Association between ambient fine particulate matter and adult outpatient visits for rheumatoid arthritis in Beijing, China.

The association between fine particulate matter (PM 2.5 ) and rheumatoid arthritis (RA) is currently unclear, especially in Beijing, a city with severe air pollution. Our study aimed to explore the relationship between short-term outdoor exposure to PM 2.5 and RA outpatient visits using a time-series analysis in Beijing. We used the Beijing's Medical Claims for Employees database to identify patients with RA in 2010-2012. A generalized additive model with a Poisson link was used to estimate the percentage change in RA outpatient visits after the PM 2.5 concentration increased by 10 μg/m 3 . From January 1, 2010, to June 30, 2012, a total of 541,061 RA outpatient visits were identified. During the study period, the average daily (standard deviation) concentration of PM 2.5 was 99.5 (75.3) µg/m 3 . A 10 µg/m 3 increase in PM 2.5 concentration was correlated with a 0.21% (95% CI, 0.18-0.23%) increase in outpatient visits for RA on the same day. A significant association for the cumulative effect of PM 2.5 was found, and the largest significant association was observed for a lag of 0-3 days (0.26%; 95% CI, 0.23-0.29%). Stratified analyses revealed that females (0.29%, 95% CI: 0.26-0.33%) and 18-65 years old patients (0.29%, 95% CI: 0.25-0.32%) were most susceptible to the effects of PM 2.5 exposure. The current findings showed that short-term exposure to PM 2.5 was followed by an increase in the number of outpatient visits for RA in Beijing. Future studies should investigate the mechanisms underlying this association.