Self-Reported Asthma in Adults and Proxy-Reported Asthma in Children -- Washington, 1997-1998

Increased awareness of asthma as a public health problem reflects recent increases in asthma prevalence, asthma-related visits to hospital emergency departments, and asthma-related mortality (1). To assess the prevalence of asthma in Washington, the Washington State Department of Health added survey items on asthma to its 1997 and 1998 Behavioral Risk Factor Surveillance System (BRFSS) survey. This report summarizes the results of those surveys, which indicate that persons with asthma reported significantly lower health status than other respondents and that a substantial proportion of households with children reported having a child with asthma.

BRFSS is a state-based, random-digit-dialed survey of the noninstitutionalized population aged greater than or equal to 18 years; the survey collects information about modifiable risk factors for chronic diseases and other leading causes of death. CDC and state and territorial departments of health use the system to measure achievement toward both national and state health objectives.

BRFSS respondents were asked "Has a doctor or other health care professional ever told you that you have asthma?" and "How old were you the first time this happened?" These questions were followed by "Has a doctor ever said that one of the children currently living in your household has asthma?" and, if yes, "How old is this child (are these children)?"

The number of respondents was 3604 both in 1997 and 1998. To improve the precision of estimates, data from the two survey years were combined. Except for the estimated number of children with asthma in the population, prevalence estimates and 95% confidence intervals (CIs) were calculated using weighted data to adjust for sample design. The number of children with asthma was stratified by age and its 95% CI was calculated on pooled unweighted data.

Among adults, 10.8% reported having had asthma at some point in their life (i.e., ever asthma), and the median age at onset was 19 years (range: 1-81 years). Persons with asthma reported significantly lower health status than other respondents: 18.8% (95% CI=15.8%-21.8%) reported fair or poor health, compared with 9.9% (95% CI=9.1%-10.7%) of those not reporting asthma. The number of adults with asthma in Washington was an estimated 450,000 (95% CI=413,000-479,000).

At least one child aged less than or equal to 17 years was reported to reside in 39.4% of households. Of those households with children, 15.9% (95% CI=14.2%-17.6%) had a child with asthma. Overall, 10.1% of children ever had asthma: 7.8% of those aged less than 5 years, 9.5% of those aged 5-12 years, and 12.8% of those aged 13-17 years. The number of children with asthma was an estimated 151,000 (95% CI=139,000-165,000).

For children with asthma, results varied by socioeconomic status, family history, and whether the respondent was a current smoker. Compared with households with an annual income greater than $20,000, poorer households had higher asthma prevalence, with a rate ratio of 1.9 among children aged less than 5 years. When the respondent self-reported asthma, the prevalence of asthma in household children was 34% (p less than 0.001), compared with 14% when the respondent did not report asthma. In those households in which the respondent reported being a current smoker, 20.0% contained a child with asthma compared with 14.9% (p=0.04) of other households.

Reported by: SC Macdonald, PhD, LS Bensley, PhD, J VanEenwyk, PhD, Acting State Epidemiologist, Office of Epidemiology; K Wynkoop Simmons, PhD, Washington State Dept of Health. Air Pollution and Respiratory Health Br, Div of Environmental Hazards and Health Effects, National Center for Environmental Health, CDC.

Editorial Note:

Multiple factors affect the risk for asthma and the development for subsequent morbidity and mortality. The public health approach to asthma requires a multidisciplinary solution that includes environmental health issues such as outdoor air pollution (industrial and domestic [such as wood smoke]), indoor air quality (environmental tobacco smoke and allergens), and community health education for parents, day care centers and schools; occupational health programs to address workplace asthma (2); and health services delivery to ensure quality of care (biomedical and psychosocial) and access to adequate ambulatory primary care. In 1997, six states reported using various sources of data for public health surveillance of asthma: hospitalization data (four states), mortality data (four states), BRFSS (two states), and clinician reporting (one state) (3).

As public health surveillance systems evolve from those focused primarily on infectious diseases to systems focused on the full range of public health problems, new surveillance methods are being developed and adopted (4,5). Surveillance programs for asthma face challenges in developing diverse systems to address these various information needs (6,7). BRFSS is large, flexible, and yields data that can be compared across states and can be used to measure trends over time.

