Endotoxin Exposure: Predictors and Prevalence of Associated Asthma Outcomes in the United States

Abstract

Rationale: Inhaled endotoxin induces airway inflammation and is an established risk factor for asthma. The 2005-2006 National Health and Nutrition Examination Survey included measures of endotoxin and allergens in homes as well as specific IgE to inhalant allergens.

Objectives: To understand the relationships between endotoxin exposure, asthma outcomes, and sensitization status for 15 aeroallergens in a nationally representative sample.

Methods: Participants were administered questionnaires in their homes. Reservoir dust was vacuum sampled to generate composite bedding and bedroom floor samples. We analyzed 7,450 National Health and Nutrition Examination Survey dust and quality assurance samples for their endotoxin content using extreme quality assurance measures. Data for 6,963 subjects were available, making this the largest study of endotoxin exposure to date. Log-transformed endotoxin concentrations were analyzed using logistic models and forward stepwise linear regression. Analyses were weighted to provide national prevalence estimates and unbiased variances.

Measurements and main results: Endotoxin exposure was significantly associated with wheeze in the past 12 months, wheeze during exercise, doctor and/or emergency room visits for wheeze, and use of prescription medications for wheeze. Models adjusted for age, sex, race and/or ethnicity, and poverty-to-income ratio and stratified by allergy status showed that these relationships were not dependent upon sensitization status but were worsened among those living in poverty. Significant predictors of higher endotoxin exposures were lower family income; Hispanic ethnicity; participant age; dog(s), cat(s), cockroaches, and/or smoker(s) in the home; and carpeted floors.

Conclusions: In this U.S. nationwide representative sample, higher endotoxin exposure was significantly associated with measures of wheeze, with no observed protective effect regardless of sensitization status.

Keywords: allergy; asthma; house dust; indoor air; wheeze.

Figure 1.

Smoothed plots of prevalence of disease outcomes versus the unweighted, combined bed and bedroom floor dust endotoxin concentration (expressed as endotoxin units per milligram of dust [EU/mg]). (A) The prevalence of wheeze in the past 12 months. (B) The prevalence of doctor-diagnosed asthma. (C) The prevalence of current asthma. (D) The prevalence of the combined outcomes of current asthma and wheeze in the past 12 months. All four plots show a nearly linear increase of the respiratory health outcomes with the endotoxin concentration log values. Solid lines show the smoothed mean prevalence, and dashed lines indicate upper and lower 95% confidence intervals.