Asthma Hospitalizations and Readmissions Among Children and Young Adults -- Wisconsin, 1991-1995

Asthma is the most frequent reason for preventable hospital admissions among children (1,2). During 1980-1993, national asthma surveillance demonstrated increasing rates of hospital admission for persons aged less than 25 years (3). These increasing rates could be attributed to an increase in either the number of persons admitted, readmitted, or both (4). To determine the number of persons with asthma sufficiently severe to require hospitalization and to characterize admission/readmission patterns for persons with asthma, the Wisconsin Department of Health and Family Services (WDHFS) analyzed data from the Wisconsin Asthma Surveillance System (WASS). This report summarizes the findings from WASS, which indicate that, during 1991-1995, an annual average of 18% of all asthma admissions among Wisconsin residents aged less than 25 years were readmissions.

WDHFS analyzed hospital discharge data from WASS to identify all hospital admissions for asthma during 1991-1995 among Wisconsin residents aged less than 25 years. In Wisconsin, all hospitals are required to report discharge data to the state health department. Admissions were considered asthma related if the primary diagnosis was asthma (International Classification of Diseases, Ninth Revision, Clinical Modification {ICD-9-CM}, code 493) or if the primary diagnosis was respiratory illness (ICD-9-CM codes 460-496) with a second or third diagnosis of asthma. In this analysis, the number of asthma-related admissions does not equal the number of persons admitted to a hospital for asthma because some persons were readmitted for asthma during the specified time periods. An admission was classified as a readmission if two or more database entries matched on 1) hospital and medical record number or 2) encrypted patient identifier, date of birth, sex, and zip code. Transfer admissions were excluded from analysis. Race-specific analyses were restricted to blacks and whites because numbers for other racial groups were too small to calculate stable estimates. Rates were age adjusted to the 1990 Wisconsin census. Denominators for all rates were U.S. Bureau of the Census intercensal estimates for Wisconsin.

During 1991-1995, a total of 11,804 Wisconsin residents aged less than 25 years accounted for 17,678 hospital admissions for asthma. Of these admissions, 82% had a primary discharge diagnosis of asthma, 15% had a primary diagnosis of respiratory illness and a second diagnosis of asthma, and 3% had a primary diagnosis of respiratory illness and a third diagnosis of asthma. During this 5-year period, 33% of all asthma-related admissions were readmissions, and 26% of the persons admitted for asthma accounted for 51% of all asthma-related admissions.

During 1991-1995, the average annual number of asthma-related admissions among persons aged less than 25 years was 3535; of these, 616 (18%) were readmissions (Table_1). On average, blacks were five times more likely than whites to be admitted to a hospital for asthma (64 versus 13 per 10,000 persons aged less than 25 years, pless than 0.001). For blacks and whites, readmissions accounted for 23% and 15%, respectively, of all asthma-related admissions. In addition, blacks were approximately 50% more likely than whites to be readmitted to a hospital for asthma (19% versus 12%, pless than 0.001).

Based on age-specific data, the average annual number of asthma-related admissions was highest for persons aged 0-4 years (1661); of these, 384 (23%) were readmissions. In contrast, among persons aged 5-14 years and 15-24 years, 13% and 12% of all asthma-related admissions, respectively, were readmissions.

During 1991-1995, the annual asthma admission rate remained relatively unchanged (Table_2). For each year of this period, 17%-18% of all asthma-related admissions were readmissions.

Reported by: J Goldring, PhD, L Hanrahan, PhD, HA Anderson, MD, Environmental/Occupational Epidemiologist, PL Remington, MD, Chronic Disease Epidemiologist, Div of Health, Wisconsin Dept of Health and Family Svcs. Div of Applied Public Health Training (proposed), Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: One national health objective for the year 2000 is to reduce asthma admissions to less than 19 per 10,000 persons (objective 11.1) (5). The data from WASS in this report indicate that Wisconsin's asthma admission rate during 1991-1995 was 20 admissions per 10,000 persons aged less than 25 years. However, using the number of persons admitted at least once for asthma in the numerator rather than the number of admissions, the average annual asthma admission rate during this period was 17 persons per 10,000. The percentage difference in these two rates (18%) resulted from readmission of persons previously admitted for asthma during the year.

Characterization of risk factors for asthma-related readmission can enable development of interventions to prevent readmissions. The high frequency of asthma-related admissions and the disporportionate number of readmissions among blacks suggest that efforts to reduce asthma-related admissions should target persons who have been hospitalized for asthma. Previous studies indicate that the race-specific differences in asthma admission rates are associated with socioeconomic status (6,7).

The findings in this report are subject to at least two limitations. First, erroneous data entry of any of the six variables used to identify persons admitted to a hospital for asthma could result in misclassification of an event as an incident admission instead of a readmission. Similarly, patients who move within the state may not be correctly identified as prevalent cases.

