Ozone pollution and asthma emergency department visits in Fresno, CA, USA, during the warm season (June–September) of the years 2005 to 2015: a time-stratified case-crossover analysis

Fresno, located at the central part of the San Joaquin Valley (SJV), CA, USA, is one of the most air-polluted cities in North America. The present time-stratified case-crossover study investigates whether short-term exposure to ozone (O₃) is associated with asthma emergency departments (ED) visits during the high O₃ warm seasons (June–September) of 2005 to 2015 in Fresno, CA, USA. A total of 4463 ED visits from 2005 to 2015 in Fresno were identified. The potential effect modification by land use (commercial and residential), sex, race (White, Black, and Hispanic), and age (2–5, 6–18, 19–40, 41–64, and > = 65) was investigated. A 5 ppb increase in the concentration of O₃ at the lag 0–14 was associated with 33.6% increase in the odds of having an asthma ED visit [OR 1.336 (95% confidence intervals 1.262, 1.414)]. People living in commercial areas (OR 1.470 (95% confidence intervals 1.353, 1.597) at lag 0–14) experienced higher odds of visiting the ED due to asthma when compared to those living in residential areas (OR 1.193 (95% confidence intervals 1.084, 1.313) at lag 0–14). Sex was not a modifier in this study. Blacks and Hispanics showed faster response to O₃ exposure. The association between O₃ exposure and asthma ED visits was positive among all age groups, but greater among 6 to 18 years. Ozone exposure is associated with asthma ED visits in Fresno during the warm seasons (June–September) of 2005 to 2015.