Current Asthma Prevalence --- United States, 2006--2008

Jeanne E. Moorman, MS1

Hatice Zahran, MD1

Benedict I. Truman, MD2

Michael T. Molla, PhD3

1National Center for Environmental Health, CDC

2Epidemiology and Analysis Program Office, CDC

3National Center for Health Statistics, CDC

Corresponding author: Jeanne Moorman, MS, Division of Environmental Hazards and Health Effects, National Center for Environmental Health, CDC, 4770 Buford Highway, MS F-58, Atlanta GA 30341. Telephone: 770-488-3726; Fax: 770-488-1540; E-mail: zva9@cdc.gov.

Asthma is a chronic inflammatory disorder of the airways characterized by episodic and reversible airflow obstruction, airway hyper-responsiveness, and underlying inflammation. Common asthma symptoms include wheezing, coughing, and shortness of breath (1). With correct treatment and avoidance of exposure to environmental allergens and irritants that are known to exacerbate asthma, the majority of persons who have asthma can expect optimal symptom control (2).

Multiple reports provide detailed surveillance information on asthma (1,3--6). A 1987 report that included asthma surveillance data for 1965--1984 identified differences among certain demographic groups by age, sex, and race/ethnicity (3). Subsequent asthma surveillance reports confirmed these differences and documented that the differences have persisted over time (1,4). These reports indicate that population-based asthma prevalence rates, emergency department visit rates, and hospitalization rates were higher among blacks than among whites, higher among females than among males, higher among children than among adults, and higher among males aged 0--17 years than among females in the same age group. In addition, more detailed analysis of ethnicity data demonstrated that different Hispanic groups had differing health outcomes. Among Hispanics, those of Puerto Rican descent (origin or ancestry) had higher asthma prevalence and death rates than other Hispanics (e.g., those of Mexican descent), non-Hispanic blacks, and non-Hispanic whites (5,6).

To examine whether disparities in asthma prevalence exist among certain demographic groups, CDC analyzed data from the National Health Interview Survey (NHIS) for 2006--2008. NHIS is an annual, in-person survey of the civilian, noninstitutionalized U.S. population based on a multistage sampling of households (7). An adult family member is selected to act as a proxy respondent for children. NHIS routinely includes two questions that are used to estimate national asthma prevalence. The question, "Have you ever been told by a doctor or other health professional that you had asthma?" has been used as a lifetime prevalence measure for asthma since 1997. A second question, "Do you still have asthma?" was added in 2001 to assess current asthma prevalence. Consistent with previous CDC publications, respondents were considered to have current asthma if they answered "yes" to both questions (1,4). Race/ethnicity was categorized on the basis of the respondents' self-reported classification. Results for four racial/ethnic groups are reported: non-Hispanic white, non-Hispanic black, multiracial, and Hispanic of Puerto Rican descent. Current asthma prevalence also was estimated by sex (males and females), age group (children aged 0--17 years and adults aged ≥18 years), and federal poverty level. Analyses of disparities in disability status, education, geographic region, and other racial/ethnic populations were not included because of low prevalence or limitations due to data quality or manuscript length. Three years of survey data were combined to provide more stable estimates for relatively small groups. Analysis software accounted for complex sample design, and sample weights were used to produce national estimates. Estimates were age-adjusted by using the year 2000 age distribution, except those for children. Comparative terms used in this report (e.g., "higher" and "similar") indicate the results of statistical testing at p<0.05.

During 2006--2008, an estimated 7.8% of the U.S. population had current asthma (Table). Current asthma prevalence was higher among the multiracial (14.8%), Puerto Rican Hispanics (14.2%), and non-Hispanic blacks (9.5%) than among non-Hispanic whites (7.8%). Current asthma prevalence also was higher among children (9.3%) than among adults (7.3%), among females (8.6%) than among males (6.9%), and among the poor (11.2%) than among the near-poor (8.4%) and nonpoor (7.0%).*

When examined within the three federal poverty levels, prevalence by race/ethnicity was different than when race/ethnicity was examined alone. Among the poor, non-Hispanic whites and non-Hispanic blacks had similar prevalence (12.5% and 12.2%, respectively). In contrast, Puerto Rican Hispanics and the multiracial also had similar but substantially higher prevalence (22.4% and 20.5%, respectively). Among the near-poor, non-Hispanic blacks and non-Hispanic whites had similar prevalence (9.7% and 9.2%, respectively), and Puerto Rican Hispanics and the multiracial also had similar prevalence (14.9% and 13.6%, respectively). Among the nonpoor, non-Hispanic blacks had higher prevalence than non-Hispanic whites (8.4% and 7.0%, respectively). In contrast, the multiracial and Puerto Rican Hispanics had similar prevalence (13.4% and 10.4%, respectively).

For children (9.3% prevalence), current asthma prevalence was higher among Puerto Rican Hispanics (18.4%), non-Hispanic blacks (14.6%), and the multiracial (13.6%) than among non-Hispanic whites (8.2%). Asthma prevalence was higher among males (10.7%) than among females (7.8%). Among poor children, Puerto Rican children, multiracial children, and non-Hispanic black children had higher asthma prevalence (23.3%, 21.1%, and 15.8%, respectively) than poor non-Hispanic white children (10.1%) (Table).

For adults (7.3% prevalence), current asthma prevalence was higher among the multiracial (15.1%) and Puerto Rican Hispanics (12.8%) than among non-Hispanic blacks (7.8%) and non-Hispanic whites (7.7%). Asthma prevalence was higher among women (8.9%) than among men (5.5%). Among poor adults, Puerto Rican adults and multiracial adults had higher asthma prevalence (22.1% and 20.2%, respectively) than poor non-Hispanic black adults (10.9%) (Table).

