Short-term effects of air pollution on out-of-hospital cardiac arrest in Stockholm

Although ozone (O3) and other pollutants have been associated with cardiovascular morbidity and mortality, the effects of O3 on out-of-hospital cardiac arrest (OHCA) have rarely been addressed and existing studies have presented inconsistent findings. The objective of this study was to determine the effects of short-term exposure to air pollution including O3 on the occurrence of OHCA, and assess effect modification by season, age, and gender. A total of 5973 Emergency Medical Service-assessed OHCA cases in Stockholm County 2000–10 were obtained from the Swedish cardiac arrest register. A time-stratified case-crossover design was used to analyse exposure to air pollution and the risk of OHCA. Exposure to O3, PM2.5, PM10, NO2, and NOx was defined as the mean urban background level during 0–2, 0–24, and 0–72 h before the event and control time points. We adjusted for temperature and relative humidity. Ozone in urban background was associated with an increased risk of OHCA for all time windows. The respective odds ratio (confidence interval) for a 10 µg/m3 increase was 1.02 (1.01–1.05) for a 2-h window, 1.04 (1.01–1.07) for 24-h, and 1.05 (1.01–1.09) for 3 day. The association with 2-h O3 was stronger for events that occurred outdoors: 1.13 (1.06–1.21). We observed no effects for other pollutants and no effect modification by age, gender, or season. Short-term exposure to moderate levels of O3 is associated with an increased risk of OHCA.