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Diagnosis of infections due to Mycoplasma pneumoniae
Mycoplasma pneumoniae is a small bacterium transmitted via organism-containing droplets. It is a cause of upper respiratory infection, pharyngitis, and tracheobronchitis, particularly in children, and has been associated with approximately 20% of cases of community acquired pneumonia.(1) Central nervous system and cardiac manifestations are probably the most frequent extrapulmonary complications of infections due to Mycoplasma pneumoniae. The disease is usually self-limited although severe disease has been reported in immunocompromised patients.(2)
Identification of Mycoplasma pneumoniae by culture-based methods is time consuming and insensitive. Serology based assays for Mycoplasma pneumoniae have several drawbacks. The development of IgM antibodies takes approximately 1 week and the IgM response in adults may be variable or it may be decreased in immunosuppressed individuals.(3,4) Confirmation of the disease may be dependent on the observation of a 4-fold rise in IgG antibody titers between acute and convalescent specimens, several weeks following the initial onset of illness, providing clinical utility only for retrospective testing.(4) Real-time PCR offers a rapid and sensitive option for detection of Mycoplasma pneumoniae DNA from clinical specimens.
A positive result indicates the presence of Mycoplasma pneumoniae.
A negative result does not rule out the presence of Mycoplasma pneumoniae and may be due to the presence of inhibitors within the specimen matrix, or the presence of organisms at numbers below the limits of detection of the assay.
This assay should only be used for testing of respiratory tract specimens (throat swabs, nasopharyngeal swabs, tracheal secretions, sputum, and bronchoalveolar lavage fluid) and pleural/chest fluid, pericardial fluid, and cerebrospinal fluid.
The assay was validated in a blinded manner using 30 Mycoplasma pneumoniae-positive specimens received from a reference lab and 6 negative specimens. The Mycoplasma pneumoniae PCR (Mayo) had 100% sensitivity and specificity when compared to the Focus Diagnostics Mycoplasma pneumoniae primer pair PCR assay. Whole organism spiking studies (near the limit of detection of the assay) were also performed using the following specimens: bronchoalveolar lavage/bronchial wash, nasopharyngeal and throat swabs, sputum, pericardial/pleural fluid, and cerebrospinal fluid. These specimens were confirmed as being negative for Mycoplasma pneumoniae prior to spiking. The sensitivity and specificity of the spiked specimens combined for all the matrices were 99% (154/155) and 100% (57/57), respectively.
Limit of detection:
The limit of detection of the assay is <5 target copies/mcL for all validated specimen types.
The assay was tested against a panel of 45 organisms consisting of bacteria and viruses representing normal respiratory flora and/or respiratory pathogens. There was no cross reactivity among these organisms which included 16 other species of Mycoplasma.
3. Daxboeck F, Krause R, Wenisch C: Laboratory diagnosis of Mycoplasma pneumoniae infection. Clin Microbiol Infect 2003;9:263-273