Smoking is a potential confounder of the Chlamydia pneumoniae-coronary artery disease association.

Abstract

Two recent studies, which did not adequately control for smoking status, found associations between Chlamydia pneumoniae serological titers and various manifestations of coronary artery disease (CAD). The validity of C. pneumoniae-CAD associations found in case-control studies has been criticized on the basis that smoking, known to be associated with CAD and hypothesized to be associated with C. pneumoniae seroreactivity via an increased prevalence of respiratory infection in smokers, could be an uncontrolled confounder in these studies. We investigated associations between current smoking status and C. pneumoniae serological titers in a cohort of 365 outpatients (mean age, 34 years) with respiratory illness. Current smokers were significantly (p=0.04) more likely than nonsmokers to have C. pneumoniae titers 2:1:128, and there was a significant (p<0.05) "dose-response" association between titer category and smoking, which persisted after controlling for age and sex in a logistic-regression model. These results support the hypothesis that smoking may be a confounder of the association of C. pneumoniae antibody titer and smoking-associated diseases such as CAD. Future studies into these associations should control for cigarette use.

Chlamydia pneumoniae Antibodies in Severe Essential Hypertension

“…[23][24][25] In this study, we found no noteworthy interactions (ie, effect modification) by these factors with the association between C. pneumoniae and hypertension. Subjects in the HT and control groups also differed in some other demographic characteristics whose influences on the risk of C. pneumoniae infection were unknown (Table).…”

Association ofChlamydia pneumoniaeIgA antibodies with recently symptomatic asthma

“…Current [19,20] and exsmokers [20] have more seropositivity and higher titres of C. pneumoniae antibodies than non-smokers. It has been suggested that the associations between smoking and chronic cardiopulmonary disease may be mediated by the promotion of C. pneumoniae infection [19]. This small study was not designed to address pathogenic pathways involving smoking, infection and asthma, nor was it powerful enough to detect potentially significant interactions of smoking and infection.…”

Multiple Infections and Subsequent Cardiovascular Events in the Heart Outcomes Prevention Evaluation (HOPE) Study

“…We found that chlamydial antibodies were significantly more common among men and smokers, validating associations noted by others. 23,24 We specifically sought an interaction between C pneumoniae, smoking, and CV events, hypothesizing synergy between smoking and infection. Although the interaction term was statistically significant, the relation between C pneumoniae IgA and CV events persisted only in former smokers or never-smokers.…”

“…Thus, smoking may be a confounding factor in the C pneumoniae-heart disease association, as originally suggested by Hahn and Golubjatnikov. 23 Alternatively, smoking and chlamydial infection may be part of the same causal pathway, such that no excess risk is associated with chlamydial infection after controlling for smoking.…”