Prospective study of Chlamydia pneumoniae IgG and IgA seropositivity and risk of incident ischemic stroke

Background and Purpose: Chlamydia pneumoniae infection or exposure to C. pneumoniae was implicated as a risk factor for ischemic stroke. Our aim was to evaluate prospectively the association between the presence of antibodies to C. pneumoniae (IgG and IgA) and the risk of incident ischemic stroke among patients with pre-existing vascular disease. Methods: Sera were collected from 3,090 coronary heart disease patients enrolled in a secondary prevention trial. We measured baseline antibodies (IgG and IgA) in the sera of patients who developed subsequent ischemic strokes (cases, n = 134) during follow-up (mean 8.2 years), and in 134 age- and gender-matched pairs without subsequent stroke or myocardial infarction. Results: The crude relative odds (95%CI) of incident ischemic strokes in seropositive patients at baseline (>1.1 relative value units) were 1.29 (95%CI, 0.69-2.47) for IgG and 1.31 (95% CI, 0.69-2.55) for IgA by matched-pair analyses, and 1.42 (95%CI, 0.69-2.98) for IgG and 1.57 (95%CI, 0.76-3.35) for IgA after adjustments for conventional risk factors and the inflammatory marker, soluble intercellular adhesion molecule-1. We explored the possibility that the risk of ischemic stroke may increase in parallel to increasing antibody titers, but did not demonstrate any significant association. Conclusions: Serological evidence for prior infection with C. pneumoniae did not emerge as an independent risk factor for incident ischemic stroke among patients at high risk due to pre-existing vascular disease.