Association between PM₁₀ from vegetation fire events and hospital visits by children in upper northern Thailand

Few studies have focused on the effects of exposure to air pollutants from vegetation fire events (including forest fire and the burning of crop residues) among children. In this study we aimed to investigate the association between PM₁₀ concentrations and hospital visits by children to address respiratory disease, conjunctivitis, and dermatitis. We examined and compared these associations by the presence of vegetation fire events on a given day (burning, non-burning, and mixed) across the upper northern region of Thailand from 2014 through 2018. A vegetation burning was defined when a fire hotspot (obtained from NASA-MODIS) exceeded the 90th percentile of the entire region and PM₁₀ concentration was over 100 μg/m³. To determine the association between hospital visits among children with PM₁₀ concentrations on burning and non-burning days, we performed a time-stratified case-crossover analysis fitted with conditional logistic regression for each province. A random-effects meta-analysis was applied to pool province-specific effect estimates. The number of burning days ranged from 64 to 139 days across eight provinces. A 10 μg/m³ increase in PM₁₀ concentration on a burning day was associated with a respiratory disease-related hospital visit at lag 0 (OR = 1.01 (95% CIs: 1.00, 1.02)). This association was not observed for hospital visits related to conjunctivitis and dermatitis. A positive association was also observed between PM₁₀ concentration on non-burning days and hospital visits related to respiratory disease at lag 0 (OR = 1.03 (95% CIs: 1.02, 1.04)). Hospital visits for conjunctivitis and dermatitis were significantly associated with PM₁₀ concentration at lag 0 on both non-burning and mixed days