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Using the 2003 National Survey of Children's Health sponsored by the federal Maternal and Child Health Bureau, we calculated prevalence estimates of eczema nationally and for each state among a nationally representative sample of 102,353 children 17 years of age and under. Our objective was to determine the national prevalence of eczema/atopic dermatitis in the US pediatric population and to further examine geographic and demographic associations previously reported in other countries. Overall, 10.7% of children were reported to have a diagnosis of eczema in the past 12 months. Prevalence ranged from 8.7 to 18.1% between states and districts, with the highest prevalence reported in many of the East Coast states, as well as in Nevada, Utah, and Idaho. After adjusting for confounders, metropolitan living was found to be a significant factor in predicting a higher disease prevalence with an odds ratio of 1.67 (95% confidence interval of 1.19–2.35, P=0.008). Black race (odds ratio 1.70, P=0.005) and education level in the household greater than high school (odds ratio 1.61, P=0.004) were also significantly associated with a higher prevalence of eczema. The wide range of prevalence suggests that social or environmental factors may influence disease expression.
Abbreviations
AD
atopic dermatitis
ISAAC
International Study of Asthma and Allergies in Childhood
NSCH
National Survey of Children's Health
RUCA
Rural-Urban Commuting Area
SLAITS program
State and Local Area Integrated Telephone Survey
Introduction
Atopic dermatitis (AD) is a global public health concern considering its increasing prevalence and mounting financial costs to health systems (
). The ISAAC (International Study of Asthma and Allergies in Childhood) revealed that AD affects children across the globe, although the disease prevalence varies substantially between countries (
Worldwide time trends in the prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and eczema in childhood: ISAAC phase one and three repeat multicountry cross-sectional surveys.
Worldwide time trends in the prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and eczema in childhood: ISAAC phase one and three repeat multicountry cross-sectional surveys.
Most data regarding AD prevalence in industrialized countries are derived from the study of European populations. Only three previous studies of AD prevalence have reported data from a US population (
Worldwide time trends in the prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and eczema in childhood: ISAAC phase one and three repeat multicountry cross-sectional surveys.
). Further data regarding disease prevalence, geographic variation, and risk factors are required from the United States.
The primary objective of this study was to determine the prevalence of AD in the United States using data obtained from the National Survey of Children's Health (NSCH), a large population-based survey of >100,000 families representing all 50 states. We examined the geographical distribution of the disease and explored whether certain risk factors and associations previously reported in Europe and Asia were also present in the US population.
Results
Univariate analyses
Overall, a total of 9,752 children had a diagnosis of eczema, which translated to a 10.7% national prevalence of eczema in children under 18 years of age. The disease prevalence ranged from 8.7 to 18.1% between states and districts. Figure 1
and Table 1
present state prevalence estimates for US children (0–17 years of age), who were reported to have a diagnosis of eczema in the past 12 months. The highest state prevalence values were reported in many East Coast states, as well as in Utah, Idaho, and Nevada. The lowest state prevalence values were in the middle and southwestern parts of the country (Table 1).
Figure 1Eczema prevalence in the United States shows a trend toward higher disease prevalence in the East Coast states.
Of those children with eczema, 30.7% reported concurrent hay fever and 22.8% reported concurrent asthma consistent with similar AD populations in Europe (
Worldwide time trends in the prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and eczema in childhood: ISAAC phase one and three repeat multicountry cross-sectional surveys.
). As expected, age of the child was a significant determinant of eczema prevalence, given the natural course of the disease (Table 2
). There was a significant effect of the highest reported education level in the household on eczema prevalence, with those households reporting education levels greater than high school having the greatest prevalence of eczema (Table 2). Other significant demographic variables showing positive associations with disease prevalence included living in a metropolitan area (defined using RUCA (Rural-Urban Commuting Area) codes), speaking English as the primary language, and being of Black or multiple race (Table 2).
Table 2Eczema prevalence stratified by primary demographic variables
The birthplace of parents or child was associated with disease prevalence. Children or parents born outside the United States reported a lower prevalence of eczema (Table 3
). A significant association was also found with health insurance status. Children with health insurance had greater eczema prevalence than did those without (10.9 versus 8.2%, P=0.0004), possibly reflecting health-care access disparities.
Table 3Eczema prevalence stratified by birthplace variables
Eczema prevalence showed an association with family structure, with single mothers reporting the highest prevalence (Table 4
). Single child homes had a higher prevalence than did families with more than one child, but birth order did not seem to influence disease prevalence. Children reported to regularly receive child care had a significantly higher prevalence of eczema than did those who did not (Table 5
), with the highest prevalence being seen in those who attended child care outside home. Smoking in the home showed no association with eczema prevalence.
