THE ROLE OF DURATION IN THE ASSOCIATION OF EXPOSURE TO TRAFFIC WITH THE ONSET OF MYOCARDIAL INFARCTION

ISEE-333 Introduction: An association between exposure to vehicular traffic in urban areas and the exacerbation of cardiovascular disease has been suggested in previous studies. We had shown earlier that exposure to traffic may trigger myocardial infarction (MI) within one hour of exposure. The current analysis aimed to evaluate if there is an effect of exposure duration. Methods: We conducted a case–crossover study in which cases of MI were identified with the use of data from the Cooperative Health Research in the Region of Augsburg Myocardial Infarction Registry in Augsburg, Germany, from February 1999 to July 2001. There were 691 subjects for whom the date and time of the MI were known, who had survived for at least 24 hours after the event, completed the registry's interview, and provided information on activities that may have triggered the MI in a patient diary. To assess the association of traffic exposure (time the subjects spent in cars, on public transportation, or on motorcycles or bicycles) with MI in conditional logistic regression analyses, the two hour-period before onset was considered as case period and intervals of the same length 24 and 48 before onset were defined as control periods. Number of hours spent in traffic over the 24 preceding hours were calculated and used to divide traffic exposures into three levels: (a) 1–2 hours, (b) 3–5 hours and (c) six hours or more of traffic exposure during the 24 previous hours. Results: Exposures to traffic were more frequent in the two hours before the event than in the control periods and more extended. 9.3 % of these exposed patients where in traffic for 1–2 hours during the 24 hours preceding the event compared to 4.9 % and 7.2 % in the control periods. 6.8 % where in traffic for 3–5 hours compared to 3.3% and 3.2% in the control periods. 2.4 % were exposed to traffic for six or more hours on the case day and 1.6% on each of the control days. Case-crossover analyses of the association of traffic exposure with MI resulted in an odds ratio (OR) of 2.78 (95% confidence interval (CI) 1.97 to 3.91), confirming our earlier findings, using a slightly different control selection strategy, effect period and including persons on travel outside the study area. Dividing this exposure of interest into duration categories yielded an OR of 2.3 (95% CI 1.53–3.46) for exposures of 1–2 hours total, 3.70 (95% CI 2.24–6.13) for cumulative exposures of 3–5 hours and 3.54 (95% CI 1.42–8.83) for six hours or more. Conclusion: The results suggest that the overall duration of exposures to traffic may have an impact on the triggering of myocardial infarction in susceptible persons.