Particulate Air Pollution and Hospital Admissions for Cardiac Diseases in Potentially Sensitive Subgroups

Background: Although numerous studies have provided evidence of an association between ambient air pollution and acute cardiac morbidity, little is known regarding susceptibility factors. Methods: We conducted a time-stratified case-crossover study in 9 Italian cities between 2001 and 2005 to estimate the short-term association between airborne particles with aerodynamic diameter <10 mu m (PM10) and cardiac hospital admissions, and to identify susceptible groups. We estimated associations between daily PM 10 and all cardiac diseases, acute coronary syndrome, arrhythmias and conduction disorders, and heart failure for 167,895 hospitalized subjects >= 65 years of age. Effect modification was assessed for age, sex, and a priori-defined hospital diagnoses (mainly cardiovascular and respiratory conditions) from the previous 2 years as susceptibility factors. Results: The increased risk of cardiac admissions was 1.0% (95% confidence interval [CI] = 0.7% to 1.4%) per 10 mu g/m(3) PM 10 at lag 0. The effect was slightly higher for heart failure (lag 0, 1.4% [0.7% to 2.0%]) and acute coronary syndrome (lag 0-1, 1.1% [0.4% to 1.9%]) than for arrhythmias (lag 0, 1.0% [0.2% to 1.8%]). Women were at higher risk of heart failure (2.0% [1.2% to 2.8%]; test for interaction, P = 0.022), whereas men were at higher risk of arrhythmias (1.9% [0.8% to 3.0%]; test for interaction, P = 0.020). Subjects aged 75-84 years were at higher risk of admissions for coronary events (2.6% [1.5% to 3.8%]; test for interaction, P = 0.001). None of the identified chronic conditions was a clear marker of susceptibility. Conclusions: An important effect of PM 10 on hospitalizations for cardiac diseases was found in Italian cities. Sex and older age were susceptibility factors.