CDC developed a two-item BRFSS module on asthma for 1999, consistent with the standard 1998 surveillance case definition for asthma (8). This module is in use in 14 states, Puerto Rico, and Washington, DC. The items ask "Did a doctor ever tell you that you had asthma?" and "Do you still have asthma?" Previously, states have included asthma items as state-added questions (3).

The findings in this report are subject to at least four limitations. First, the BRFSS telephone survey method excludes non-English speakers and households without telephones; these households may have different rates of asthma. Second, reporting of asthma in children by proxy may be imperfect; the respondent is not necessarily the parent, and, even if a parent, may be the less knowledgeable parent. However, because of the dramatic symptoms of asthma, most persons are aware of the condition in the household. Third, the statewide prevalence data from BRFSS need to be supplemented by local survey data to optimize targeting of programs for asthma prevention and control. Finally, Washington measured "ever asthma" rather than "current asthma," as is done by the CDC module. However, the higher prevalence of fair or poor health in adults reporting "ever asthma" indicates that asthma persists for many of these persons. In addition, for the youngest children, "ever asthma" and "current asthma" are probably similar.

The prevalences reported for Washington are somewhat higher than national data previously reported from the National Health Interview Survey (NHIS) in 1998 (1). During 1993-1994, NHIS data showed an estimated average annual rate of self-reported asthma during the preceding 12 months ranging from 4.5% in older adults to 5.8% in children aged 0-4 years and 7.4% in children aged 5-14 years. The prevalences reported for Washington are somewhat higher than those forecast for the state using synthetic estimation methods based on NHIS data (9). The differences in estimates may be a result of increasing prevalence over time, differences between survey methods, and higher incidence or greater duration in Washington. The differences do not result from racial distribution: blacks, who have higher rates of asthma in NHIS data, are underrepresented in Washington, accounting for 3.1% of the population in 1990, compared with 12% nationally.

Washington has adopted the CDC module for its 1999 BRFSS and has modified its child asthma items to ask about "current asthma." The module is available on the World-Wide Web at http://www.doh.wa.gov/EHSPHL/Epidemiology/NICE.* Use of these types of surveys to ascertain the prevalence of asthma is an important component in the public health approach to asthma. To facilitate pooling and comparing data across states and regions, states should consider using uniform or comparable questions.

References

1. CDC. Surveillance for asthma--United States, 1960-1995. MMWR 1998;47(no. SS-1).
2. CDC. Surveillance of work-related asthma in selected U.S. states using surveillance guidelines for state health departments--California, Massachusetts, Michigan, and New Jersey, 1993-95. MMWR 1999;48(no. SS-3):1-20.
3. CDC. Monitoring environmental disease--United States, 1997. MMWR 1998;47:522-5.
4. Berkelman RL, Stroup DF, Buehler JW. Public health surveillance. In: Detels R, Holland WW, McEwan J, Omenn GS, eds. Oxford textbook of public health. 3rd ed. New York, New York: Oxford University Press, 1997:735-50.
5. Meriwether RA. Blueprint for a national public health surveillance system for the 21st century. J Public Health Management Practice 1996;2:16-23.
6. Thacker SB, Stroup DF, Parrish RG, Anderson HA. Surveillance in environmental public health: issues, systems, and sources. Am J Public Health 1996;86:633-8.
7. Macdonald SC, Pertowski CA, Jackson RJ. Environmental public health surveillance. J Public Health Management Practice 1996;2:45-9.
8. Council of State and Territorial Epidemiologists. Asthma surveillance case definition: position statement adopted at 1998 CSTE annual meeting, Des Moines, Iowa.
9. CDC. Forecasted state-specific estimates of self-reported asthma prevalence--United States, 1998. MMWR 1998;47:1022-5.

* References to sites of non-CDC organizations on the Internet are provided as a service to MMWR readers and do not constitute or imply endorsement of these organizations or their programs by CDC or the U.S. Department of Health and Human Services. CDC is not responsible for the content of pages found at these sites.

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