Detection of IgM antibodies to Chlamydia trachomatis, Chlamydia pneumoniae, and Chlamydia psittaci from Japanese infants and children with pneumonia.

Chlamydia trachomatis (C. trachomatis) is now well established as a pathogen of neonatal inclusion conjunctivitis and infantile pneumonia. C. pneumoniae (TWAR) and C. psittaci also cause pneumonia and other respiratory infections. Serum samples from 223 Japanese infants and children with pneumonia were tested for IgM antibodies to C. trachomatis, C. pneumoniae and C. psittaci. IgM antibodies to C. trachomatis were measured by an enzyme immunoassay (EIA) and by a microimmunofluorescence (MIF) test. IgM antibodies to C. pneumoniae and C. psittaci were determined by MIF. Of 223 patients, 48 (21.5%) were positive for IgM antibodies to C. trachomatis, 11 (4.9%) were positive for C. pneumoniae and 5 (2.2%) were positive for C. psittaci. From nasopharyngeal swabs collected from 87 infants with pneumonia (0 to 1 year of age), we attempted to isolate C. trachomatis with tissue culture. C. trachomatis was isolated from 23 (26.4%) of 87 infants with pneumonia, and IgM antibodies to C. trachomatis were detected in 17 (19.5%) of them. Our data suggest a role for chlamydial infection in childhood pneumonia beyond infancy with both C. trachomatis and C. pneumoniae being contributing pathogens.