Mycoplasma pneumoniae

Snapshot

• An 18-year-old college student presents to the student health clinic with a mild fever, headache, fatigue, and a dry, non-productive cough. He says that his symptoms started about 3 weeks ago and have not improved. The physician obtains a chest radiograph, which shows a pattern of diffuse interstitial infiltrates that appears worse than the patient’s physical appearance. The patient is prescribed azithromycin for his infection.

Introduction

• Classification
  • Mycoplasma pneumoniae
    • pleomorphic
    • no cell wall
    • cell membrane contains cholesterol
    • causes an atypical “walking” pneumonia 
• Epidemiology
  • demographics
    • more common in patients < 30 years of age
  • risk factors
    • frequently seen among young individuals living in close contact
      • college students living in dormitories
      • military recruits
      • prisoners
• Pathogenesis
  • transmission
    • respiratory droplets
  • Mycoplasma pneumoniae attaches to the respiratory epithelium, destroys the superficial layer of respiratory epithelial cells, and reduces the ability of the upper airways to clear themselves
• Associated conditions
  • cold autoimmune hemolytic anemia 
  • erythema multiforme
  • acute interstitial nephritis
• bacterial myocarditis

Presentation

• Symptoms 
  • mild fever 
  • headache
  • non-productive cough
• Physical exam
  • non-productive cough
  • bilateral wheezing may be heard on auscultation
• macropapular or vesicular rash

Imaging

• Chest radiography
  • patchy or diffuse interstitial infiltrates
• chest radiograph often looks more severe than the patient’s actual presentation

Studies

• Labs
  • detection of high titer of cold agglutinins (IgM antibodies) on serology 
    • cold agglutinin production peaks during the third week of infection
• Microbiological studies
  • growth on Eaton agar
  • not seen on Gram stain due to lack of a cell wall
• Making the diagnosis
• based on clinical presentation and laboratory studies

Differential

• Viral infection
  • distinguishing factor
    • would not produce high titer of cold agglutinins (IgM)
• Chlamydophila pneumoniae infection
  • distinguishing factor
    • d3 cytoplasmic inclusions (reticulate bodies) seen on Giemsa or fluorescent antibody-stained smear
• Legionella infection
  • distinguishing factor
    • different demographic
      • more common in smokers and patients with chronic lung disease
• grows on charcoal yeast extract agar buffered with cysteine and iron

Treatment

• Medical
  • macrolide antibiotics (especially Azithromycin)
  • doxycycline
• fluoroquinolones

Complications

• Autoimmune hemoltyic anemia
• Acute interstitial nephritis
• Bacterial myocarditis