Pediatric Mycoplasma Infections Workup

Updated: Jul 23, 2015
  • Author: Archana Chatterjee, MD, PhD; Chief Editor: Russell W Steele, MD  more...
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Workup

Laboratory Studies

Diagnostic tests for M. pneumoniae are most useful in hospitalized children who may be at risk for fulminant pulmonary disease and complications of extrapulmonary illness. Otherwise, clinical and epidemiologic data can guide the care of the ambulatory patient.

  • Tests for M. pneumoniae [60]
    • Bacterial culture is of little practical value because of fastidious growth requirements and slow growth.
    • Serologic diagnosis has been the mainstay of laboratory testing.
      • The cold agglutinin test may be performed at the bedside or in the laboratory. Serum from spun patient blood is combined with type O erythrocytes and incubated at 4°C for several minutes. The degree of agglutination is noted at this temperature and again after rewarming to 37°C to confirm resolution of the agglutination. The serum is diluted serially, and the test is repeated. The highest dilution resulting in agglutination at 4°C is reported as the cold agglutinin titer. The sensitivity of this test is 50-90%, and the specificity is approximately 75%. [1, 10]
      • Paired acute and convalescent sera are best for complement-fixation serology. A positive result requires a more than 4-fold rise in titer between acute and convalescent sera and more than 1:32 titer in a single serum specimen (86-90% sensitive and 87-94% specific). The test is not helpful in guiding diagnostic and therapeutic decisions because elevations in antibody titer may take as long as 3-4 weeks after the onset of disease. Additionally, the antibody response can be diminished or absent in immunosuppressed hosts and infants. [1, 10]
      • Enzyme-linked immunoassay is used to detect immunoglobulin M (IgM) and immunoglobulin G (IgG) directed against M. pneumoniae. Specificity is greater than 99%, and sensitivity is 98% when both findings are obtained. The IgM result may be negative early (at 7-10 d) and may not be helpful in guiding initial therapy. [61]
    • Direct antigen detection in sputum specimens is performed using antigen-capture indirect enzyme immunoassay. Relatively high specificity and sensitivity (91%) are achieved.
    • Detection of nucleotide sequences with a commercially available kit is based on radioiodine-labeled DNA complementary to M. pneumoniae ribosomal RNA. Sensitivity and specificity were 89% in 1 study.
    • Seminested polymerase chain reaction (PCR) assay using 16S ribosomal DNA (rDNA) as a target and real-time PCR assays targeting the gene for P1 adhesion protein are available. [62, 63, 64] They do not rely on an immunologic response; therefore, relatively early detection is possible. Both techniques have high sensitivity and high specificity. Real-time PCR assays have the advantage of speed and the ability to analyze numerous samples.
  • Tests for genital mycoplasmal organisms
    • These organisms are usually detected by means of cultures in special media (beef-heart infusion broth with fresh yeast extract and horse serum), followed by subcultures on agar media. Ureaplasma species usually grow within 1-2 days, and M. hominis grows within 1 week, but Mycoplasma genitalium may require 1-2 months to grow.
    • Antibody studies, organ cultures, and animal inoculation have all been used, but they have little practical application in routine diagnostic laboratories. PCR techniques using clinical specimens from the upper genital tract obtained during laparoscopy may be of value in the future.
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Imaging Studies

Chest radiographs demonstrate characteristic features of M. pneumoniae infection: bilateral pulmonary involvement, multifocal or diffuse disease, and reticular infiltrates. [41] In rare cases, pleural effusions may be superimposed on parenchymal disease; however, one study reported a 23% incidence rate. [41] Late in the course, pleural effusions may be the only remaining feature. Hilar lymphadenopathy can be present in 7-22% of pediatric patients.

High-resolution CT may reveal the lobular distribution, centrilobular involvement, and interstitial abnormalities in M pneumoniae pneumonia better than chest radiography. [13] However, high-resolution CT is more expensive, and radiation exposure is increased. High-resolution CT is usually not indicated in the routine workup of all patients.

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Procedures

Because most infections tend to be mild, few diagnostic procedures need to be performed. In severe lower respiratory infection caused by M. pneumoniae, bronchoalveolar lavage with appropriate testing of the lavage fluid may be needed; antigen detection, PCR, and culturing are used. [60, 61, 62, 63, 64] In the presence of neurological disease of unknown etiology, investigating Mycoplasma serologically and using cerebrospinal fluid (CSF) analysis is prudent. [52]

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Histologic Findings

The histopathology of M. pneumoniae infection is limited to the ciliated respiratory epithelium extending from the trachea to the respiratory bronchiole. The airways are surrounded by mononuclear cell infiltrates. Intraluminal infiltrates may include polymorphonuclear cells and mononuclear cells. [3]

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