Epidemiologic association of Chlamydia pneumoniae and atherosclerosis: the initial serologic observation and more.

About 70% of persons with acute myocardial infarction (AMI) show a seroresponse to a chlamydial lipopolysaccharide (LPS) epitope. Elevated titers against Chlamydia pneumoniae in sera from such patients point to an exacerbation in a chronic infection as does a change in the nature of immune complexes containing chlamydial LPS. The presence of antibodies to C. pneumoniae proteins in immune complexes suggests an intimate association of the pathogen with the vascular system. In the first prospective study, elevated antibody titers or immune complexes containing chlamydial LPS were an independent significant risk factor (odds ratio, </=2.6) for AMI 3-6 months before the cardiac incident. The majority of later seroepidemiologic studies have verified the association. However, since serologic markers for C. pneumoniae infection also seem to be associated with uncomplicated atherosclerosis and other chronic conditions, their predictive value for cardiac events is small.