Contents lists available at ScienceDirect Environmental Research journal homepage: www.elsevier.com/locate/envres The association between endotoxin in house dust with atopy and exercise- induced bronchospasm in children with asthma Oluwafemi Oluwole a,b, ⁎ , Donna C. Rennie b,c , Ambikaipakan Senthilselvan d , Roland Dyck b,e , Anna Afanasieva b , Shelley Kirychuk b,e , George Katselis b,e , Joshua A. Lawson b,e a Department of Community Health and Epidemiology, University of Saskatchewan, 104 Clinic Place, Saskatoon, SK, Canada S7N 2Z4 b Canadian Centre for Health and Safety in Agriculture, College of Medicine, University of Saskatchewan, 104 Clinic Place, PO Box 23, Saskatoon, SK, Canada S7N 2Z4 c College of Nursing, University of Saskatchewan, 104 Clinic Place, Saskatoon, SK, Canada S7N 2Z4 d School of Public Health, University of Alberta, 11405 – 87 Ave, Edmonton, Alberta, Canada T6G 1C9 e Department of Medicine, College of Medicine, University of Saskatchewan, 103 Hospital Drive, Saskatoon, SK, Canada S7N 0W8 ARTICLE INFO Keywords: Asthma Atopic sensitization Exercise-induced bronchospasm Endotoxin Schoolchildren ABSTRACT Background: Studies have reported protective and adverse associations between microbial exposure and child- hood 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 as- sociated 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. 1. Introduction Indoor microbial exposure has been suggested to influence the presence of respiratory disorders, including childhood asthma (Kanchongkittiphon et al., 2015) but the associations are conflicting. Bacterial endotoxin has been reported to have protective (Tischer et al., 2011; Lawson et al., 2012), adverse (Tavernier et al., 2005; Thorne et al., 2005; Chinn and Williams, 2007) as well as no association (Perzanowski et al., 2006; Gehring et al., 2008) for childhood asthma. Reasons for the paradoxical effects are unclear but could be linked to different presentations of the disease in children with asthma now presenting in allergic and non-allergic forms. Previous studies of endotoxin have shown more consistent associa- tions with allergic sensitization (Gehring et al., 2002, 2007; Tischer et al., 2011). Studies have also shown that exposure to endotoxin is inversely associated with atopic asthma (Braun-Fahrlander et al., 2002; Schram-Bijkerk et al., 2005a) and atopic wheeze (Braun-Fahrlander et al., 2002; Schram-Bijkerk et al., 2005a) among schoolchildren in the general population. However, it is less clear if this relationship also persists among children with asthma since only half of asthma cases in the general population can be attributed to allergic sensitization (Douwes et al., 2002). Furthermore, children with allergic or non-allergic asthma may also demonstrate bronchial hyperressponsiveness (BHR) in response to https://doi.org/10.1016/j.envres.2018.03.012 Received 31 July 2017; Received in revised form 5 March 2018; Accepted 7 March 2018 ⁎ Corresponding author at: Canadian Centre for Health and Safety in Agriculture, University of Saskatchewan, 104 Clinic Place, PO Box 23, Saskatoon, SK, Canada S7N 2Z4. E-mail addresses: olo535@mail.usask.ca (O. Oluwole), donna.rennie@usask.ca (D.C. Rennie), sentil@ulaberta.ca (A. Senthilselvan), roland.dyck@usask.ca (R. Dyck), gaa109@mail.usask.ca (A. Afanasieva), shelly.kirychuk@usask.ca (S. Kirychuk), George.katselis@usask.ca (G. Katselis), josh.lawson@usask.ca (J.A. Lawson). Environmental Research 164 (2018) 302–309 0013-9351/ © 2018 Elsevier Inc. All rights reserved. T