A) Filamentous Mycoplasma pneumoniae cells B) M. pneumoniae cells (M) attached to ciliated mucosal cells by the attachment organelle (indicated by arrow) https://en.wikipedia.org/wiki/Mycoplasma_pneumoniae
Mycoplasma are the smallest free-living, self-replicating organisms known. These bacteria are contained by a trilayered cell membrane and do not contain a cell wall. They are therefore resistant to beta-lactam antibiotics and do not stain by Gram stain. They are difficult to grow in culture media and their growth is slow.
- Mycoplasma pneumoniae (MP) causes up to 40% of community-acquired pneumonia in children and up to 18% of cases requiring hospitalization. The incidence of MP pneumonia is greatest among school-age children and declines after adolescence.
- MP infection most often causes tracheobronchitis rather than pneumonia. Infection is usually mild and may be asymptomatic in adults with a history of previous infection.
- The incubation period is 1-3 weeks.
- The bacteria are spread by large particles by aerosol to close contacts. The spread is increased within closed settings.
- MP are inhaled by the host and attach to cells in the respiratory tract. The bacteria produce a P1 adhesin protein that allows attachment to a receptor on the respiratory tract epithelial cells.
- Mycoplasma will induce damage to respiratory epithelium from the trachea to bronchioles. Alveoli are usually spared.
- Manifestations of illness are mostly confined to the respiratory system, but some cases are associated with extrapulmonary involvement.
- Cold agglutinins are auto-antibodies believed to be the result of antigenic aleration of erythrocytes induced by MP. They may be detected in about 50% of cases and appear about 2 weeks after infection and may last for 6-8 weeks. The height of the titer may correlate with the seriousness of the illness.
- The symptoms of MP infection develop gradually over a period of several days and can persist for weeks to months.
- MP infections may involve the upper respiratory tract, the lower respiratory tract, or both.
- The symptoms are often similar to those caused by other respiratory pathogens.
- The most common symptoms include fever, cough, malaise, headache, and sore throat. Chest auscultation often reveals rales, rhonchi, and expiratory wheezes.
- Progression to bronchopneumonia is more common in older children (aged 5-15 years) and is relatively rare in younger children (under 5 years).
- Radiographic findings
- Most frequently: interstitial infiltrates with predilection for lower lobes, commonly with hilar adenopathy
- Occasionally presents with a lobar pneumonia
- Pleural effusions are not rare
- The xray classically looks worse than the clinical picture.
- MP infections are frequent triggers of reactive airway disease (asthma). There is recent speculation regarding a possible role of MP in the development of asthma.
- Extrapulmonary symptoms occur in almost 20% of patients with MP infection requiring hospitalization. They are thought to be autoimmune-mediated and include rashes, Stevens-Johnson Syndrome, meningoencephalitis, hemolytic anemia, arthritis, and gastrointestinal symptoms.
- Viral infections- adenoviruses, parainfluennza, influenza
- Chlamydia pneumonia
- Legionnaire's disease
- Bacterial pneumonias
- Diagnostic tests are of limited use. There is no test that allows rapid, reliable diagnosis of MP infection.
- White blood cell count may be normal or slightly elevated.
- Cold agglutinin titers >1/64 are found in adolescents and adults in approximately 50% of cases. This test is not reliable in children < 12 years of age. Difficult test to perform and should be limited to diagnose older patients. Other atypical pneumonias may induce low titers of cold agglutinins.
- CF titers- Difficult to perform and must demonstrate rising and falling titers.
- IgM- must wait until 8-10 days of illness before detected, therefore not clinically helpful in most situations.
- PCR- not readily available
- Presence of polys in sputum without organism is suggestive of Mycoplasma infection.
- Treat with a macrolide (e.g. Azithromycin x5 days). Will also be effective against other community acquired infections such as pneumococcal pneumonia.
- Tetracyclines can be used in patients > 10 years old.
- Fluoroquinolones are not routinely used in patients <18 years.
- May isolate organism for months after treatment.
- Cimolai N. Mycoplasma pneumoniae Respiratory Infection. Pediatrics in Review 1998
- Wubbel L. et al. Etiology and treatment of community-acquired pneumonia in ambulatory children. The Ped. Infectious Dis. Journal 1999
- Kim C.K. et al. Late Abnormal Findings on High-Resolution Computed Tomography after Mycoplasma Pneumonia. Pediatrics. 2000
- Waites K.B. New concepts of Mycoplasma pneumoniae infections in children. Pediatric Pulmonology 2003