Association between PM2.5 and primary care visits due to asthma attack in Japan: relation to Beijing’s air pollution episode in January 2013

In January 2013, extremely high concentrations of fine particles (PM2.5) were observed around Beijing, China. In Japan, the health effects of transboundary air pollution have been a matter of concern. We examined the association between the levels of outdoor PM2.5 and other air pollutants with primary care visits (PCVs) at night due to asthma attack in Himeji City, western Japan. A case–crossover study was conducted in a primary care clinic in Himeji City, Japan, involving 112 subjects aged 0–80 years who visited the clinic due to an asthma attack between 9 p.m. and 6 a.m. during the period January–March, 2013. Daily concentrations of particulate matter, ozone, nitrogen dioxide, and some meteorological elements were measured, and a conditional logistic regression model was used to estimate the odds ratios (OR) of PCVs per unit increment in air pollutants or meteorological elements. Of the 112 subjects, 76 (68 %) were aged