Arthritis and other rheumatic conditions are among the most prevalent chronic conditions in the United States, affecting an estimated 40 million persons in 1995 and a projected 60 million by 2020 (1). Previous reports have documented marked differences in the prevalence rates of arthritis and related activity limitations by race and ethnicity (1,2), suggesting the relative importance of arthritis might vary among these groups. In addition, race and ethnicity are associated with important differences in health characteristics and must be addressed in efforts to reduce health disparities as specified by the national health objectives for the year 2000 (3). To examine the relative importance of arthritis among these groups, data from the 1989-1991 National Health Interview Survey (NHIS) were used to estimate the prevalence of self-reported arthritis and related activity limitation by race and ethnicity, compare these estimates to those for other chronic conditions, and estimate these prevalences for 2020. Prevalences of Arthritis and Activity Limitation

The NHIS is an annual national probability sample of the civilian, noninstitutionalized population of the United States (4). Estimates of the prevalence of arthritis were based on a one-sixth random sample of 1989-1991 respondents (n=59,289) who answered questions about the presence of any musculoskeletal condition during the preceding 12 months and provided details about these conditions. Each condition was assigned a code from the International Classification of Diseases, Ninth Revision (ICD-9). This analysis used the definition of arthritis, which included arthritis and other rheumatic conditions, developed by the National Arthritis Data Workgroup (1). * Data were weighted to estimate the average annual number of cases and prevalence rates. Because age and sex are strongly associated with arthritis prevalence rates, adjusted rates were estimated using eight age categories (0-24, 25- 34, 35-44, 45-54, 55-64, 65-74, 75-84, and greater than or equal to 85 years) and by sex. Race (white, black, American Indian/Alaskan Native, and Asian/Pacific Islander) and ethnicity (Hispanic, non-Hispanic white, and non-Hispanic black) were determined by the respondent's description of his or her background.

Activity limitation caused by arthritis was estimated by using all respondents in the 1989-1991 NHIS (n=356,592). Respondents were asked if they were unable to perform, or were limited in, their major activity (play or school for children and adolescents; working or keeping house for persons aged 18-69 years; independent living for those aged greater than or equal to 70 years) as a result of health condition(s), and if so, to specify the condition(s) they considered to be responsible for their limitations. Data from those attributing activity limitation to arthritis were weighted to estimate the average annual number of affected persons, prevalence rate, and age- and sex-adjusted rates.

Unadjusted race-specific prevalence rates for arthritis varied from 5.6% (Asians/Pacific Islanders) to 16.0% (whites) (Table_1). Age- and sex-adjusted rates were significantly lower for Asians/Pacific Islanders (7.2% {95% confidence interval (CI)= plus or minus 1.6%}) than for other races (15.2% {95% CI= plus or minus 0.3%} for whites, 15.3% {95% CI= plus or minus 0.8%} for blacks, and 16.5% {95% CI= plus or minus 3.3%} for American Indians/Alaskan Natives). The unadjusted population prevalence rates for activity limitation attributable to arthritis varied from 0.7% (Asians/Pacific Islanders) to 3.0% (blacks and American Indians/Alaskan Natives). Age- and sex-adjusted rates were significantly higher for American Indians/Alaskan Natives (4.2% {95% CI= plus or minus 1.0%}) and blacks (4.0% {95% CI= plus or minus 0.2%}) and significantly lower for Asians/Pacific Islanders (1.1% {95% CI= plus or minus 0.3%}) than for whites (2.7% {95% CI= plus or minus 0.1%}). The proportion of persons with arthritis who had activity limitation attributable to arthritis was lower among whites (17.6%) and Asians/Pacific Islanders (13.0%) than among blacks (24.5%) and American Indians/Alaskan Natives (22.6%).

