Efficacy of Air Filtration and Education Interventions on Indoor Fine Particulate Matter and Child Lower Respiratory Tract Infections among Rural U.S. Homes Heated with Wood Stoves: Results from the KidsAIR Randomized Trial

Background: Millions of rural U.S. households are heated with wood stoves. Wood stove use can lead to high indoor concentrations of fine particulate matter [airborne particles $\le 2.5\mu m$ in aerodynamic diameter (${\mathrm{PM}}_{2.5}$)] and is associated with lower respiratory tract infection (LRTI) in children.

Objectives: We assessed the impact of low-cost educational and air filtration interventions on childhood LRTI and indoor ${\mathrm{PM}}_{2.5}$ in rural U.S. homes with wood stoves.

Methods: The Kids Air Quality Interventions for Reducing Respiratory Infections (KidsAIR) study was a parallel three-arm (education, portable air filtration unit, control), post-only randomized trial in households from Alaska, Montana, and Navajo Nation (Arizona and New Mexico) with a wood stove and one or more children $<5\text{years}$ of age. We tracked LRTI cases for two consecutive winter seasons and measured indoor ${\mathrm{PM}}_{2.5}$ over a 6-d period during the first winter. We assessed results using two analytical frameworks: a) intervention efficacy on LRTI and ${\mathrm{PM}}_{2.5}$ (intent-to-treat), and b) association between ${\mathrm{PM}}_{2.5}$ and LRTI (exposure-response).

Results: There were 61 LRTI cases from 14,636 child-weeks of follow-up among 461 children. In the intent-to-treat analysis, children in the education arm [$\text{odds ratio}\left(\text{OR}\right)=0.98$; 95% confidence interval (CI): 0.35, 2.72] and the filtration arm ($\text{OR}=1.23$; 95% CI: 0.46, 3.32) had similar odds of LRTI vs. control. Geometric mean ${\mathrm{PM}}_{2.5}$ concentrations were similar to control in the education arm (11.77% higher; 95% CI: $-16.57$, 49.72) and air filtration arm (6.96% lower; 95% CI: $-30.50$, 24.55). In the exposure-response analysis, odds of LRTI were 1.45 times higher (95% CI: 1.02, 2.05) per interquartile range ($25{\mu g/m}^3$) increase in mean indoor ${\mathrm{PM}}_{2.5}$.

Discussion: We did not observe meaningful differences in LRTI or indoor ${\mathrm{PM}}_{2.5}$ in the air filtration or education arms compared with the control arm. Results from the exposure-response analysis provide further evidence that biomass air pollution adversely impacts childhood LRTI. Our results highlight the need for novel, effective intervention strategies in households heated with wood stoves. https://doi.org/10.1289/EHP9932.