LAUSR

Background: Studies have reported protective and adverse associations between microbial exposure and childhood asthma. However, among children with asthma the relationships between endotoxin and exercise‐induced bronchospasm (EIB) is less clear. Objective: We investigated the association between exposure to endotoxin in house dust with atopy and EIB in children with asthma. Methods: A cross‐sectional survey was conducted among schoolchildren (aged 7–17 years) in the province of Saskatchewan, Canada. A subpopulation with asthma (n = 116) were identified from 335 participants using a validated asthma algorithm. We determined atopy among the asthma subpopulation by skin prick testing (SPT) while EIB was evaluated using exercise challenge testing (ECT). Dust samples were collected from mattress and play area floors, and endotoxin was measured in dust extracts. Logistic regression analyses were used to explore associations between endotoxin with atopy and EIB. Results: Among the 116 children with asthma, 99 completed SPT and all had completed ECT. Of these, 71/99 (71.7%) were atopic and 26/116 (22.4%) had EIB. Exposure to high play area endotoxin concentration [adjusted odds ratio (aOR) = 0.15, 95% CI: 0.03–0.85] and load (aOR = 0.11, 95% CI: 0.02–0.73) were negatively associated with atopy. In contrast, EIB was positively associated with high mattress endotoxin concentration (aOR = 6.01, 95% CI: 1.20–30.13). Conclusion: Indoor microbial endotoxin exposure has varied associations with atopy and exercise‐induced bronchospasm among children with asthma.