Unadjusted prevalence rates for arthritis by ethnicity were 6.5% for Hispanics, 12.4% for non-Hispanic blacks, and 16.9% for non-Hispanic whites (Table_1). Age- and sex-adjusted rates were significantly lower for Hispanics (11.2% {95% CI= plus or minus 1.0%}) than for non-Hispanic whites and non-Hispanic blacks (15.5% {95% CI= plus or minus 0.3%} and 15.4% {95% CI= plus or minus 0.8%}, respectively). Unadjusted population prevalence rates for activity limitation were 1.4% for Hispanics and 3.0% for non-Hispanic whites and non-Hispanic blacks. Age- and sex-adjusted rates for activity limitation were similar for Hispanics and non-Hispanic whites (2.7%), and for both groups were significantly lower than for non-Hispanic blacks (3.9% {95% CI= plus or minus 0.2%}). The proportions of persons with arthritis who had activity limitation attributable to arthritis were similar for Hispanics (22.2%) and non-Hispanic blacks (24.3%) and were higher than that for non-Hispanic whites (17.5%). Comparison with Other Chronic Conditions

Average annual prevalence estimates of chronic conditions other than arthritis were based on a one-sixth random sample of NHIS respondents in 1989-1991 who answered questions (on six separate condition lists) regarding the presence of these conditions. Analyses included the 21 most common conditions in the NHIS that were defined as chronic (i.e., a condition lasting greater than 3 months or assumed to be chronic {e.g., diabetes}). These data were weighted to estimate average annual numbers of persons affected. Average annual numbers of persons with activity limitation caused by these chronic conditions were estimated as they were for arthritis.

Arthritis was the most common self-reported chronic condition among whites, the second most common among American Indians/Alaskan Natives and Hispanics, the third most common condition among blacks, and the fourth most common condition among Asians/Pacific Islanders (Table_2). For all groups, arthritis prevalence was higher than self-reported hearing impairment, heart disease, chronic bronchitis, asthma, and diabetes. Among the conditions reported to account for activity limitations, arthritis ranked first among blacks and second among the other groups. Projections for 2020

Arthritis prevalence was projected for 2020 by applying the average annual arthritis prevalence rate for 1989-1991, stratified by age and sex, to the relevant U.S. population projected by the Bureau of the Census (5). Based on these projections, in 2020, self-reported arthritis will affect an estimated 49.7 million whites, 7.0 million blacks, 442,000 American Indians/Alaskan Natives, 1.6 million Asians/Pacific Islanders, and 5.1 million Hispanics. In 2020, activity limitation attributable to arthritis will affect an estimated 9.3 million whites, 1.8 million blacks, 115,000 American Indians/Alaskan Natives, 264,000 Asians/Pacific Islanders, and 1.2 million Hispanics.

Reported by: National Arthritis Data Workgroup. Div of Adult and Community Health, National Center for Chronic Disease Prevention and Health Promotion, CDC.

Editorial Note

Editorial Note: The findings in this report indicate that during 1989-1991, arthritis was the first or among the top four self-reported chronic conditions among all racial/ethnic groups in the United States. As a cause of activity limitation, arthritis ranked either first or second within each group. For these racial groups and for Hispanics, both the large numbers and percentages of persons affected in 1989-1991 probably will increase markedly by 2020, reflecting projected increases in the average age of these populations. Potential explanations for group-specific differences may include variations in cultural thresholds for reporting arthritis (6) and group-specific differences in factors associated with the prevalence of arthritis (e.g., overweight, low socioeconomic status, and occupations involving knee-bending) (7,8). In addition, major histocompatibility genes -- especially molecularly defined alleles -- vary among ethnic groups and are associated with diseases such as rheumatoid arthritis (9).

Although NHIS self-reported data enable more accurate estimates of activity limitation attributable to arthritis than do other sources (e.g., physician-based data) (10), neither the self-reported data nor the assigned ICD-9 codes were validated by a health-care provider. To improve understanding of arthritis and reduce its occurrence and activity limitation attributable to it, public health research and intervention efforts must focus on groups at greatest risk, better define the reasons for these differences among groups, better characterize the epidemiology and natural history of the different types of arthritis, more accurately estimate their economic and societal burden, and evaluate the effectiveness of interventions among these groups. In 1996, six state health departments have initiated use of an optional Behavioral Risk Factor Surveillance System arthritis module to obtain state-level information about arthritis, including data by race and ethnicity. Primary-care providers and state programs can decrease the impact of arthritis among affected groups by 1) promoting primary prevention of arthritis through weight reduction and prevention of sports- or occupational-associated joint injury and 2) encouraging early detection and appropriate education and exercise interventions.

