The incidence of Mycoplasma pneumoniae pneumonia.

BACKGROUND Mycoplasma pneumoniae has been considered a pathogen for humans since the 1940s. Of the 12 species of Mycoplasma found in humans, M pneumoniae is the most widely recognized pathogen. Morbidity from M pneumoniae results from the combined direct effect of cytotoxins produced by the organisms and the indirect effect of inflammatory responses to the presence of the organisms. Several studies have reviewed the incidence of M pneumoniae pneumonia in selected populations with variable results. By using tests that were not definitive detectors of the organism, earlier studies cited have overestimated the true incidence of this infection. We reevaluate several of these early studies in the light of newer findings. METHODS Using the key words "Mycoplasma pneumoniae," "pneumonia," "prevalence," "incidence," and "community acquired," the MEDLINE files from 1992 to the present were searched. Articles dating before 1992 were accessed from cross-reference of the more recent articles. Only clinical trials with a sample size greater than 125 were considered. RESULTS AND CONCLUSIONS M pneumoniae pneumonia occurs in 4- to 5-year cycles and in densely populated areas. Clinical symptoms of M pneumoniae pneumonia include dry cough, sore throat, middle ear involvement, and low-grade fever, as well as additional extrapulmonary manifestations. Bullous myringitis is not a common finding in M pneumoniae infection. Diagnostic tests include cold agglutinins, complement fixation, culture, and enzyme immunoassay. A fourfold rise in M pneumoniae-specific antibody in serum from acutely ill and convalescent patients remains the reference standard for diagnosing the infection. The incidence of M pneumoniae is probably lower than reported in many studies. Using tests that are not diagnostic of the infection can give a falsely elevated incidence of M pneumoniae infection in specific populations.