Seasonal Effect of Fine and Ultrafine Particles on Hospitalization for Cardiac and Respiratory Diseases

Abstract

ISEE-497 Objective: We examined whether the association of daily concentration of fine and ultrafine particles with hospital admissions for cardiac and respiratory diseases changes according to season. Material and Methods: Daily data on cardiac and respiratory hospital admissions and fine (PM2.5) and ultrafine particles [measured as particles number concentration (PNC)] were collected in Rome during the period 2001 to 2005. Three seasons were defined: winter (December–March), summer (June–September), and spring/fall (April, May, October, November). A case-crossover design was adopted for each season where control days were selected according to the time stratified approach with adjustment for various time-related confounders. The results are expressed as percentage increase in admissions per 10 μg/m3 PM2.5 and 9618 particles/cm3. Results: Daily levels of particles varied substantially by season, with higher PM2.5 and PNC levels in winter than in summer or in the spring/fall. PM2.5 was associated with admissions for cardiac diseases at lag 0 in winter (1.77%, 95%CI = 0.85–2.69) and in spring/fall (1.62%, 95%CI = 0.18–3.08) but not in summer; on the other hand, the strongest effect of PM2.5 on respiratory diseases was in summer (lag 0): 6.32% (95%CI = 0.22–12.79) for COPD; 21.74% (95%CI = 3.96–42.56) for asthma. The effect of PNC showed a delayed effect for cardiac diseases only in summer (2.43% at lag 2), and an association with COPD admissions at lag 0 was found in winter (1.73%, 95%CI = 0.02–3.47) and in spring/fall (2.99%, 95%CI = 0.52–5.52). Conclusions: The effects of fine and ultrafine particles vary by season. PM2.5 and PNC both had a cardiac effect during winter at immediate lag, but PNC also had a delayed effect during summer. PM2.5 had the largest respiratory.