Mycoplasma pneumoniae Infection

Diagnosis

Indications for Testing

• Mild illness consisting of upper or lower respiratory illness with gradual onset of
  • Malaise
  • Fever
  • Headache
  • Sore throat
  • Persistent cough
  • Atypical pneumonia appearance on chest x-ray (patchy unilateral or diffuse bilateral infiltrates)
• Appearance of extrapulmonary symptoms in addition to severe pneumonia – usually prompts testing
  • Rash, including Stevens-Johnson syndrome
  • Hemolysis, secondary to IgM cold agglutinins
  • Cardiac involvement including conduction disturbances, arrhythmias, congestive heart failure, and chest pain
  • Central nervous system (CNS) involvement
  • Gastrointestinal manifestations, eg, nausea, vomiting, and diarrhea
  • Joint pain
• If indications are not present, testing for Mycoplasma pneumoniae is not indicated as this is usually a mild, self-limited disease that responds to macrolide antibiotics

Laboratory Testing

• Polymerase chain reaction (PCR) 
  • Rapid test to identify M. pneumoniae
  • Increased sensitivity if sputum is tested and infection is in early stage (first 21 days after onset)
  • Probably most sensitive test to use, especially in adults who may not mount significant IgM levels early in infection
• IgG, IgM by enzyme-linked immunosorbent assay (ELISA), complement fixation
  • Usually requires acute and convalescent samples
  • Not effective in early diagnosis
• Cold agglutinins – especially if hemolysis is present or suspected
  • Negative result does not rule out infection
    • 30-50% of patients with M. pneumoniae will develop cold agglutinins (Fischbach, 2009)
• Culture
  • Inadequate for acute diagnosis
  • Not recommended; bacteria are relatively fastidious and require a long incubation (up to 4 weeks)
• Consider concurrent testing for Chlamydia pneumoniae, urinary antigen detection for Legionella, viral studies (eg, PCR panel) for respiratory viruses

Imaging Studies

Chest radiography – patchy unilateral infiltrates or diffuse bilateral interstitial process

Differential Diagnosis

• Influenza
• Parainfluenza virus 1, 2, 3
• Legionella pneumophila
• C. pneumoniae or psittaci
• Respiratory syncytial virus
• Bordetella pertussis
• Adenovirus
• Metapneumovirus
• Hantavirus

Background

Epidemiology

• Prevalence
  • Responsible for 15-20% of all community-acquired pneumonia; higher rates among school children and people in closed populations (military recruits)
  • 2-5% of patients require hospitalization as compared with 15-20% hospitalization rates for other causes of pneumonia
• Transmission
  • Respiratory droplet
  • Most common in U.S. during late summer to early fall

Organism

• M. pneumoniae
  • Flask-shaped bacteria with no true cell wall and a very small genome (816 kilobase pairs)
  • Facultative intracellular parasite
  • Cultivation in vitro is difficult
    • Fastidious nature
    • Dependence on externally supplied growth factors (by host organism or in culture medium)
    • Limited metabolic capacity inherent in small genome

Clinical Presentation

• Most infections are mild and often indistinguishable from other viral and atypical bacterial pathogens
• Initial symptoms
  • Malaise, myalgias, sore throat, headache (retro-orbital), ear pain, and fever
• Advanced infection
  • Dry, nonproductive cough occurs 3-5 days after onset of initial nonspecific symptoms
  • Cough may produce mucopurulent sputum later in illness
  • May be accompanied by chills, chest pain, shortness of breath, nausea, vomiting, diarrhea
  • Patients usually seek medical attention after 5-7 days – 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 infection
  • Syndromes caused by spread of organism
    • Bullous hemorrhagic otitis
    • Arthritis
    • Acute respiratory distress syndrome
    • Myocarditis with conduction disturbances and chest pain
    • Encephalitis/meningitis
    • Sinusitis
  • Immunologically mediated syndromes
    • Hemolysis/hemolytic anemia
    • Skin rashes
    • Erythema nodosum or erythema multiforme
    • Thrombocytopenia
    • Guillain-Barré syndrome