Microbial exposure of rural school children, as assessed by levels of N-acetyl-muramic acid in mattress dust, and its association with respiratory health

J Allergy Clin Immunol. 2004 May;113(5):860-7. doi: 10.1016/j.jaci.2004.01.783.


Background: Endotoxin exposure has been shown to be associated with a decreased prevalence of atopic sensitization and symptoms. Yet endotoxin represents only a part of the indoor microbial exposure. Muramic acid, a constituent of peptidoglycan, is present in gram-negative and gram-positive bacteria in the environment and may therefore serve as an additional marker of microbial exposure.

Objective: To study the factors determining the level of indoor exposure to muramic acid/peptidoglycan, as well as its potential association with respiratory health.

Methods: In 553 farm and nonfarm school children from Austria, Switzerland, and Germany, mattress dust muramic acid concentrations were determined, and health was assessed by using IgE measurements and questionnaire information.

Results: The muramic acid concentration was found to be significantly higher in dust from farm children's mattresses than in dust from nonfarm children's mattresses (157 vs 131 ng/mg). Children with higher mattress dust muramic acid concentrations had a significantly lower prevalence of wheezing (odds ratio of highest vs lowest tertile of muramic acid concentration, 0.3; 95% CI, 0.1-0.9), regardless of farming status and endotoxin exposure. The association for asthma was similar, and no association was found with atopic sensitization.

Conclusion: Next to endotoxin, muramic acid provides us with an independent marker of microbial exposure. Unlike endotoxin, muramic acid was inversely associated with wheezing rather than with atopic sensitization.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Asthma / etiology
  • Austria
  • Bedding and Linens / adverse effects*
  • Bedding and Linens / microbiology*
  • Child
  • Dust / analysis
  • Endotoxins / analysis
  • Environmental Microbiology*
  • Germany
  • Humans
  • Immunoglobulin E / blood
  • Muramic Acids / analysis*
  • Rhinitis, Allergic, Seasonal / etiology
  • Rural Health*
  • Switzerland


  • Dust
  • Endotoxins
  • Muramic Acids
  • N-acetylmuramic acid
  • Immunoglobulin E