Table 4Eczema prevalence stratified by family structure variables
We developed a logistic regression model to better explain the relationship between area of residency (metropolitan area versus rural area) and eczema prevalence. After adjusting for potential confounders, including race and age of child, parental education level, household income, and health insurance coverage status, metropolitan living continued to be a significant factor in predicting a higher disease prevalence with an odds ratio of 1.67 (95% confidence interval of 1.19–2.35, P=0.008) compared with rural living. Black race (odds ratio 1.70, P=0.005) and education level in the household greater than high school (odds ratio 1.61, P=0.004) were also significantly associated with a higher prevalence of eczema compared with White race and education level less than high school, respectively (Table 6
).
Table 6Subgroup comparisons of variables included in multivariate model
In addition to adjusting for the main effects of potential confounders, interactive effects of insurance coverage, race, and metropolitan residency were included in the final model to better adjust for possible inequities in health-care access. Statistically significant interaction terms included insurance status by metropolitan residency (P=0.047), and the three-way interaction between insurance, race, and residency (P=0.04), suggesting that uninsured and insured, as well as the different racial subgroups, may have experienced differences in health-care access depending on their residency status.
Discussion
Our large population-based study found the prevalence of AD in the United States to be ∼10.7% with a significant variation between states and districts. Urban living and being of Black race were significantly associated with a higher prevalence of eczema after controlling for possible confounders. A general geographic trend toward higher disease prevalence in the East Coast states was also found. We confirmed known demographic AD associations previously observed only in European populations, including the association of AD with higher education levels, higher household incomes, and smaller family sizes. Notable associations not observed in our study included a lack of association with smoking in the household, breast feeding, birth order, gender, or body mass index. The lack of a correlation between body mass index and eczema is supportive of current studies that show no relationship between body mass index and eczema (
Our findings of an AD prevalence of 10.7% in US children 0–17 years of age agree with reported estimates from the three previous US-based studies of AD prevalence. A study by Hanifin reporting the results of a 1998 survey found that 17.1% of the study population had at least one of four eczematous symptoms, whereas 10.7% of respondents reported empirically defined eczema (
reported that of 1,465 Oregon schoolchildren, 5–9 years of age, a prevalence of 11.8% was found based on the question, “Has a doctor ever said that your child has eczema?” Using the self-administered Schultz Larsen questionnaire, a 17.2% lifetime prevalence was found in that study. The global ISAAC study, in which the United States was represented by a sample of 2,422 children from 1 medical center in Seattle, found the prevalence of eczema symptoms to be 8.3% (
). Our study estimate was slightly higher, with a prevalence estimate of 10.7% in the state of Washington.
Similar to the ISAAC study, which revealed striking worldwide geographic variability in AD prevalence, our data revealed significant geographic variability in disease prevalence within the United States with a higher prevalence in the East Coast states. The reason for this variability is not known and is likely multifactorial. One explanation may be the presence of a higher number of metropolitan centers in the Eastern versus Western United States. Our data revealed a higher eczema prevalence rate in metropolitan areas even when controlling for confounders. Several previous studies of atopic disease have reported a similar increase in disease prevalence in metropolitan/urban areas compared with rural areas (
Worldwide time trends in the prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and eczema in childhood: ISAAC phase one and three repeat multicountry cross-sectional surveys.
). For example, an increased prevalence of allergic disease in Ethiopia was associated with the use of modern fuels, particularly kerosene use in homes (when compared with other biomass fuel) (
was the heavy exposure to microorganisms in soil and vegetation when living in rural farming areas. Cultural and behavioral factors that affect the skin barrier may also have a role.
found a correlation between an increased hygiene score (that included the frequency of washing/wiping hands and faces and bathing practices of young children) and subsequent eczema risk. Whether skin care practices vary between rural and metropolitan inhabitants is not known.
