Significant association of cagA positive Helicobacter pylori strains with risk of premature myocardial infarction

Objective-To investigate whether genetic diversity of Helicobacter pylori i nfluences its association with coronary heart disease, and specifically whe ther the risk is confined to infection with the more virulent strains beari ng the cytotoxin associated gene-h (cagA) antigen. Design and setting-Case-control study in hospital admitting unselected pati ents with myocardial infarction. Methods and subjects-Serological status for cagA and H pylori were determin ed in 342 cases of acute myocardial infarction and 214 population based con trol subjects free of clinical coronary heart disease. Results-38.0% of cases and 30.8% of controls were cagA seropositive (odds r atio 1.38, 95% confidence interval (CI) 0.94 to 2.01,p = 0.08). In subjects < 65 years old (153 cases, 153 controls), cagA seropositivity was associat ed with a 1.80-fold increase (95% CI 1.07 to 3.03, p = 0.02) in myocardial infarction risk, which increased further to 2.25-fold (95% CI 1.12 to 4.53, p = 0.01) in subjects < 55 years. There was no significant association of cagA status with classical coronary heart disease risk factors. H pylori se ropositivity was present in 60.2% of cases and 53.7% of controls (odds rati o 1.12, 95% CI 0.83 to 1.51, p = 0.43). H pylori seropositivity was not inc reased in young cases and did not show any interaction with age. Conclusions-The association of chronic H pylori infection with risk of myoc ardial infarction appears to be restricted to cagA bearing strains. The ass ociation is age dependent and stronger in younger subjects. Genetic heterog eneity of H pylori may explain some of the discordant findings with regard to the association of H pylori with coronary heart disease.