Mycoplasma pneumoniae

Indications for Testing

Viral pneumonia presentation with persistent cough

Laboratory Testing

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 ELISA, EIA, complement fixation – usually requires acute and convalescent samples
- Not effective in early diagnosis
Culture – inadequate for acute diagnosis
- Not recommended; bacteria are relatively fastidious and require a long incubation (up to 4 weeks)
Consider concurrent serology for C. pneumoniae, urinary antigen detection for Legionella, viral studies (eg, DFA panel for respiratory viruses)

Imaging Studies

Chest radiography – patchy, unilateral infiltrates or diffuse, bilateral interstitial process

Differential Diagnosis

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 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
  - Heavily dependent 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
- Patients who progress to pneumonia may have additional symptoms, including chills, chest pain, shortness of breath, nausea, vomiting, diarrhea
Pulmonary infection
- Dry, nonproductive cough occurs 3-5 days after onset of initial nonspecific symptoms
  - Cough may produce mucopurulent sputum later in illness
- 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 infections
- Syndromes caused by spread of organism
  - Bullous hemorrhagic otitis
  - Arthritis
  - Acute respiratory distress syndrome
  - Myocarditis
  - Encephalitis/meningitis
  - Sinusitis
- Immunologically mediated syndromes
  - Skin rashes
  - Erythema nodosum or erythema multiforme
  - Anemia
  - Thrombocytopenia
  - Guillain-Barré syndrome