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An earlier case-control study from Stockholm, Sweden showed no convincing evidence for an association between occupational exposure to motor exhaust and acute myocardial infarction. We updated the exposure assessments using a Job-exposure matrix (JEM) and analyzed dose-response and influence of time since last exposure.
Methods
Stockholm Heart Epidemiology Program is a case-control study comprising cases of first myocardial infarction and population controls recruited 1992–1994 in Stockholm County. This analysis was based on 1325 nonfatal cases and 1668 controls. A motor exhaust measurement program investigated exposure levels and was used to develop a JEM. Elemental carbon (EC) was used as an indicator for motor exhaust exposure. The JEM was applied to the life-time personal work histories of the study subjects. ORs were estimated adjusting for sex, age, hospital catchment area, life time smoking habits, diabetes and overweight.
Results
25 % of the referents were ever occupationally exposed to EC for at least one year. Subdivision by the highest annual average exposure intensity during the occupational history showed increasing ORs with increasing exposure, OR=1.37 (95% CI 1.06-1.79) for the highest tertile among the exposed (p for trend = 0.02). A similar analysis using cumulative exposure showed slightly lower ORs and a non-significant trend (p=0.25). The OR was higher among those with more recent exposure (within last 20 years, excluding the last two years) OR = 1.28 (0.98-1.67) than among those with last exposure more than 20 years ago OR=0.77 (0.57-1.05)
Discussion
This study found an excess of acute myocardial infarction after occupational exposure to motor exhaust and evidence of dose-response. This is in contrast to an earlier analysis based on nitrogen dioxide as a marker and expert assessment rather than a JEM to assess exposure. The risk was higher among those with more recent exposure.