title: A longitudinal analysis of wheezing in young children: the independent effects of early life exposure to house dust endotoxin, allergens, and pets.
abstract: BACKGROUND
  It has been postulated that exposure to bacterial endotoxins and animals early in life might confer protection against the development of asthma and allergies.
  
  
  OBJECTIVE
  We investigated the longitudinal effects of exposure to house dust endotoxin (HDE), allergen levels, and the presence of a dog in the home on wheezing in young children over a 4-year period.
  
  
  METHODS
  Two hundred twenty-six children younger than 5 years were followed for 4 years. Endotoxin and allergen levels were measured from house dust collected at baseline. Longitudinal associations were investigated by using a proportional hazards technique that allowed for multiple outcomes per subject.
  
  
  RESULTS
  Exposure to high concentrations of HDE of greater than the median level was associated with an increased risk for wheezing over the period of observation (multivariate relative risk, 1.52; 95 % CI, 1.07-2.14), but this risk rapidly decreased over time (P for trend =.005). Exposure to cockroach allergen was associated with increased risk for wheezing, whereas exposure to cat allergen and the presence of a dog in the home were both associated with decreased risk for wheezing. The risks associated with cockroach allergen, cat allergen, and dog did not change over the period of observation.
  
  
  CONCLUSIONS
  The negative associations between exposures to dogs and cat allergen and wheeze appear to be independent of the effects of endotoxin and suggest that separate mechanisms might mediate the effects of HDE exposure and pet exposure on the developing immune system.
authors.affiliation: Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Boston, MA, USA.
authors.forename: Augusto A
authors.initials: AA
authors.lastname: Litonjua
authors.forename: Donald K
authors.initials: DK
authors.lastname: Milton
authors.forename: Juan C
authors.initials: JC
authors.lastname: Celedon
authors.forename: Louise
authors.initials: L
authors.lastname: Ryan
authors.forename: Scott T
authors.initials: ST
authors.lastname: Weiss
authors.forename: Diane R
authors.initials: DR
authors.lastname: Gold
mesh_terms: D016902:Air Pollution, Indoor / Q000009:adverse effects*; D000485:Allergens / Q000009:adverse effects*; D000818:Animals; D000829:Animals, Domestic; D001249:Asthma / Q000209:etiology; D002415:Cats; D002675:Child, Preschool; D004285:Dogs; D004391:Dust; D004731:Endotoxins / Q000009:adverse effects*; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D008297:Male; D012135:Respiratory Sounds / Q000209:etiology*; D013997:Time Factors
chemical_list: D000485:Allergens; D004391:Dust; D004731:Endotoxins