Background:Daily air pollution is associated with increased hospital admissions for cardiovascular diseases, but there are few observations on the link with acute myocardial infarction. To evaluate the relation between various urban air pollutants (total suspended particulate, SO2, CO, NO2) and hospital admissions for acute myocardial infarction in Rome, Italy, we performed a case-crossover analysis and studied whether individual characteristics act as effect modifiers.Methods:We studied 6531 subjects residing in Rome and hospitalized for a first episode of acute myocardial infarction (International Classification of Diseases, 9thedition: 410) from January 1995 to June 1997. The following individual information was available: sex, age, date of hospitalization, coexisting illnesses (hypertension, 25%; diabetes, 15%), and cardiac severity (conduction disorders, 6%; cardiac dysrhythmias, 20%; heart failure, 11%). Daily air pollution data were taken from 5 city monitors. We used a time-stratified case-crossover design; control days were the same day of the week as the myocardial infarction occurred, in other weeks of the month.Results:Positive associations were found for total suspended particulate, NO2and CO. The strongest and most consistent effect was found for total suspended particulate. The odds ratio (OR) associated with 10 &mgr;g/m3of total suspended particulate over the 0- to 2-day lag was 1.028 (95% confidence interval [CI] = 1.005–1.052). The association with total suspended particulate tended to be stronger among people older than 74 years of age (OR = 1.046; CI = 1.005–1.089), in the warm period of the year (OR = 1.046; CI = 1.008–1.087), and among subjects who had heart conduction disorders (OR = 1.080; CI = 0.987–1.181).Conclusions:The results suggest that air pollution increases the risk of myocardial infarction, especially during the warm season. There was a tendency for a stronger effect among the elderly and people with heart conduction disturbances.