• Kerry R Pride, Jennifer L Peel, Byron F Robinson, Ashley Busacker, Joseph Grandpre, Kristine M Bisgard, Fuyuen Y Yip, and Tracy D Murphy.
• Epidemic Intelligence Service, Centers for Disease Control and Prevention, Atlanta, GA, USA; Wyoming Department of Health, 6101 Yellowstone Road, Suite 510, Cheyenne, WY 82002, USA. Electronic address: hgp3@cdc.gov.
• Environ. Res. 2015 Feb 1; 137: 1-7.

ObjectiveShort-term exposure to ground-level ozone has been linked to adverse respiratory and other health effects; previous studies typically have focused on summer ground-level ozone in urban areas. During 2008-2011, Sublette County, Wyoming (population: ~10,000 persons), experienced periods of elevated ground-level ozone concentrations during the winter. This study sought to evaluate the association of daily ground-level ozone concentrations and health clinic visits for respiratory disease in this rural county.MethodsClinic visits for respiratory disease were ascertained from electronic billing records of the two clinics in Sublette County for January 1, 2008-December 31, 2011. A time-stratified case-crossover design, adjusted for temperature and humidity, was used to investigate associations between ground-level ozone concentrations measured at one station and clinic visits for a respiratory health concern by using an unconstrained distributed lag of 0-3 days and single-day lags of 0 day, 1 day, 2 days, and 3 days.ResultsThe data set included 12,742 case-days and 43,285 selected control-days. The mean ground-level ozone observed was 47 ± 8 ppb. The unconstrained distributed lag of 0-3 days was consistent with a null association (adjusted odds ratio [aOR]: 1.001; 95% confidence interval [CI]: 0.990-1.012); results for lags 0, 2, and 3 days were consistent with the null. However, the results for lag 1 were indicative of a positive association; for every 10-ppb increase in the 8-h maximum average ground-level ozone, a 3.0% increase in respiratory clinic visits the following day was observed (aOR: 1.031; 95% CI: 0.994-1.069). Season modified the adverse respiratory effects: ground-level ozone was significantly associated with respiratory clinic visits during the winter months. The patterns of results from all sensitivity analyzes were consistent with the a priori model.ConclusionsThe results demonstrate an association of increasing ground-level ozone with an increase in clinic visits for adverse respiratory-related effects in the following day (lag day 1) in Sublette County; the magnitude was strongest during the winter months; this association during the winter months in a rural location warrants further investigation.Published by Elsevier Inc.

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