The findings from WASS highlight the importance of analyzing longitudinal, patient-specific data about asthma. Although most states collect hospital discharge data that can be used for asthma surveillance, few states have asthma surveillance programs (8).

Ongoing surveillance is necessary to assess the impact of practice guidelines and interventions (9) to prevent asthma hospitalizations. WASS can monitor the impact of intervention efforts on asthma admission and readmission rates and the number of persons requiring hospitalization for asthma. Patient-specific data provide more detailed information about the burden of asthma than admission data alone and can augment admission rates as a benchmark in assessing progress toward improved management of asthma.

References

1. Billings J, Zeitel L, Lukomnik J, Carey TS, Blank AE, Newman L. Impact of socioeconomic status on hospital use in New York City. Health Aff 1993;12:162-73.

2. Weissman JS, Gatsonis C, Epstein AM. Rates of avoidable hospitalization by insurance status in Massachusetts and Maryland. JAMA 1992;268:2388-94.

3. CDC. Asthma mortality and hospitalization among children and young adults -- United States, 1980-1993. MMWR 1996;45:350-3.

4. To T, Dick P, Feldman W, Hernandez R. A cohort study on childhood asthma admissions and readmissions. Pediatrics 1996;98:191-5.

5. Public Health Service. Healthy people 2000: national health promotion and disease prevention objectives -- full report, with commentary. Washington, DC: US Department of Health and Human Services, Public Health Service, 1991; DHHS publication no. (PHS)91-50212.

6. Wissow LS, Gittelsohn AM, Szklo M, et al. Poverty, race, and hospitalization for childhood asthma. Am J Public Health 1988;78:777-82.

7. Halfon N, Newacheck PW. Childhood asthma and poverty: differential impacts and utilization of health services. Pediatrics 1993;91:56-61.

8. National Heart, Lung, and Blood Institute. National Asthma Education and Prevention Program Task Force on the Cost Effectiveness, Quality of Care, and Financing of Asthma Care. Bethesda, Maryland: US Department of Health and Human Services, Public Health Service, National Institutes of Health, 1996; DHHS publication no. (NIH)55-807.

9. CDC. Asthma surveillance programs in public health departments -- United States. MMWR 1996;45:802-4.

TABLE 1. Average annual number and rate * of asthma-related admissions and percentage of readmissions for persons aged <25 years, by race +
and age group -- Wisconsin, 1991-1995
==============================================================================================================================================
                                                                                     Admission rate   % Readmissions &    % Readmissions @
Characteristic    No. admissions   No. persons admitted    Admission rate (events)     (persons)      (hospitalizations)      (persons)
----------------------------------------------------------------------------------------------------------------------------------------------
Race **
  Black                1118                 864                     82.4                  63.7             22.8%                18.6%
  White                2417                2055                     14.8                  12.6             14.9%                11.7%
Age group (yrs)
   0- 4                1661                1277                     48.8                  37.5             23.1%                15.5%
   5-14                1209                1058                     16.3                  14.3             12.5%                13.2%
  15-24                 665                 584                      9.7                   8.5             12.2%                13.5%

Total **               3535                2919                     20.0                  16.5             17.5%                13.8%
----------------------------------------------------------------------------------------------------------------------------------------------
*  Per 10,000 persons aged <25 years per year.
+  Numbers for racial groups other than black and white were too small to calculate stable estimates.
&  Percentage of total. Admissions minus persons admitted divided by admissions.
@  Percentage of total during the year.
** Age-adjusted to the 1990 Wisconsin census.
==============================================================================================================================================

TABLE 2. Number and rate * of asthma-related admissions and percentage of readmissions for persons aged <25 years, by year -- Wisconsin,
1991-1995
=========================================================================================================================================
                                                                           Admission rate     % Readmissions +     % Readmissions &
Year   No. admissions   No. persons admitted    Admission rate (events)      (persons)        (hospitalizations)       (persons)
-----------------------------------------------------------------------------------------------------------------------------------------
1991        3583                2941                     20.4                   16.7               17.9%                  15.3%
1992        3712                3050                     21.1                   17.3               17.8%                  14.8%
1993        3848                3175                     21.7                   17.9               17.5%                  14.4%
1994        3127                2603                     17.7                   14.7               16.8%                  10.5%
1995        3408                2825                     19.3                   16.0               17.1%                  13.9%
-----------------------------------------------------------------------------------------------------------------------------------------
* Per 10,000 persons aged <25 years. Age-adjusted to the 1990 Wisconsin census.
+ Percentage of total. Admissions minus persons admitted divided by admissions.
& Percentage of total during the year.
=========================================================================================================================================

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