HEPA Air Filters for Preventing Wildfire-Related Asthma Complications, a Cost-effectiveness Study
Authors: Adibi Amin , Barn Prabjit , Shellington Erin M , Harvard Stephanie , Johnson Kate M , Carlsten Christopher 
Published: April 2023

Rationale

Air pollution caused by wildfire smoke is linked to adverse health outcomes, especially for people living with asthma. We studied whether government rebates for high-efficiency particulate air (HEPA) filters, which reduce smoke particles indoors, are cost-effective in managing asthma and preventing exacerbations in British Columbia (BC), Canada.

Methods

A Markov model analyzed health states for asthma control, exacerbation severity, and death over a retrospective time-horizon of 5 years (2018-2022). Wildfire smoke-derived particulate matter (PM2.5) from the CanOSSEM model and relevant literature informed the model. The base case analysis assumed continuous use of the HEPA filter. Costs and quality-adjusted life-years (QALYs) resulting from varying rebates were computed for each Health Service Delivery Area (HSDA).

Results

In the base case analysis, HEPA air filter use resulted in increased costs of $83.34 (SE=1.03) and increased QALYs of 0.0011 (SE=0.0001) per person. Average incremental cost effectiveness ratio (ICER) among BC HSDAs was $74,652/QALY (SE=3,517), with ICERs ranging from $40,509 to $89,206 per QALY in HSDAs. Across the province, the intervention was projected to prevent 4,418 exacerbations requiring systemic corticosteroids, 643 emergency department visits, and 425 hospitalizations during the 5-year time horizon. A full rebate was cost-effective in one of the 16 HSDAs across BC. The probability of cost-effectiveness ranged from 0.1% to 74.8% across HSDAs. A $100 rebate was cost-effective in most HSDAs.

Conclusions

Our results indicate variable cost-effectiveness of HEPA filters in managing wildfire smoke-related asthma issues in BC. The effectiveness of government rebates varies by region but rebates up to two-thirds of the filter cost generally appear cost-effective, with a full rebate only cost-effective in Kootenay Boundary.

Lay Summary

Wildfire smoke can increase flare ups of symptoms among people living with asthma. These flare ups may require a visit to the emergency department or hospital admission. Research shows that portable HEPA air filters can significantly reduce concentrations of fine particles (PM2.5, an important component of wildfire smoke) in homes and other buildings. Using air filters during smoke events is a common public health recommendation. However, air filters are not accessible to everyone, with units costing anywhere between $150 to a few hundred dollars. Does it make sense for the government of BC to offer a rebate on the cost of purchasing air filters for every person living with asthma in BC? In this study, we used historical data on wildfire smoke concentrations between 2018 to 2022, computer simulations, and health economics methods to answer this question. Our results suggest that it is likely cost-effective for the government to pay for a portion of the costs of air filters, particularly in the interior and northern interior parts of BC. We also looked at other scenarios, such as filter use only when outdoor pollution exceeds certain thresholds that typically trigger an air quality advisory. We found that a $100 rebate was cost-effective when the air filter was used continuously, whereas a $30 rebate was cost-effective when the air filter was turned on only during air quality advisories.