Relation of Chlamydia pneumoniae serology to mortality and incidence of ischaemic heart disease over years in the Caerphilly prospective heart disease study

Objectives To investigate the effect of Chlamydia pneumoniae infection on f uture development of ischaemic heart disease and mortality Design Prospective longitudinal study. Setting Caerphilly South Wales. Subjects Plasma specimens were collected during 1979-83 from 1773 men aged 45-59 years. These were tested for IgG and IgA antibodies to C pneumoniae ( TW183) by microimmunonfluorescence. Outcome measures 13 year mortality and incident ischaemic heart disease eve nts were ascertained from death certificates, hospital records, and electro cardiographic changes at follow up every 4 to 5 years. Results 642 men (36.2%) had Ige antibodies at a titre of greater than or eq ual to 1 in 16, of whom 362 (20.4% of all men) also had detectable IgA anti bodies. The prevalence of ischaemic heart disease (a history of past or cur rent disease) at entry was similar at all IgG antibody titres but was posit ively related to IgA antibody titre. IgA antibody titre was positively corr elated with plasma viscosity but not with other cardiovascular risk factors . Incidence of ischaemic heart disease was not associated with either IgG a ntibody titre or IgA antibody titre, but there were stronger and significan t relations of IgA antibodies with all cause mortality and fatal ischaemic heart disease, which persisted after adjustment for conventional cardiovasc ular risk factors. The odds ratios associated with detectable IgA antibodie s were 1.07 (95% confidence interval 0.75 to 1.53) for all incident ischaem ic heart disease, 1.83 (1.17 to 2.85) for fatal ischaemic heart disease, an d 1.50 (1.10 to 2.04) for all cause mortality. Conclusion This is the first prospective demonstration of an association be tween IgA antibodies to C pneumoniae, a putative marker of chronic infectio n, and subsequent risk of death from ischaemic heart disease. In contrast t o earlier case-control studies, Ige antibodies were not associated with eit her prevalent or incident ischaemic heart disease.