Objectives: We evaluated the association between concentration of particulate matter below 10 microns (PM10) and out-of-hospital coronary deaths in eight Italian cities during 1997-2004, investigating the role of individual effect-modifiers.
Methods: A total of 16,989 subjects over 35 years who died out-of-hospital from coronary causes (ICD-9: 410-414) were studied; for each individual, hospital admissions in the previous two years were identified using record-linkage procedures. Daily PM10 values from urban monitoring stations were available and we studied the effect of the mean of current and previous day levels (lag 0-1). A city-specific case-crossover analysis was applied using a time-stratified approach while considering as confounders weather, holidays, influenza epidemics, and the summer decrease in the population. The pooled percentage increase (and 95% CI) in mortality per 10 µg/m3 of PM10 was estimated.
Results: A significant increase in out-of-hospital coronary deaths in relation to a 10 µg/m3 increase in PM10: 1.46% (95% CI: 0.50; 2.43). Although no statistically significant effect modification by age was found, the effect was stronger among subjects 65 years (1.60%, 0.59; 2.63), in particular among those aged 65-74 (3.01%, 0.74; 5.34). People in the lowest socio-economic status category (3.34%, 1.28; 5.45) had a stronger effect than those in the highest category. No clear effect modification was seen for gender, season, or any specific comorbidity. An indication of negative effect modification was seen for persons with previous admission for cardiac dysrhythmias. Subjects without hospital admissions in the previous two years were slightly more affected by PM10 effects (1.91%, 0.28; 3.47) than those with at least one previous hospital admission (1.44%, 0.09; 2.82).
Conclusions: Our results show that short-term exposure to PM10 has a strong effect on coronary mortality, greater among the elderly and socio-economically disadvantaged people. No clear effect modification by previous hospitalizations was detected, except for cardiac dysrhythmias possibly due to a protective treatment.
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