Our asthma research program involves both exposure assessment and prevention components, and focuses on the relationship between exposure to indoor allergens and asthma prevalence and morbidity. In collaboration with investigators at the CDC/NCHS, we developed and implemented an allergy/asthma focused component for the National Health and Nutrition Examination Survey (NHANES). This component, included in NHANES 2005-2006, queried on allergy and asthma prevalence and morbidity, measured levels of common indoor allergens and endotoxin in bedroom dust, and quantified total and allergen-specific IgE levels in serum of more than 9000 participants. Analysis of this large data set will allow us to 1) estimate nationwide prevalence of indoor allergen and endotoxin exposures, 2) estimate nationwide prevalence of allergic sensitization to indoor, outdoor and food allergens, 3) estimate nationwide prevalence of allergic diseases, including asthma, and 4) investigate the complex relationships between allergen and endotoxin exposures, allergic sensitization and allergic diseases. NHANES 2005-2006 not only tested a greater number of allergens across a wider age range than prior studies, but also provided quantitative information on the extent of allergic sensitization and exposures to indoor allergens and endotoxin. The NHANES 2005-2006 data demonstrated that endotoxin levels were positively associated with asthma-related outcomes, especially wheezing. The relationships of endotoxin with wheeze did not exhibit a threshold effect but did show a positive dose-response association over the range of values. Poverty and presence of children, pets, cockroaches, carpeting, and/or smokers were consistently associated with higher endotoxin levels in the home. Using data from NHANES, we determined whether sensitization to common food allergens increased in U.S. children from 1988-1994 to 2005-2006 and whether these trends differed by race and/or ethnicity. In contrast with a body of literature showing increased prevalence of self-reported food allergy and increased health care utilization for its manifestations, NHANES data (NHANES III, NHANES 2005-2006) suggested that sensitization to milk, peanut, and egg, as measured by food-specific IgE, remained constant, while sensitization to shrimp decreased among children aged 6-19 years. On the other hand, we observed a trend toward increased prevalence of moderate- and high-level sensitization to the combination of milk, egg, and peanut among non-Hispanic blacks but not among other racial/ethnic groups. Our findings might reflect either changes in the relationship between sensitization and clinical allergy or changes in the recognition and diagnosis of food allergy. In a randomized, controlled intervention study, we investigated whether education coupled with commercially available in-home test kits, which provide semi-quantitative information on residential allergen levels, influenced compliance with recommended dust mite reduction strategies. Our results suggested that parents might become more motivated to participate in allergen reduction interventions when they could actually see results for themselves. In households that received the test kits, dust mite allergen levels were significantly reduced over time compared to control homes. This is the first study to demonstrate that the use of in-home test kits along with education may beneficially influence behaviors and attitudes towards dust mite reduction strategies and can help to reduce dust mite allergen levels in the home. We also used NHANES data from the survey cycles 1999 to 2004 to investigate exposure to individual environmental chemicals and selected mixtures in relation to the presence of antinuclear antibodies (ANA), a widely used biomarker of autoimmunity. This study showed several associations between chemical concentration and ANA positivity, but only the association in males exposed to triclosan remained statistically significant. Thus, background levels of most xenobiotic exposures typical in the U.S. population are not strongly associated with ANA. Since the NHANES data set allows for the investigation of many interesting relationships, we continue to investigate the complex relationships between allergen exposure, allergic sensitization, and disease in more detail. In addition to providing data on these relationships, the NHANES 2005-2006 will establish a second point-in-time estimate for evaluating allergen and endotoxin exposure trends in U.S. homes, first being established in the National Survey of Lead and Allergens in Housing, which we completed in collaboration with the Department of Housing and Urban Development. Our research will lead to a better understanding of the characteristics and predictors of residential indoor allergen and endotoxin exposures, which in turn provides insights into development of effective environmental intervention approaches for the management of allergic diseases such as asthma.
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