Is short-term exposure to ambient fine particles associated with measles incidence in China? A multi-city study

Background: China's rapid economic development has resulted in severe particulate matter (PM) air pollution and the control and prevention of infectious disease is an ongoing priority. This study examined the relationships between short-term exposure to ambient particles with aerodynamic diameter <= 2.5 mu m (PM2.5) and measles incidence in China. Methods: Data on daily numbers of new measles cases and concentrations of ambient PM2.5 were collected from 21 cities in China during Oct 2013 and Dec 2014. Poisson regression was used to examine city-specific associations of PM2.5 and measles, with a constrained distributed lag model, after adjusting for seasonality, day of the week, and weather conditions. Then, the effects at the national scale were pooled with a random-effect meta-analysis. Results: A 10 mu g/m(3) increase in PM2.5 at lag 1 day, lag 2 day and lag 3 day was significantly associated with increased measles incidence [relative risk (RR) and 95% confidence interval (CI) were 1.010 (1.003, 1.018), 1.010 (1.003, 1.016) and 1.006 (1.000, 1.012), respectively]. The cumulative relative risk of measles associated with PM2.5 at lag 1-3 days was 1.029 (95% CI: 1.010, 1.048). Stratified analyses by meteorological factors showed that the PM2.5 and measles associations were stronger on days with high temperature, low humidity, and high wind speed. Conclusions: We provide new evidence that measles incidence is associated with exposure to ambient PM2.5 in China. Effective policies to reduce air pollution may also reduce measles incidence.