Abstract

Although Chlamydia pneumoniae is a well-described and common respiratory tract pathogen, up to 90% of infections with this organism are thought to be asymptomatic. Because asymptomatic infection with C. pneumoniae has not been studied in a systematic manner, we conducted a prospective study of healthy adults to establish the prevalence of asymptomatic infection. Nasopharyngeal swab specimens were obtained from 104 subjectively healthy people and evaluated by culture and polymerase chain reaction-enzyme immunoassay (PCR-EIA) for the presence of the organism. Serum obtained from 103 of these individuals was tested by microimmunofluorescence for the titer of specific antibody to C. pneumoniae. For two individuals, C. pneumoniae was identified in nasopharyngeal specimens by culture and/or PCR-EIA; one of these individuals had an IgG titer of 1:256, whereas the other had no detectable antibody. Of the remaining 101 individuals with negative culture and PCR-EIA results, 19 fulfilled presently accepted serological criteria for acute infection; i.e., the IgM titer was > or = 1:16, the IgG titer was > or = 1:512, or both. On the basis of our findings, we conclude that asymptomatic upper airway infection and carriage with C. pneumoniae occur among subjectively healthy persons; we also propose that such individuals may represent a reservoir for this organism in the community. Further, this study demonstrates that currently available diagnostic tests for C. pneumoniae may be unable to accurately distinguish between infection responsible for respiratory tract disease and that representing carriage.