Mycoplasma pneumoniae

Clinical Background

Mycoplasmas, the smallest self-replicating organisms, include M. pneumoniae (pneumonia), M. genitalium and Ureaplasma urealyticum (urethritis). M. pneumoniae is a common cause of community-acquired pneumonia.

Epidemiology

• Prevalence
  • Responsible for 15-20% of all cases of pneumonia, higher rates among school children and people in closed populations (military recruits)
    • Only 2-5% of patients require hospitalization (15-20% hospitalization rates for other causes of pneumonia)
• Transmission – respiratory droplet
  • Most U.S. outbreaks are in late summer to early fall

Organism

• M. pneumoniae
  • Flask-shaped bacteria that lack a true cell wall and have a very small genome – 816 kilobase pairs (kbp)
  • Facultative intracellular parasites
  • Cultivation in vitro is difficult due to fastidious nature and is heavily dependent on externally supplied growth factors (by host organism or in culture medium) because of limited metabolic capacity inherent in their small genome

Clinical Presentation

• Often indistinguishable from other viral and atypical bacterial pathogens
• Initial symptoms – malaise, myalgias, sore throat, headache (retro-orbital), ear pain and fever
• Symptoms in patients who progress to pneumonia may include chills, chest pain, shortness of breath, nausea, vomiting, diarrhea
• Pulmonary
  • Dry, nonproductive cough occurs 3-5 days after onset of initial nonspecific symptoms
  • Later, cough may produce mucopurulent sputum
  • Patients usually seek medical attention on days 5-7, when cough may become paroxysmal and nocturnal
  • Cough may persist several weeks following resolution of constitutional symptoms
  • Pleural effusions more common in severe disease
• Extrapulmonary manifestations of M. pneumoniae infections
  • Syndromes caused by the spread of organism
    • Bullous hemorrhagic otitis
    • Arthritis
    • Acute respiratory distress syndrome (ARDS)
    • Myocarditis
    • Encephalitis/meningitis
    • Sinusitis
  • Immunologically mediated syndromes
    • Skin rashes
    • Erythema nodosum or erythema multiforme
    • Anemia
    • Thrombocytopenia
    • Guillain-Barré syndrome

Diagnosis

Indications for Testing

• Viral pneumonia presentation with persistent cough

Laboratory Testing 

• PCR – rapid test to identify M. pneumoniae
  • Increased sensitivity if sputum is the sample tested
  • Probably most sensitive test to use, especially in adults who may not mount significant IgM levels early in infection
• IgG, IgM by ELISA, EIA, complement fixation (CF) – usually requires acute and convalescent samples
• Culture – inadequate for acute diagnosis
  • Not recommended because bacteria are relatively fastidious and require a long incubation (up to 4 weeks)
• Differential diagnosis includes Legionella pneumophila  and Chlamydophila pneumoniae
  • Consider serology for M. pneumoniae and urinary antigen detection for Legionella

Imaging Studies

• Chest radiograph findings – patchy, unilateral infiltrates or diffuse, bilateral interstitial process

Differential Diagnosis

• Influenza
• Parainfluenza Virus 1, 2, 3
• Legionella pneumophila
• Chlamydophila pneumoniae or psittaci
• Respiratory simplex virus
• Bordetella pertussis
• Adenovirus
• Metapneumovirus

Indications for Laboratory Testing

• Tests generally appear in the order most useful for common clinical situations
• Click on number for test-specific information in the ARUP Laboratory Test Directory

Click the plus sign to expand the table of additional tests.

Test Name and Number	Comments
Mycoplasma pneumoniae Antibody, IgM 0050398 Method: Enzyme-Linked Immunosorbent Assay	Low IgM antibody levels may persist more than 12 months post-infection
Mycoplasma pneumoniae Antibody, IgG 0050397 Method: Enzyme-Linked Immunosorbent Assay
Legionella Species, Culture 0060113 Method: Standard reference procedures for Legionella culture and identification
Legionella Species by PCR 0056105 Method: Polymerase Chain Reaction
Legionella pneumophila Antigen, Urine 0070322 Method: Enzyme-Linked Immunosorbent Assay