Environ Res

ObjectiveWe investigated associations of short-term changes in ambient ozone (O3), fine particulate matter (PM2.5) and nitrogen dioxide (NO2) concentrations and the timing of new-onset asthma, using a large, high-risk population in an area with historically high ozone levels.MethodsThe study population included 18,289 incident asthma cases identified among Medicaidenrolled children in Harris County Texas between 2005\u20132007, using Medicaid Analytic Extract enrollment and claims files. We used a time-stratified case-crossover design and conditional logistic regression to assess the effect of increased short-term pollutant concentrations on the timing of asthma onset.ResultsEach 10 ppb increase in ozone was significantly associated with new-onset asthma during the warm season (May\u2013October), with the strongest association seen when a 6-day cumulative average period was used as the exposure metric (odds ratio [OR]=1.05, 95% confidence interval [CI], 1.02\u20131.08). Similar results were seen for NO2 and PM2.5 (OR=1.07, 95% CI, 1.03\u20131.11 and OR =1.12, 95% CI, 1.03\u20131.22, respectively), and PM2.5 also had significant effects in the cold season (November\u2013April), 5-day cumulative lag (OR=1.11. 95% CI, 1.00\u20131.22). Significantly increased ORs for O3 and NO2 during the warm season persisted in co-pollutant models including PM2.5. Race and age at diagnosis modified associations between ozone and onset of asthma.ConclusionOur results indicate that among children in this low-income urban population who developed asthma, their initial date of diagnosis was more likely to occur following periods of higher short-term ambient pollutant levels.T42 OH008421/OH/NIOSH CDC HHSUnited States/T42OH008421/ACL/ACL HHSUnited States/2T42OH008421/OH/NIOSH CDC HHSUnited States