title: Endotoxin as a determinant of asthma and wheeze among rural dwelling children and adolescents: a case-control study.
abstract: BACKGROUND
  The association between endotoxin exposure and asthma is complex and has been associated with rural living. We examined the relationship between domestic endotoxin and asthma or wheeze among rural school-aged children (6-18 years) and assessed the interaction between endotoxin and other characteristics with these outcomes.
  
  
  METHODS
  Between 2005 and 2007 we conducted a case-control study of children 6-18 years in the rural region of Humboldt, Canada. Cases (n = 102) reported doctor-diagnosed asthma or wheeze in the past year. Controls (n = 208) were randomly selected from children without asthma or wheeze. Data were collected to ascertain symptoms, asthma history and indoor environmental exposures (questionnaire), endotoxin (dust collection from the play area floor and child's mattress), and tobacco smoke exposure (saliva collection). Statistical testing was completed using multiple logistic regression to account for potential confounders and to assess interaction between risk factors. A stratified analysis was also completed to examine the effect of personal history of allergy.
  
  
  RESULTS
  Among children aged 6-12 years, mattress endotoxin concentration (EU/mg) and load (EU/m2) were inversely associated with being a case [odds ratio (OR) = 0.44, 95% confidence interval (CI) = 0.20-0.98; and OR = 0.38, 95% CI = 0.20-0.75, respectively]. These associations were not observed in older children or with play area endotoxin.
  
  
  CONCLUSIONS
  Our results suggest that endotoxin exposure might be protective for asthma or wheeze. The protective effect is found in younger school-aged, non-allergic children. These results may help explain the inconsistencies in previous studies and suggest that the protective effects of endotoxin in the prevention of atopy and asthma or wheeze are most effective earlier in life.
authors.affiliation: Canadian Centre for Health and Safety in Agriculture & Department of Medicine, University of Saskatchewan, Saskatoon, SK, Canada. josh.lawson@usask.ca
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Lawson
authors.forename: James A
authors.initials: JA
authors.lastname: Dosman
authors.forename: Donna C
authors.initials: DC
authors.lastname: Rennie
authors.forename: Jeremy R
authors.initials: JR
authors.lastname: Beach
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Newman
authors.forename: Trever
authors.initials: T
authors.lastname: Crowe
authors.forename: Ambikaipakan
authors.initials: A
authors.lastname: Senthilselvan
mesh_terms: D000293:Adolescent; D001249:Asthma / Q000276:immunology*; D002170:Canada / Q000453:epidemiology; D016022:Case-Control Studies; D002648:Child; D004731:Endotoxins / Q000276:immunology*; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D008297:Male; D012135:Respiratory Sounds / Q000276:immunology*; D012307:Risk Factors; D012424:Rural Population; D011795:Surveys and Questionnaires
chemical_list: D004731:Endotoxins