Ozone pollution and asthma emergency department visits in the Central Valley, California, USA, during June to September of 2015: a time-stratified case-crossover analysis

Abstract

Objective: The San Joaquin Valley (SJV) exceeds the state and national standards for ozone (O₃). This study investigates whether short-term exposure to O₃ is associated with asthma emergency department (ED) visits. Methods: We identified 1,101 ED visits in June–September of 2015 in SJV, California, who lived within 15 km of active air monitors. Conditional logistic regression models were used to obtain the odds ratio (OR) and 95% confidence interval (CI) associated with an interquartile (IQR) increase in ozone. We explored the potential effect modification by sex (female and male), race (White, Black and Hispanic), age (2–5, 6–18, 19–40, 41–64 and > = 65) and county (Merced, Madera, Kings, Fresno and Kern). Results: An IQR range (18.1 ppb) increase in O₃ exposure three days before an asthma attack (lag 3) was associated with a 6.6% [OR: 1.066 (95% CI: 1.032, 1.082)] increase in the odds of having an asthma ED visit. The overall ORs differed across age groups and races/ethnicities, with strongest for children aged 6–18 years [OR: 1.219 (95% CI: 1.159, 1.280)], adults 19–40 years [OR: 1.102 (95% CI: 1.053, 1.154)] and Blacks [OR: 1.159 (95% CI: 1.088, 1.236)], respectively. O₃ exposure was not positively associated with asthma ED visits for Whites, while it was for other underrepresented groups. Fresno had the highest number of asthma ED visits and positive association among all five counties. Conclusion: We found that O₃ exposure is associated with asthma ED visits in the SJV.

Keywords:

• Asthma attacks
• air pollution
• ozone exposure
• conditional logistic regression
• San Joaquin Valley
• California

Acknowledgements

We would like to thank the California's Office of Statewide Health Planning and Development (OSHPD) for providing us with the data; and, those who helped us conducting this research. We would also like to thank Mr. Vicente Ramirez for creating Figures 2, 3 and 4.

Disclosure statement

The authors declare that they have no conflict of interest.

Ethics approval and consent to participate

The study was approved by the State of California Committee for the Protection of Human Subjects. The data used in this analysis does not contain any personal identifiable information. Informed consent was not required because data were anonymous. Additional safeguards included physical and electronic barriers to data access and encryption.