Seasonal distribution of acute myocardial infarction and its relation to acute infections in a mild climate.

BACKGROUND There is evidence that acute myocardial infraction (aMI) occurs more frequently in certain seasons and months of the year. Recently various infectious agents have been implicated in atherogenesis. In the present study we recorded the seasonal distribution of aMI and evaluated its relation to acute systemic infections (AIs). METHODS The study included 1196 patients with aMI hospitalized during the years 1988-1998 in the General Hospital of the island of Rhodes and 2976 patients with AI during the years 1993-1998. Foreigners or visitors in the island were excluded to avoid their influence in the annual distribution. We corrected the absolute number of the aMI and AI cases by month and season in such a way that all months and seasons would have standard 30 and 90 days, respectively. RESULTS During the entire period of the study, more patients with aMI were hospitalized in winter [30.7%, 95% confidence limits (CL) 28.1 to 33.3%]. In spring the percentage of aMI cases hospitalized was 24.5% (CL 22.1-27%), in summer 23.2% (CL 20.1-25.6%) and in autumn 21.6% (CL 19.2 -24%). There were 42.35% more cases hospitalized in winter than in autumn. The monthly distribution showed that March was the month with the most aMI cases (10.83%, CL 9.06-12.6% ) and October with the fewest (6%, CL 4.65-7.35%). The percentage of patients with AI hospitalized in winter was 30.5% (CL 28.8-32.2%), in spring 25.2% (23.6-26.7), in summer 23.5% (CL 22-25%) and in autumn 20.8% (CL 19.4-22.3%). The correlation coefficient (r) between the distribution of aMI and AI was 0.73 (P<0.01). CONCLUSIONS Our results indicate that (1) there is a seasonal distribution in aMI with the winter being the season of the highest incidence of aMI and autumn of the lowest and (2) there is a significant correlation of the distribution of aMI to AI cases, which is of interest in the understanding of the pathogenesis of acute coronary syndromes.