For females of all ages (8.6% prevalence), current asthma prevalence was higher among the multiracial (17.4%), Puerto Rican Hispanics (16.9%), and non-Hispanic blacks (10.3%) than among non-Hispanic whites (8.7%). For males of all ages (6.9% prevalence), current asthma prevalence was higher among the multiracial (12.1%), Puerto Rican Hispanics (11.3%), and non-Hispanic blacks (8.5%) than among non-Hispanic whites (6.8%) (Table).

Because prevalence estimates for years before 2001 are not comparable to current definitions of asthma prevalence, only a limited number of years are available for trend analysis. The prevalence differences between men and women, adults and children, non-Hispanic whites and non-Hispanic blacks, and poverty levels have not changed since 2001. The multiracial and Puerto Rican race/ethnicity groups are too small to produce reliable single-year estimates for assessing trends.

The results of this analysis are subject to at least four limitations. First, the asthma prevalence estimates in this report rely on self-report and are subject to recall bias. The respondent must correctly recall a physician diagnosis of asthma, which in turn requires that the physician diagnosis was correct and that the diagnosis was conveyed to the person. Because no definitive test exists for asthma, the diagnosis and self-report cannot be validated; however, a 1993 review of asthma questionnaires documented a mean sensitivity of 68% and a mean specificity of 94% when self-reported information on an asthma diagnosis was compared with a clinical diagnosis (1). Second, common to the majority of survey data, results might be biased because of response rates. NHIS is conducted by personal interview and had household response rates between 85% and 87% for the years included in this report. Third, because NHIS includes only the civilian, noninstitutionalized population of the United States, results might not be representative of other populations. Finally, because NHIS is conducted only in English and Spanish, results might not be representative of households whose residents have other primary languages.

The findings of this report indicated that within the U.S. population, current asthma prevalence varied by multiple demographic and economic groups. Asthma was more prevalent among females, children, the poor, the multiracial, and Puerto Rican Hispanics. Findings from this report are comparable to those of previous reports (1,3,4).The exact cause of asthma is unknown, but health management strategies for asthma that take into consideration cultural and population-specific characteristics can reduce the occurrence and severity of asthma exacerbations (8).

Although the reasons for the disparities identified in this report are unclear, observed differences in asthma prevalence among certain demographic and socioeconomic groups (e.g., females, children, non-Hispanic blacks, Puerto Rican Hispanics, and the poor) might be indicators for underlying differences in genetic factors, higher levels of exposure to environmental irritants (e.g., tobacco smoke or air pollutants), and environmental allergens (e.g., house dust mites, cockroach particles, cat and dog dander, and mold). After asthma is diagnosed, heath-care access and actual use of the health- care system, financial resources, and social support are required to manage the disease effectively on a long-term basis (8--10). Research into the role of these factors among disproportionately affected demographic and socioeconomic groups can identify additional asthma control opportunities in these populations. Promoting targeted interventions that take into account cultural differences and population-specific characteristics can improve asthma management and subsequently reduce the asthma burden among disproportionally affected demographic and socioeconomic groups. For children, the use of multitrigger, multicomponent environmental interventions to improve symptom control and reduce missed days of school is recommended (11).

References

1. CDC. National surveillance for asthma---United States, 1980--2004. In: Surveillance Summaries, October 19, 2007. MMWR 2007;56(No. SS-8).
2. National Institutes of Health/National Heart, Lung, and Blood Institute. Expert panel report 3: guidelines for the diagnosis and management of asthma. Bethesda, MD: US Department of Health and Human Services, National Institutes of Health, National Heart, Lung, and Blood Institute, National Asthma Education Program; 2007.
3. Evans R 3rd, Mullally DI, Wilson RW, et al. National trends in the morbidity and mortality of asthma in the US. Prevalence, hospitalization and death from asthma over two decades: 1965--1984. Chest 1987;91(Suppl 6):S65--74.
4. Mannino DM, Homa DM, Akinbami LJ, Moorman JE, Gwynn C, Redd SC. Surveillance for asthma---United States, 1980--1999. MMWR 2002;51(No. SS-1):1--13.
5. Homa DM, Mannino DM, Lara M. Asthma mortality in U.S. Hispanics of Mexican, Puerto Rican, and Cuban heritage, 1990--1995. Am J Respir Crit Care Med 2000;161:504--9.
6. Rose D, Mannino DM, Leaderer BP. Asthma prevalence among US adults, 1998--2000: role of Puerto Rican ethnicity and behavioral and geographic factors. Am J Public Health 2006:96:880--8.
7. CDC. National Health Interview Survey (NHIS), 2007 data release. Hyattsville, MD: US Department of Health and Human Services, CDC, National Center for Health Statistics; 2010. Available at http://www.cdc.gov/NCHS/nhis/nhis_2007_data_release.htm.
8. U.S. Department of Health and Human Services. Healthy people 2010: understanding and improving health. 2nd ed. Washington, DC: U.S. Government Printing Office; 2000. Available at http://www.healthypeople.gov/Document/HTML/Volume2/24Respiratory.htm.
9. Wade S, Weil C, Holden G, et al. Psychosocial characteristics of inner-city children with asthma: a description of the NCICAS psychosocial protocol. National Cooperative Inner-City Asthma Study. Pediatr Pulmonol 1997;24:263--76.
10. Institute of Medicine. Clearing the air: asthma and indoor air exposures. Washington, DC: National Academies Press; 2000.
11. Task Force on Community Prevention Services. Asthma control. The guide to community preventive services. Available at http://www.thecommunityguide.org/asthma/multicomponent.html.

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