title: Does early indoor microbial exposure reduce the risk of asthma? The Prevention and Incidence of Asthma and Mite Allergy birth cohort study.
abstract: BACKGROUND
  Exposure to microbial agents might inhibit the development of atopy and asthma.
  
  
  OBJECTIVE
  We measured the association between microbial exposure assessed at 3 months and the development of atopic sensitization and doctor-diagnosed (DD) asthma and wheeze in the first 4 years in a birth cohort study of children with atopic mothers.
  
  
  METHODS
  Endotoxin, fungal (1-->3)-beta-D-glucans, extracellular polysaccharides from the genera Penicillium and Aspergillus (EPS-Pen/Asp), and dust on living room floors were measured at 3 months of age. Serum IgE levels against common allergens were determined at 1 and 4 years, and questionnaire information about respiratory morbidity was collected yearly.
  
  
  RESULTS
  Microbial levels in mattresses were low and not associated with serum IgE levels, DD asthma, and wheeze. Floor levels of biocontaminants and dust, on the other hand, were inversely associated with DD asthma, being most pronounced for endotoxin (odds ratio [OR], 0.40; 95% CI, 0.21-0.77) and EPS-Pen/Asp (OR, 0.42; 95% CI, 0.18-0.99). Mutual adjustment for other exposures did not significantly alter the results for endotoxin and only moderately affected the results for EPS-Pen/Asp. Persistent wheeze was also consistently less common in the high-exposure group, being significant only for EPS-Pen/Asp (OR, 0.37; 95% CI, 0.15-0.96). Transient wheeze and wheeze in the past 12 months were also reduced, but effects were smaller and not significant. Relationships with serum-specific IgE levels, which could only be assessed in 41% at age 4 years, were less pronounced and statistically significant only for EPS-Pen/Asp.
  
  
  CONCLUSIONS
  Early exposure to common microbial contaminants, including fungal agents, might protect against asthma.
  
  
  CONCLUSIONS
  Microbial exposure in early life might protect against asthma and might constitute a novel target for prevention.
authors: Institute for Risk Assessment Sciences (IRAS), Utrecht University, Amsterdam.
authors: Jeroen
authors: J
authors: Douwes
authors: Rob
authors: R
authors: van Strien
authors: Gert
authors: G
authors: Doekes
authors: Jet
authors: J
authors: Smit
authors: Marjan
authors: M
authors: Kerkhof
authors: Jorrit
authors: J
authors: Gerritsen
authors: Dirkje
authors: D
authors: Postma
authors: Johan
authors: J
authors: de Jongste
authors: Noemie
authors: N
authors: Travier
authors: Bert
authors: B
authors: Brunekreef