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Ozone is ubiquitous throughout the atmosphere and elevated levels (≥75 ppb) are common in large urban areas. Exposure to ground-level ozone can result in respiratory health effects. During 2008–2011, Sublette County (population ~10,000; 2.1 persons/mile2) had documented elevated ground-level ozone; we sought to determine if ground-level ozone concentrations were associated with respiratory-related clinic visits in Sublette County.
METHODS:
Respiratory-related clinic visits were ascertained from the only two area clinics’ electronic billing records for 2008–2011. The Wyoming Department of Environmental Quality provided daily ground-level ozone measurements and weather data. We used a bidirectional (before and after event) time-stratified (1-month) case-crossover design (each case serves as its own control), adjusted for temperature and humidity, to investigate associations between ground-level ozone concentrations and respiratory clinic visits. We examined interactions by age category and sex.
RESULTS:
The final data set included 12,742 case-days and 43,285 control-days. Females accounted for 52.7% (6,717) of the case-days. Median patient age was 28.6 years (range: 4 months–98 years). The median ground-level ozone concentration was 47 ppb (range: 19–84 ppb). For every 10 ppb ozone increase, in the following day, clinic visits increased by 4.8% (adjusted odds ratio: 1.048; 95% confidence interval: 1.003–1.095). Because of the limited sample size, we were unable to stratify by ozone season or year. We identified no other statistically significant interactions.
CONCLUSIONS:
Prior studies have not examined potential health effects of ground-level ozone in nonurban communities. Consistent with extant literature, our results indicate an association between ground-level ozone concentrations and respiratory clinic visits among persons residing in Sublette County. Education efforts can help the public limit their exposure and understand health effects of ozone.