lower the attack rate, but is not routinely recommended.

Pathophysiology

• M. pneumoniae is a mucosal pathogen, an exclusively human parasite
• Prolonged paroxysmal, hacking cough seen in this disease is thought to be due to the inhibition of ciliary movement. The organism has a remarkable gliding motility and specialized filamentous tip ends (adhesin proteins) that allow it to burrow between cilia within the respiratory epithelium, eventually causing sloughing of the respiratory epithelial cells.
• H₂O₂ is an important virulence factor, causing oxidative damage to host cells and the loss of cilia.
• Pathogenicity of M. pneumoniae is linked to the activation of inflammatory mediators, including cytokines.

ALERT
Macrolide-resistant M. pneumoniae has emerged in adult CAP and pediatric pneumonia.

Etiology

Infection by M. pneumoniae has come to be recognized as a worldwide cause of CAP (1)

Commonly Associated Conditions

• Asthma: May be exacerbated by associated release of proinflammatory cytokines
• Chronic obstructive pulmonary disease