References

1. CDC. Arthritis prevalence and activity limitations -- United States, 1990. MMWR 1994;43:433-8.

2. CDC. Prevalence and impact of arthritis among women -- United States, 1989-1991. MMWR 1995;44:329-34.

3. CDC. Chronic disease in minority populations. Atlanta, Georgia: US Department of Health and Human Services, Public Health Service, CDC, National Center for Chronic Disease Prevention and Health Promotion, 1994:1-1.

4. Massey JT, Moore TF, Parsons VL, Tadros W. Design and estimation for the National Health Interview Survey, 1985-1994. Vital Health Stat {2} 1989;1-5.

5. Day JC. Population projections of the United States, by age, sex, race, and Hispanic origin: 1993-2050. Washington, DC: US Department of Commerce, Bureau of the Census, 1993. (Current population reports; series P25, no. 1104).

6. Berkanovic E, Telesky C. Mexican-American, Black-American, and White-American differences in reporting illnesses, disability, and physician visits for illnesses. Soc Sci Med 1985;20:567-77.

7. Felson DT. Weight and osteoarthritis. J Rheumatol 1995;22(suppl 43):7-9.

8. Leigh JP, Fries JF. Occupation, income, and education as independent covariates of arthritis in four national probability samples. Arthritis Rheum 1991;34:984-95.

9. Schumacher HR Jr, Klippel JG, Koopman WJ. Primer of the rheumatic diseases. 10th ed. Atlanta, Georgia: Arthritis Foundation, 1993:39-40.

10. Edwards S. Evaluation of the National Health Survey diagnostic reporting. Rockville, Maryland: Westat, Inc., December 21, 1992. {Report to NCHS}.

• International Classification of Diseases, Ninth Revision, Clinical Modification, codes 95.6, 95.7, 98.5, 99.3, 136.1, 274, 277.2, 287.0, 344.6, 353.0, 354.0, 355.5, 357.1, 390, 391, 437.4, 443.0, 446, 447.6, 696.0, 710-716, 719.0, 719.2-719.9, 720-721, 725-727, 728.0-728.3, 728.6-728.9, 729.0-729.1, and 729.4.

TABLE 1. Estimated average annual numbers and prevalence rates * of persons with self-reported arthritis + and related
activity limitation in the total population, by race and ethnicity & -- National Health Interview Survey, United States,
1989-1991
========================================================================================================================================================
                                                          Race                                                         Ethnicity
                            --------------------------------------------------------------------   ---------------------------------------------------
                                                                   American           Asian/                              Non-               Non-
                                                                   Indian/           Pacific                           Hispanic           Hispanic
Characteristic                  White              Black        Alaskan Native       Islander         Hispanic           white              black
------------------------------------------------------------------------------------------------------------------------------------------------------
Self-reported arthritis
 No. (thousands)                31,864             3,672               270              401             1,412            30,662             3,533
 Rate (95% CI @)
  Unadjusted                16.0% (+/-0.5%)   12.3% (+/-0.7%)   13.4% (+/-3.5%)   5.6% (+/-1.4%)    6.5% (+/-0.8%)   16.9% (+/-0.4%)   12.4% (+/-0.7%)
  Age- and sex-adjusted     15.2% (+/-0.3%)   15.3% (+/-0.8%)   16.5% (+/-3.3%)   7.2% (+/-1.6%)   11.2% (+/-1.0%)   15.5% (+/-0.3%)   15.4% (+/-0.8%)

Self-reported
 activity limitation
 attributable to arthritis
 No. (thousands)                 5,620               899                61               52               314             5,364              858
 Rate (95% CI)
  Unadjusted                 2.8% (+/-0.1%)    3.0% (+/-0.2%)    3.0% (+/-0.8%)   0.7% (+/-0.2%)    1.4% (+/-0.2%)    3.0% (+/-0.1%)   3.0% (+/-0.2%)
  Age- and sex-adjusted      2.7% (+/-0.1%)    4.0% (+/-0.2%)    4.2% (+/-1.0%)   1.1% (+/-0.3%)    2.7% (+/-0.3%)    2.7% (+/-0.1%)   3.9% (+/-0.2%)