An unexpected association in our study was the greater prevalence of eczema in Black and multirace populations compared with Whites. Hanifin did not find statistically significant differences between various race populations and their prevalence of eczema. A few previous studies have reported racial disparities in eczema prevalence (
found a higher prevalence of AD in Black Caribbean individuals in London compared with Whites. Using medical care usage as a proxy for disease prevalence,
reported an increased use of medical care for AD by Blacks and Asian/Pacific Islanders when compared with Whites. It is not known whether these racial differences derive from environmental or genetic influences. There are no large studies of the prevalence of common filaggrin mutations in an African population. Studies in asthma have also reported similar racial disparities and differences in socioeconomic status and air quality have been proposed as the possible explanations (
A significant limitation of our study was that we could not be certain whether geographic differences in disease prevalence reflected differences in access to medical care or dermatological specialty care. There are fewer dermatologists per capita in rural areas compared with urban areas, although wait time to be seen by a dermatologist was not statistically different between urban and rural areas (
). Our regression model controlled for this issue, but this does not eliminate the potential bias completely. Another limitation of this study was the nature of the self-reported survey data collection. Diagnoses were not confirmed by a chart review or direct examination of the patients. Single questions addressing parent recall of physician-diagnosed eczema that have been validated and used in other prevalence studies reported a high concordance between using a similar single question (“Has a doctor ever said that your child has eczema?”) with direct clinical examination and questionnaire diagnosis of AD (
). Another study from Germany tested the validity of the diagnosis of AD using the question, “Has a physician ever diagnosed eczema in your child?” It showed 63% sensitivity and 88% specificity using dermatological exam as the gold standard (
). On the basis of the results of these studies, the wording of the question in this survey has adequate sensitivity and specificity to provide meaningful data on eczema prevalence. Finally, these survey data are now 7 years old.
Materials and Methods
Data source
We used data obtained from the 2003 NSCH survey of 102,353 households, which was designed to estimate the prevalence of various child health issues, including physical, emotional, and behavioral factors. The NSCH was sponsored by the Maternal and Child Health Bureau and the US Department of Health and Human Services. The National Center for Health Statistics conducted a total of 102,353 interviews using the SLAITS (State and Local Area Integrated Telephone Survey) program. The telephone numbers were chosen at random, followed by identification of the households with one or more children under the age of 18 years. Subsequently, one child was randomly selected for interview. The survey results were weighted to represent the population of noninstitutionalized children nationally and in each state. Using data obtained from the US Bureau of the Census, weights were adjusted for age, sex, race, ethnicity, household size, and educational attainment of the most educated household member to provide a data set that was more representative of each state's population of noninstitutionalized children <18 years of age. The National Center for Health Statistics of Center for Diseases Control and Prevention oversaw sampling and telephone interviews. More detailed information on the survey has been previously published (
We calculated the period prevalence of AD/eczema using the NSCH question, “During the past 12 months, have you been told by a doctor or other health professional that (child's name) had eczema or any kind of skin allergy?”
To limit the effect health-care access may have on the results, we excluded all subjects who responded “no” to the question, “During the past 12 months, did (child) see a doctor, nurse, or other health care professional for any kind of medical care, including sick-child care, well-child check-ups, physical exams, and hospitalizations?” We also included health-care insurance status in our final regression model when we examined the role of metropolitan living on AD prevalence.
NSCH data were interpreted to calculate the national prevalence of eczema for the United States and for each state. Further investigation into the influences of race, geography, socioeconomic status, education levels, family size, place of residence, and birth order was performed based on previously described associations in the literature found in European populations (
Analyses were performed using SURVEY procedures in SAS version 9.2 (SAS, Cary, NC, USA). Univariate associations were tested by the Rao–Scott χ2 method. Multivariate results were obtained by logistic regression for domains of weighted survey data. Regression analysis did not include data from many states (including Alaska, Connecticut, Delaware, Hawaii, Idaho, Maine, Maryland, Massachusetts, Montana, Nevada, New Hampshire, North Dakota, Rhode Island, South Dakota, Vermont, and Wyoming) for which metropolitan residency status was unavailable. The regression model used residency status (metropolitan versus rural) to predict diagnosis of pediatric eczema while controlling for potential demographic confounders, including race and age and health insurance coverage status. The number of children living in the home was not significantly associated with eczema diagnosis; therefore, this variable was removed to simplify the model. Interactive effects between race, insurance status, and metropolitan residency were included in an attempt to better control for inequity in health-care access between races and areas of residency. Odds ratios for specific demographic comparisons were determined using the final multivariate model, and their P-values were adjusted for multiple comparisons using the false discovery rate method (Table 6).
ACKNOWLEDGMENTS
We thank the Child and Adolescent Health Measurement Initiative (CAHMI) at the Oregon Health and Science University for providing the data set (http://www.cahmi.org). This publication was made possible with support from the Oregon Clinical and Translational Research Institute (OCTRI), grant number UL1 RR024140 from the National Center for Research Resources (NCRR), a component of the National Institutes of Health (NIH), and NIH Roadmap for Medical Research. We also thank Christine E. Carocci for assistance with proofreading, editing, and preparation of this paper. This work was performed in Portland, Oregon, USA.
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Worldwide time trends in the prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and eczema in childhood: ISAAC phase one and three repeat multicountry cross-sectional surveys.
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