Impact of short-term exposure to fine particulate matter on emergency ambulance dispatches in Japan

Background Evidence of an association between fine particulate matter (PM2.5) and morbidity is limited in Asia. We used a case-crossover design to evaluate the association between short-term exposure to PM2.5 and emergency ambulance dispatches (as a proxy of acute health outcomes), and to calculate the extent to which a 10 mu g/m(3) decrease in PM2.5 concentrations would reduce the number of ambulance dispatches. Methods We used data on emergency ambulance dispatches in Fukuoka City, Japan between 2005 and 2010. Emergency ambulance services are publicly funded and cover the entire city. After excluding ambulance dispatches related to external injuries and pregnancy/childbirth, we analysed data on the remaining 176 123 dispatches. We also collected records of daily concentrations of PM2.5 from one ambient air pollution monitoring station. ORs per 10 mu g/m(3) increase in PM2.5 were estimated using conditional logistic regression controlled for ambient temperature and relative humidity. Results During the study period, the average daily concentration of PM2.5 was 20.3 mu g/m(3). Exposure to PM2.5 was associated with emergency ambulance dispatches in general (lag0-1; OR=1.008 (95% CI 1.002 to 1.014)) and with dispatches due to respiratory diseases (lag0-1; OR=1.027 (1.007 to 1.048)). No association was observed for dispatches due to cardiovascular diseases. We estimated that a 10 mu g/m(3) decrease in PM2.5 concentrations would have led to approximately 260 (estimated range=70-460) fewer ambulance dispatches in Fukuoka for 2012. Conclusions Providing further evidence on the short-term health effects of PM2.5 exposure, we found that exposure was associated with an increased number of emergency ambulance dispatches. The effect was, however, relatively small.