Relationship between exposure to ozone and exacerbation requiring hospital admission among patients with asthma: a case-control study in central Taiwan

OBJECTIVE: The convergence of asthma and air pollutants in ageing populations is currently a growing health issue worldwide, and hence there is an essential need to investigate the association between exposure to air pollution, particularly ozone (O(3)), and exacerbation requiring admission in patients with asthma. SETTING: A case-control study at a tertiary referral hospital in central Taiwan. PARTICIPANTS: We used an asthma cohort, which included 11 400 patients with asthma, for the period 2006–2018 at Taichung Veterans General Hospital. PRIMARY AND SECONDARY OUTCOME MEASURES: We identified patients who had admitted for exacerbation as cases and selected patients with asthma without exacerbation, matching (1:4) the cases for age, gender and season of exacerbation, as controls. Data on hourly level of air pollutants were obtained from the Taiwan Environmental Protection Administration. We used conditional logistic regression and calculated adjusted ORs (adjORs) with 95% CIs. RESULTS: We enrolled 11 400 participants with asthma, and 4.4% (501) of them had been admitted for exacerbation. Participants with asthma with exacerbation requiring hospitalisation were exposed to a higher level of O(3) 8-hour daily maximum (adjOR 1.009, 95% CI 1.001 to 1.016) and were more likely to have high Charlson Comorbidity Index (CCI ≥3; adjOR 2.198, 95% CI 1.729 to 2.794) and asthma-chronic obstructive pulmonary disease overlap (adjOR 4.542, 95% CI 3.376 to 6.611) compared with those without exacerbation. The aforementioned associations between exacerbation of asthma requiring hospitalisation and exposure to O(3) were similar when defined by either O(3) 1-hour daily maximum or O(3) 24-hour average. Moreover, the O(3) relevant exacerbation of asthma mainly existed in those aged older than 65 years and patients with medical comorbidities, including gastrointestinal diseases, cardiovascular diseases, neurological diseases, diabetes and renal disease. CONCLUSIONS: Our findings highlight the need for vigilance of exposure to O(3) among elderly with asthma, particularly those with medical comorbidities. Further studies are warranted to investigate the underlying mechanisms.