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Abstract

Background: Ambient air pollution, particularly fine particulate matter (PM₂.₅), is an increasing concern in British Columbia (BC), Canada, due to more severe and frequent wildfires. While links between air pollution and asthma-related morbidity are well-established, its role in adult-onset asthma remains less clear. Evidence on the cost-effectiveness of interventions, such as portable HEPA air cleaners, is also limited. Objective: This thesis aimed to 1) summarize epidemiological evidence on the relationship between ambient air pollution and adult asthma incidence, and 2) evaluate the cost-effectiveness of a provincial rebate program for HEPA air cleaners in reducing asthma and related adverse health outcomes in BC. Methods: A systematic review and meta-analysis were conducted on studies evaluating outdoor air pollution and adult asthma incidence. Pooled risk estimates from this review, along with additional published data, were applied to a Markov cost-effectiveness model of a HEPA air cleaner rebate program. The model simulated a general population cohort under future wildfire-related PM₂.₅ exposure scenarios to estimate asthma incidence, exacerbations, and costs across BC’s Health Service Delivery Areas (HSDAs). Result: Twenty-five studies met inclusion criteria. Each 5 µg/m³ increase in PM₂.₅ was associated with a 7% higher risk of adult asthma (RR 1.07, 95% CI 1.01–1.13), and each 10 µg/m³ increase in NO2 was linked to an 11% higher risk (RR 1.11, 95% CI 1.03–1.20). No significant associations were observed for O3 or SO2. Substantial heterogeneity was present across studies. In the cost-effectiveness model, wildfire-derived PM₂.₅ was estimated to cause 13–14 new asthma cases per 100,000 person-years annually (2023–2036). A $150 rebate reduced exacerbations but was not cost-effective (ICERs $149,408–154,749/QALY). A $100 rebate was cost-effective in three HSDAs, while a $50 rebate was cost-effective in all HSDAs. Conclusions: Ambient PM₂.₅ and NO₂ may contribute to the development of adult asthma, highlighting the need for continued epidemiologic research with consistent methods. A $100 rebate was cost-effective in three HSDAs, whereas a $50 rebate was cost-effective across all HSDAs. Broader benefits across multiple health outcomes, which were not captured here, may further improve the value of air cleaners and warrant future study.