Smoking increases the risk of coronary artery disease in Chinese with Chlamydia pneumoniae infection.

Background: The infection with Chlamydia pneumoniae (Cp) has been claimed to associate with coronary artery disease (CAD). However, the seroepidemiological study of association between Cp infection and CAD still remains a source of controversy. The aim of the present study is to investigate the possible association of Cp infection with CAD in Chinese mainland population and the potential role of Cp infection combined with the traditional risk factors in CAD.

Methods: 1422 hospitalized patients with angiographically demonstrated CAD and 297 controls were recruited and tested for specific Cp IgG with enzyme-linked immunoassay (ELISA).

Results: The prevalence of Cp IgG seropositivity in patients with CAD was significantly higher than that in controls (31.1% vs. 24.9%, P=0.035). Unadjusted odds ratios (OR) and 95% confidence intervals (CI) for CAD with the presence of seropositivity of IgG to Cp was 1.4 (1.0-1.8). After full adjustment for possible confounders on multiple logistic regression analysis, only a weak association of Cp infection with CAD was found. The adjusted OR (95% CI) for CAD associated with Cp infection was 1.3 (0.95-1.71, P=0.1). To further delineate the potential role of Cp infection in CAD, we divided subjects into seropositive (n=516) and seronegative (n=1203) groups according to their Cp IgG status. Notably, the adjusted OR (95% CI) for CAD associated with smoking was 4.0 (1.8-8.6) in the seropositive group, 0.9 (0.5-1.4) in the seronegative group, indicating that smoking can significantly increase the risk of CAD in subjects with Cp infection.

Conclusions: Cp infection is not strongly associated with CAD in Chinese mainland population; however, smoking increases the risk of CAD in those with Cp infection.