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Mycoplasma pneumoniae Infections: Diagnosis Based on Immunofluorescence Titer of IgG and IgM Antibodies

      Mycoplasmas are small bacteria (0.3 to 0.8 μm in diameter and up to 150 μm in length) that are unique because they have no cell wall. Two genera, Mycoplasma and Ureaplasma (associated with genital infections), are of clinical importance to humans. M. pneumoniae is primarily a respiratory tract pathogen that involves the nasopharynx, throat, trachea, bronchi, bronchioles, and alveoli. Symptomatic infections attributable to this organism most commonly occur in children and young adults (ages 2 to 19 years). The organism has also been associated with infections of the cardiovascular, dermatologic, and central nervous systems. Other mycoplasmas may be present, especially in the upper respiratory tract; however, they are considered part of the normal microbial flora of the oral cavity and do not cause symptoms or disease.

      Epidemiologic Factors.

      Infections with M. pneumoniae occur worldwide throughout the year, especially in temperate climates. Epidemics occur at 4- to 6-year intervals in both civilian and military populations.
      • Denny FW
      • Clyde Jr, WA
      • Glezen WP
      Mycoplasma pneumoniae disease: clinical spectrum, pathophysiology, epidemiology, and control.
      • Noah ND
      • Urquhart AM
      Epidemiology of Mycoplasma pneumoniae infection in the British Isles, 1974-9.
      The infection often seems to be a sporadic, endemic illness in families or closed communities because it has a relatively long izncubation period (2 to 15 days), because its prolonged shedding in nasal secretions may result in additional infections during a protracted interval, and because asymptomatic infections are common.

      Diagnosis.

      M. pneumoniae infections may be diagnosed by cultivation of the organism on complex agar medium or by serologic methods. Because of the slow growth of the organism, partly reflecting fastidious nutrient requirements, culture techniques have been expensive, tedious, and somewhat unproductive. In the clinical microbiology laboratory at the Mayo Clinic, the rate of isolation of the organism has ranged from 0 to 43% from throat and sputum specimens in individual years.
      • Dorman SA
      • Wilson DJ
      • Smith TF
      Comparison of growth of Mycoplasma pneumoniae on modified New York City and Hayflick media.
      The time interval between isolates, however, may be several months because of the sporadic occurrence of these infections. Moreover, the last five isolates of M. pneumoniae in our laboratory necessitated more than 20 days of incubation time before a report could be made. Perhaps genetic probes could produce more timely results with acceptable sensitivity and specificity relative to cultivation of the organism.

      Indirect Immunofluorescence Test.

      Titration of antibodies in acute and convalescent phase serum specimens is usually done with use of the complement fixation reaction. Currently, however, cells that contain M. pneumoniae antigenic substrate are commercially available (Zeus Technologies, Inc., Raritan, New Jersey), and these facilitate performance of the indirect immunofluorescence test
      • Carter JB
      • Carter SL
      Acute-phase, indirect fluorescent antibody procedure for diagnosis of Mycoplasma pneumoniae infection.
      and separate measurement of antibodies of IgG and IgM classes. Of 14 paired (acute and convalescent phase) serum specimens, in each pair of which the presence of an M. pneumoniae infection was confirmed by a rising titer of complement fixation, 11 had fourfold or greater increases in titer, as measured by the indirect immunofluorescence test. One of the three paired serum specimens that did not have a diagnostic serologic increase in titer had IgM class antibody present in both acute and convalescent phase serum samples. Importantly, IgM antibodies, indicative of a current infection, were demonstrated in 13 of the 14 patients. In five patients, IgM antibodies were detected in the acute phase serum sample.
      Twenty serum specimens submitted for cytomegalovirus serology were tested for antibodies to M. pneumoniae by the indirect immunofluorescence test. Seventeen of the 20 specimens (85%) had low levels of IgG antibody directed against the organism; of these, 15 had titers of 1:10 or less. None was positive for IgM antibodies to M. pneumoniae. Exposure to this organism is widespread—in one analysis, more than 90% of asymptomatic, apparently well, Mayo Clinic blood donors had IgG antibodies to M. pneumoniae, as detected by the indirect immunofluorescence test (Fig. 1).
      Figure thumbnail gr1
      Fig. 1Prevalence of IgG antibody to Mycoplasma pneumoniae in 100 Mayo Clinic blood donors, as measured by indirect immunofluorescence (ImF) test. In every case, the IgM antibody was undetectable. Thus, in no case was the infection acute or recent.
      The indirect immunofluorescence test for M. pneumoniae is sensitive and specific and can distinguish between current (IgM antibody) and past (IgG antibody) infections. Nonetheless, examination of both acute and convalescent phase (7- to 10-day) serum specimens is urged, because the IgM antibody may not be demonstrable early in some cases and a rising titer confirms the diagnosis of M. pneumoniae infection.

      REFERENCES

        • Denny FW
        • Clyde Jr, WA
        • Glezen WP
        Mycoplasma pneumoniae disease: clinical spectrum, pathophysiology, epidemiology, and control.
        J Infect Dis. 1971; 123: 74-92
        • Noah ND
        • Urquhart AM
        Epidemiology of Mycoplasma pneumoniae infection in the British Isles, 1974-9.
        J Infect. 1980; 2: 191-194
        • Dorman SA
        • Wilson DJ
        • Smith TF
        Comparison of growth of Mycoplasma pneumoniae on modified New York City and Hayflick media.
        Am J Clin Pathol. 1983; 79: 235-237
        • Carter JB
        • Carter SL
        Acute-phase, indirect fluorescent antibody procedure for diagnosis of Mycoplasma pneumoniae infection.
        Ann Clin Lab Sci. 1983; 13: 150-155