[Serologic diagnosis of Mycoplasma pneumoniae infections].

Mycoplasma pneumoniae is a human pathogen with worldwide distribution. This microorganism is a common cause (10-30%) of community-acquired pneumonia, also called primary atypical pneumonia because of the spectrum of clinical and radiological findings. The immune response is mainly based on rapid antibody production against peptide and glycolipid antigens derived from this microorganism. During the primary infection, IgM levels generally rise within the first week, and are then followed by an IgG response. Titers of IgG and IgA increase in reinfections. Microbiological diagnosis is based on specific antibody detection. Polymerase chain reaction (PCR) techniques performed on sputum or pharyngeal/nasopharyngeal exudates, as well as the development of multiplex PCR reactions allowing identification of M. pneumoniae and other respiratory pathogens, would by highly useful in routine diagnosis. The most common serological techniques are complement fixation, immunofluorescence, particle agglutination, and enzyme immunoassay. Diagnosis should be performed by selecting the most appropriate test according to functional criteria and population groups. Specific detection of IgM antibodies should not be included in the differential diagnosis in adults and young people. Diagnostic criteria including seroconversion or rising IgG titers may not be clinically useful, because of the time delay and the difficulty of obtaining a second serum specimen for testing, given the mildness of the clinical symptoms.