Proportion of persons
 with arthritis who have
 activity limitation
 attributable to arthritis       17.6%             24.5%             22.6%            13.0%             22.2%             17.5%            24.3%
------------------------------------------------------------------------------------------------------------------------------------------------------
* Unadjusted rates are estimated for the 1989-1991 National Health Interview Survey (NHIS) civilian, noninstitutionalized population (CNI),
  using the appropriate weights. Age- and sex-adjusted rates use eight age categories (0-24, 25-34, 35-44, 45-54, 55-64, 65-74, 75-84,
  and >=85 years) to adjust to the 1989-1991 CNI population. To generate national numbers, unadjusted NHIS rates were applied to the
  total population.
+ Arthritis is defined by using the National Arthritis Data Workgroup's definition, which is based on the International Classification of
  Diseases, Ninth Revision, Clinical Modification, codes 95.6, 95.7, 98.5, 99.3, 136.1, 274, 277.2, 287.0, 344.6, 353.0, 354.0, 355.5, 357.1, 390,
  391, 437.4, 443.0, 446, 447.6, 696.0, 710-716, 719.0, 719.2-719.9, 720-721, 725-727, 728.0-728.3, 728.6-728.9, 729.0-729.1, and 729.4.
& Race and ethnicity are self-reported by the respondent.
@ Confidence interval. CIs were calculated using SUDAAN.
========================================================================================================================================================

TABLE 2. Estimated average annual numbers * of persons with self-reported chronic
conditions + and related activity limitations in the civilian, noninstitutionalized
population, by race, ethnicity &, and condition -- National Health Interview Survey,
United States, 1989-1991
====================================================================================================
                                        No.(thousands), by race/ethnicity
                              ------------------------------------------------------
                                                  American
                                                   Indian/       Asian/
                                                   Alaskan      Pacific
Condition                     White      Black     Native       Islander    Hispanic
------------------------------------------------------------------------------------
Top five and selected
 self-reported conditions
 Arthritis @                  31,612     3,678       275          335         1,492
 Chronic sinusitis            28,089     3,745       212          260         1,439
 Deformity or
  orthopedic impairment       24,786     2,556       279          429         1,857
 High blood pressure
  (hypertension)              22,516     4,185       188          338         1,315
 Hearing impairment           19,780     1,486       156          329           979
 Hay fever or allergic
  rhinitis without asthma     19,572     1,823       187          556         1,447
 Heart disease                13,919     1,712        84          154           648
 Chronic bronchitis           10,862     1,093       100          117           731
 Asthma                        9,064     1,578       140          205           926
 Diabetes                      5,163     1,082        91          109           491

Top five and selected
 self-reported conditions
 as a cause of
 activity limitation
 Deformity or orthopedic
  impairment                   6,272       785        96          108           544
 Arthritis                     5,646       908        64           47           327
 Heart disease                 4,107       564        40           39           225
 High blood pressure
  (hypertension)               1,972       797        32           36           205
 Intervertebral disk
  disorders                    1,831       170        20           14           115
 Diabetes                      1,733       497        31           26           216
 Asthma                        1,661       423        23           33           257
 Visual impairment             1,027       151        21           18            87
 Hearing impairment              954        79        11           14            66
 Cerebrovascular disease         841       166         9            6            42
------------------------------------------------------------------------------------
* The average annual number of persons affected in the civilian, noninstitutionalized population
  was estimated by using the appropriate weights in the 1989-1991 National Health Interview
  Survey (NHIS). Data in this table reflect the internal weights of the 1989-1991 NHIS, which are
  based on civilian, noninstitutionalized population estimates that differ slightly from those of
  the 1990 census total population estimates. Using the internal weights of the 1989-1991 NHIS
  allows easier comparison among the different chronic conditions.
+ A condition lasting >3 months or that is assumed to be chronic (e.g., diabetes).
& Race and Hispanic ethnicity are self-reported by the respondent.
@ Arthritis is defined by using the National Arthritis Data Workgroup's definition, which is based
  on the International Classification of Diseases, Ninth Revision, Clinical Modification; other
  chronic conditions are defined by using NHIS chronic condition recode C. Impairments are
  coded according to a special classification system for the NHIS.
====================================================================================================

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