Objective: To determine whether there is an independent association between infection with Chlamydia pneumoniae and ischaemic heart disease.
Design: Prospective study using a nested case-control design.
Setting: Medical centre in London run by BUPA, a private medical organisation.
Participants: 21 520 professional men aged 35-64 who attended for a medical examination in London between 1975 and 1982.
Main outcome measure: Death from ischaemic heart disease.
Results: The distributions of concentrations of IgG and IgA antibodies to C pneumoniae were similar in the 647 men who subsequently died of ischaemic heart disease and in 1294 age matched controls who did not. There was no material association with heart disease irrespective of the cut-off point chosen to define seropositivity. At a cut-off point that defines 15% of controls as positive, for example, the odds ratios were 1.26 (95% confidence interval 0.95 to 1.68) for IgG and 1.09 (0.82 to 1.43) for IgA.
Conclusions: No material association was found between infection with C pneumoniae and ischaemic heart disease. The size and prospective design of the study and the socioeconomic homogeneity of the cohort minimise both random and systematic error.