Objective: To assess the impact of cigarette smoking on coronary heart disease (CHD) and to propose a simple and efficient method to estimate its attributable fraction (AF).
Material and methods: A matched case-control study was conducted in the Regional Hospital of Instituto Mexicano del Seguro Social (Mexican Institute of Social Security) in Morelos State, Mexico, from May to June-2000. Cases were 80 prevalent and incident patients with CHD. One-hundred-sixty controls matched by sex and age were randomly selected from the outpatient clinic. The attributable fraction was obtained through summary estimators, variances, and confidence intervals for matched designs with more than one control per case.
Results: The prevalence of cigarette smoking previous to the coronary event was 80%, compared to 62.1% in controls. Mantel-Haenszel odds ratios showed a positive association of cigarette smoking with CHD (OR, 6.7; 95% CI, 3.2-13.8). The attributable fraction among the exposed was 85% (95% CI, 74-95) while the population attributable fraction was 56% (95% CI, 45-66). The AF in exposed was 65% for males (95% CI, 53-77) and 31% for females (95% CI 14-47).
Conclusions: The long-term smoking AF on CHD is greater than 85%. Such a high AF should be countered with the implementation of primary prevention measures to encourage smoking cessation and with smoking cessation clinics for active smokers. These are the two most important public health interventions to prevent CHD and a variety of chronic diseases.