Abstract
The association of outdoor air pollution and meteorological elements with primary care visits at night due to asthma attack was studied. A case-crossover study was conducted in a primary care clinic in Himeji City, Japan. The subjects were 956 children aged 0-14 years who visited the clinic with an asthma attack between the hours of 9 p.m. and 6 a.m. Daily concentrations of particulate matter, ozone, nitrogen dioxide, and a number of meteorological elements were measured, and a conditional logistic regression model was used to estimate odds ratios (ORs) of primary care visits per unit increment of air pollutants or meteorological elements. The analyses took into consideration the effects of seasonality. Of the 956 children, 73 (7.6 %) were aged <2 years and 417 (43.6 %) were aged 2-5 years. No association between daily ozone levels and primary care visits due to asthma attack at night in the spring or summer was found. An inverse relation between suspended particulate matter and primary care visits due to asthma attack was detected in the winter. ORs in the summer per degree increment in daily mean temperature was 1.31 [95 % confidential interval (CI) 1.09-1.56], and ORs in the autumn per hourly increment in daily hours of sunshine was 0.94 (95 % CI 0.90-0.99). The findings of our study fail to support any association between daily mean concentration of air pollutant and primary care visits at night. However, we did find evidence indicating that certain meteorological elements may be associated with primary care visits.
Highlights
To ascertain whether there is an association between ambient air pollution/meteorological factors and primary care visits at night due to asthma, we examined these factors among children with a past history of asthma attack who had visited the municipal emergency primary care clinic in Himeji, an industrial city in the western part of Japan, between 9 p.m. and 6 a.m. at some point between 1 April 2010 and 31 March 2012
We noted no association between 1-day ozone levels and primary care visits due to asthma attack at night in the summer, nor did we note any association between other air pollutants and primary care visits, except for an inverse relation between ozone and suspended PM (SPM) and primary care visit due to asthma attack in the winter season
We did find evidence indicating that several meteorological elements, such as temperature and hours of daylight, may be associated with primary care visits due to asthma attack
Summary
The setting of this study was Himeji City Emergency Clinic, Himeji, Japan, which had been established for the purpose of treating emergency cases between 9 p.m. and 6 a.m. on weekdays. The subjects of our study were city residents aged 0–14 years with a past history of asthma attack who had visited the municipal emergency primary care clinic between 9 p.m. and 6 a.m. at some point between 1 April 2010 and 31 March 2012. We examined associations between daily mean concentrations of each air pollutant and the risk of primary care visits at night due to asthma attack. These concentrations were subject-specific values averaged over the day of the indexing. We estimated ORs of primary care visits at night due to asthma attack per 10 lg/m3 difference in SPM, per 10 ppb difference in NO2, and per 10 ppb difference in ozone in a multi-pollutant model adjusted for the same variables as the single-pollutant model. We did not devise any countermeasures for these issues as we believed that elevated risks of air pollutants in this study should be demonstrated by the precautionary principle
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