Relationships between weather and myocardial infarction: a biometeorological approach

Objectives: To calculate threshold values of weather discomfort which increase the risk of hospital admissions for myocardial infarction in winter and summer. Background: Notwithstanding heat waves were reported to acutely increase hospital admissions for cardiovascular diseases, large surveys failed to reveal any increase of event rates with increasing air temperature. However, the assessment of air temperature does not allow evaluation of the actual discomfort perception caused by the combination of different meteorological parameters. Methods: Hospital admissions for myocardial infarction for the period 1998-2002 in Florence, Italy, were considered. The percentages of variation of daily event rates according to daily mean air temperature variations were preliminary derived by using a regression analysis. An alternative biometeorological approach, considering the Apparent Temperature Index (ATI) in summer, and the New U.S./ Canada Wind Chill Temperature Index (NWCTI) in winter, which combine air temperature, relative humidity and wind velocity, was then used. Results: The traditional approach showed that daily event rates significantly increased with daily mean air temperature decrease (10 8C decrease were associated with 19% increase in daily event rates for people older than 65 years), but failed to show any negative effect caused by hot climatic conditions. Conversely the biometeorological approach allowed to show that at least 9 h per day of severe discomfort caused by hot conditions significantly increased the rate of admission ( P b0.01). Conclusions: This approach might be useful for the development of an operative weather watch/warning system for population and for hospital professional care.