Our asthma research program involves both exposure assessment and prevention components, and focuses on the relationship between environmental exposures 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. The new component 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. It established a second point-in-time estimate for evaluating allergen and endotoxin exposure trends in U.S. homes, the 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. The NHANES showed that allergens were widespread, but highly variable in U.S. homes. The nations largest indoor allergen study to date demonstrated that more than 90 percent of homes had three or more detectable allergens, and 73 percent had at least one allergen at elevated levels. The presence of pets and pests had a major influence on high levels of indoor allergens, but housing characteristics also mattered; elevated exposure to multiple allergens was more likely in mobile homes, older homes, rental homes, and homes in rural areas. For individual allergens, exposure levels varied greatly with age, sex, race, ethnicity, and socioeconomic status. Differences were also found between geographic locations and climatic conditions. The findings offer beneficial information to a wide audience from allergy and asthma sufferers to clinicians, identifying factors that influence levels of exposure to individual and multiple allergens. Our recent review article summarizes advances in the indoor allergen field and discusses future research needs. Although animal studies have demonstrated that co-exposure to endotoxin and ambient air pollutants may have greater adverse effects on respiratory health than individual exposures, few population-based studies have investigated potential synergistic effects of these pollutants in humans. We linked the NHANES data with the U.S. Environmental Protection Agencys air quality monitoring and modeling data to examine whether co-exposure to residential endotoxin and ambient air pollutants had synergistic effects on asthma related outcomes in the general U.S. population. Our findings demonstrated that co-exposure to elevated levels of endotoxin and fine particulate matter was synergistically associated with recent emergency room (ER) visits for asthma, especially among those who were sensitized to inhalant allergens. In children, co-exposures to elevated levels of endotoxin and higher concentrations of fine particulate matter, as well as nitrogen dioxide, were synergistically associated with recent ER visits for asthma. The results highlight the impact and importance of indoor and outdoor air quality on asthma. Our previous NHANES analyses suggested that overall sensitization to milk, peanut and egg remained constant, but sensitization to shrimp decreased markedly from the late-1980s/early 1990s to the mid-2000s among children. As tropomyosin, the major allergen in shrimp, is found in other arthropods, including cockroaches and dust mites, we investigated whether cockroach and dust mite sensitization might explain the differences observed over time. Shrimp sensitization was found to correlate with cockroach and to a lesser extent with dust mite sensitization. We showed that the decrease in overall and moderate-level shrimp sensitization between the two time periods, 1988-1994 and 2005-2006, was attenuated when adjusting for cockroach sensitization. Our findings strengthen the evidence for the hypothesis that sensitization to shrimp is largely driven by sensitization to other arthropods and depicts changing patterns of sensitization over time in the general U.S. population. In collaboration with several federal agencies and national asthma experts, we developed and implemented a supplemental questionnaire for the National Ambulatory Medical Care Survey (NAMCS), an ongoing nationally representative survey that provides comprehensive information about the provision and use of office- and community health center (CHC)-based medical care services. The one-time supplemental questionnaire in the NAMCS 2012 was designed to assess clinician agreement, self-efficacy and self-reported adherence with the asthma guidelines at the national level. Findings from this study demonstrated notable differences in guideline agreement, adherence, and implementation among asthma care clinicians. To further elucidate factors underlying lower guideline uptake in primary care, we examined variation in guideline implementation among different specialties: family/general medicine, internal medicine, pediatrics, and CHC mid-level care. Across all groups, adherence was higher for history-taking recommendations and lower for recommendations involving patient education, equipment and expertise. Modeling results suggested that, in addition to self-efficacy, pediatric specialty and frequent specialist referral were associated with high guideline adherence. This study will help identify areas and approaches for future research and implementation strategies, including those that are clinician group-specific and those that focus on recommendations that are currently not embraced by the clinician groups. Since the NHANES data set allows for the investigation of many interesting relationships, we continue to study the complex relationships between allergen exposure, allergic sensitization, and disease in more detail. Our research will lead to a better understanding of the characteristics of residential indoor allergen and endotoxin exposures and their role in allergic disorders, 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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