Lack of evidence of Chlamydia pneumoniae infection in infants with acute lower respiratory tract disease.

In order to determine whether there is serologic evidence of Chlamydia pneumoniae infection in young infants with acute lower respiratory tract infection, serum samples from 86 subjects aged less than 6 months were assayed for IgG and IgM antibodies to Chlamydia pneumoniae using a microimmunofluorescence method. Infants hospitalized in Toronto, Canada, were enrolled between 15 March 1991 and 15 March 1992. No patient had infection determined by the serologic results. IgG antibody was detected at low concentrations in 32 patients, with an inverse relationship between titer and chronological age. In our setting, Chlamydia pneumoniae does not appear to be an important lower respiratory pathogen in young infants.