Published ahead of print on September 1, 2005, doi:10.1164/rccm.200505-758OC
Am. J. Respir. Crit. Care Med., Volume 172, Number 11, December 2005, 1371-1377
A more recent version of this article appeared on December 1, 2005
Submitted on May 13, 2005
Accepted on September 1, 2005
Endotoxin Exposure is a Risk Factor for Asthma: The National Survey of Endotoxin in U.S. Housing
Peter S Thorne1*, Katarina Kulhankova1, Ming Yin2, Richard Cohn2, Samuel J Arbes, Jr.3, and Darryl C Zeldin3
1 Environmental Health Sciences Research Center, The University of Iowa, Iowa City, IA, USA,
2 Constella Group Inc., Durham, NC, USA,
3 Division of Intramural Research, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA
* To whom correspondence should be addressed. E-mail: peter-thorne{at}uiowa.edu.
Background: While research has shown that early life exposure to household endotoxin protects against development of allergies, studies are less clear on the relationship between household endotoxin exposure and prevalence of wheezing and asthma. We assayed 2552 house dust samples in a representative nationwide sample to explore relationships between endotoxin exposures and risk factors for asthma, asthma symptoms and medication use.
Methods: House dust was vacuum-sampled from five locations within homes and assayed for endotoxin. Health, demographic and housing information was assessed through questionnaire and on-site evaluation of 2456 residents of 831 homes selected to represent the demographics of the U.S.
Results: Endotoxin concentration (EU/mg) and load (EU/m2) were highly correlated (r=0.73-0.79). Geometric mean endotoxin concentrations were (in EU/mg): bedroom floors: 35.3 (5th-95thpercentile: 5.0-260); bedding: 18.7 (2.0-142); family room floors: 63.9 (11.5-331); sofas: 44.8 (6.4-240); kitchen floors: 80.5 (9.8-512). Multivariate analysis demonstrated significant relationships between increasing endotoxin levels and diagnosed asthma, asthma symptoms in the past year, current use of asthma medications, and wheezing among residents of the homes. These relationships were strongest for bedroom floor and bedding dust and were observed in adults only. Modeling the joint effect of bedding and bedroom floor endotoxin on recent asthma symptoms yielded an adjusted odds ratio of 2.83 (95%CI: 1.01-7.87). When stratified by allergy status, allergic subjects with higher endotoxin exposure were no more likely to have diagnosed asthma or asthma symptoms than non-allergic subjects.
Conclusion: This study demonstrates that household endotoxin exposure is a significant risk factor for increased asthma prevalence.
Key words: Wheeze, Airways Inflammation, House Dust, Lipopolysaccharide, Hygiene Hypothesis
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