Our asthma research program involves both exposure assessment and prevention components, and focuses on the relationship between exposure to common indoor allergens and asthma prevalence and morbidity. We have worked with investigators at the CDC/NCHS to implement the allergen and asthma component of NHANES 2005-2006. We collected bedroom dust, measured total and allergen-specific IgE and assessed asthma and allergy prevalence and morbidity in approximately 9000 individuals in the U.S. Analysis of this large dataset 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 including asthma. In analysis of IgE levels to estimate nationwide prevalence of allergic sensitization, median total IgE values were found to be higher for males than for females;for non-Hispanic Blacks and Mexican-Americans than for non-Hispanic whites;for those with less than a 12th grade education, increased poverty, higher serum cotinine levels, and higher body mass indices;and for those with at least 1 positive specific IgE result. Current asthma was reported by 8.8% of the population. The prevalence of asthma differed significantly by age, race/ethnicity, sex, poverty, serum cotinine level, and body size. The prevalence of asthma was higher among allergic than non-allergic individuals. The geometric mean for total IgE level was significantly higher among asthmatics than non-asthmatics. Among the US population 6 years and older, total serum IgE levels were associated with doctor-diagnosed current asthma but only among persons who had allergies. There are also differences between racial groups in the relationship between serum cholesterol and allergy in the US population with non-Hispanic blacks having a reduced odds of allergy with increasing levels of non-HDL Cholesterol. This relationship was not significant in any other racial group (i.e., non-Hispanic whites and Mexican Americans). When considering asthma, Total Cholesterol and non-HDL Cholesterol were lower in those with current asthma than in those without current asthma;however this relationship is primarily seen in Mexican Americans and not in non-Hispanic groups. Among participants 6 years and older, prevalence of diagnosed hay fever was 11.3%, and 6.6% reported current hay fever. One-third of the participants (33.9%) had diagnosed allergies, and 23.5% suffered from current allergies. The reported symptoms, with or without diagnosis of allergy, were most consistently associated with plant-, pet-, and mold-specific IgEs. The greatest increase in odds was observed for hay fever and plant specific IgEs;however, sensitization to dust mites, which is highly prevalent in the population, was not independently associated with these outcomes. Although levels of total IgE may overlap between nonatopic and atopic individuals, increase in total IgE appeared to have a small, but independent effect on allergy-related outcomes. We also explored the complex relationships between obesity, serum IgE levels, and allergy and asthma outcomes. Because C-reactive protein (CRP), a marker of systemic inflammation, has been associated with asthma, we also investigated CRPs potential role in these relationships. The analysis showed that overweight status in children (aged 2-19 years) was associated with allergic sensitization in the NHANES 2005- 2006;interestingly, the association was driven largely by allergic sensitization to foods. The data suggested that systemic inflammation might play role in the development of allergic disease;CRP levels in children were positively correlated with total IgE levels, and the relationship was confounded by BMI. To investigate associations in relation to asthma, we included children ages 2-19 (N=16,074) from the 1999-2006 NHANES. The results showed that being overweight or obese was associated with an increased likelihood of current asthma. The association with BMI was uniformly stronger for individuals in the obese category than for overweight subjects. Interestingly, the relationship between continuous BMI and asthma was stronger among non-atopic subjects than among atopic individuals. Our findings are consistent with studies in adults that have shown obesity to be more strongly related to nonatopic than atopic asthma. Increased CRP levels were associated with current asthma in non-atopic children, but not in atopic children. This association, however, was confounded by BMI which suggests that being overweight may lead to systemic inflammation that in turn leads to an increased risk of non-atopic asthma. In large scale studies laboratory testing for allergic sensitization is not always feasible. Therefore, standard written questionnaires have been the principal instrument for measuring atopic disease and symptom prevalence;however, relying only on self-reported data may introduce bias. The relationship between various clinical measures of atopy (e.g. skin prick test positivity, elevated total or specific IgE) and questionnaire information has been assessed in a number of studies, none have been conducted in a large, nationally representative population in the U.S. To evaluate the predictive value of questionnaires to assess atopy, we used data from the NHANES 2005-2006. We focused on five potentially allergic conditions (hay fever, allergy, eczema, itchy rash, and rhinitis) and recent symptoms. For hay fever, allergy, and eczema, the question required a doctor-diagnosis to be considered positive. Given that it was unlikely any single questionnaire item could capture all atopic individuals, we generated combinations of variables and assessed their ability to predict atopy. Questionnaire responses were assessed for sensitivity, specificity, and positive and negative predictive values for atopy. Of the NHANES 2005-2006 participants who had specific IgE data available (N=8,334), 44% were atopic ( 1 positive specific IgE) and 53% reported one or more allergic conditions. Discordance between atopy and allergic conditions was considerable;37% of atopics reported no allergic condition and 48% who reported an allergic condition were not atopic. Therefore, no combination of self-reported allergic conditions resulted in both high sensitivity and high specificity for IgE. The positive predictive value of reported allergic conditions for atopy ranged from 50% for eczema to 72% for hay fever, while the negative predictive value ranged from 57% for eczema to 65% for any condition. Although questionnaires are often the best, and sometimes the only way to collect medical information on a large sample, their limitations need to be taken into account.
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