Abstract
Background Population-based studies of the association between smoking and Chlamydia pneumoniae seropositivity do not exist. The role of smoking in the association between C. pneumoniae seropositivity and coronary artery disease (CAD) suggested by several studies has been debated. The aim of this study was to determine the relationship between smoking habits and C. pneumoniae IgG antibody tltres in a middle-aged population. We also wanted to find out whether the difference in smoking habits between the sexes explains the higher C. pneumoniae antibody prevalence among men compared with women. Results After controlling for the effect of smoking, the risk of C. pneumoniae seropositivity remained 1.4 times higher in men than in women. In men, the estimated risk for C. pneumoniae seropositivity (titre ≥1:16) was significant only for smokers (adjusted odds ratio [OR] = 1.4). The adjusted OR for high seropositivity (titre ≥1:128) was 1.5 for smokers and 1.7 for ex-smokers. The risk for women was similar to that for men. Conclusions The results provide evidence of an association between smoking and C. pneumoniae seropositivity in the general population. The higher prevalence of smoking in men does not explain the C. pneumoniae antibody prevalence in men compared with women.