Epidemiology and estimated population burden of selected autoimmune diseases in the United States

Abstract

Autoimmune diseases cause significant and chronic morbidity and disability. The actual number of persons in the United States that are affected by autoimmune diseases and the resultant magnitude of their impact on the public's health are limited to a few specific diseases. In order to understand the clinical, public health and economic importance of these diseases it is necessary to have estimates of incidence and prevalence rates in the population. In this analysis, we estimate the number of persons affected by 24 autoimmune diseases in the United States by applying mean weighted prevalence and incidence rates obtained from published articles to U. S. Census data. The study was restricted to 24 autoimmune predefined diseases for which there was direct or indirect evidence for autoimmune pathogenesis. Subsequently, we used computerized search software and ancestry searching (bibliographies) to conduct a comprehensive search of articles published from 1965 to the present. Eligible studies included those which adhered to standard disease definitions and which included population-based estimates of incidence or prevalence rates. Mean weighted incidence and prevalence rates were calculated from eligible published studies with greater weight proportionately given to larger studies. The mean rates were then applied to the U.S. Census population figures to estimate the number of persons currently afflicted with each disease and the number of new cases occurring each year in the United States. Only U.S. and European studies were used to estimate prevalence and incidence rates when there were at least six eligible studies available for a disease. When there were fewer than six studies, all available studies were included, regardless of country of origin. The number of eligible incidence and prevalence studies found in the literature varied considerably between the 24 autoimmune diseases selected. The largest number of eligible prevalence studies were conducted on multiple sclerosis (MS), rheumatoid arthritis, and systemic lupus erythematosus (SLE) (>/=23), followed by insulin-dependent diabetes (IDDM), myasthenia gravis, primary biliary cirrhosis, and scleroderma (>/=7). There were only one to four eligible studies done on 11 other diseases, and no prevalence studies on 6 diseases. Incidence studies were less frequent but the largest number of studies were conducted on IDDM (n = 37) and MS (n = 28), followed by Graves' disease/hyperthyroidism, glomerulonephritis, primary biliary cirrhosis, rheumatic fever, rheumatoid arthritis, scleroderma, and SLE (>/=9). On the other 11 diseases, there were one to six eligible studies, and no studies on 5 diseases. There were no eligible incidence or prevalence studies on Goodpasture's syndrome, idiopathic thrombocytopenia purpura, or relapsing polychondritis. Overall we estimate that 8,511,845 persons in the United States or approximately 1 in 31 Americans are currently afflicted with one of these autoimmune diseases. The diseases with the highest prevalence rates were Graves'/hyperthyroidism, IDDM, pernicious anemia, rheumatoid arthritis, thyroiditis, and vitiligo, comprising an estimated 7,939, 280 people or 93% of the total number estimated. Glomerulonephritis, MS, and SLE added an estimated 323,232 people. The prevalence of the other diseases reviewed were rare, less than 5.14/100,000. Most diseases were more common in women. From the incidence data we estimate that 237,203 Americans will develop an autoimmune disease in 1996 and that approximately 1,186,015 new cases of these autoimmune diseases occur in the United States every 5 years. Women were at 2.7 times greater risk than men to acquire an autoimmune disease. After reviewing the medical literature for incidence and prevalence rates of 24 autoimmune diseases, we conclude that many autoimmune diseases are infrequently studied by epidemiologists. As a result the total burden of disease may be an underestimate. (ABSTRACT TRUNCATED)