EPIDEMIOLOGY AND ESTIMATED POPULATION BURDEN OF SELECTED AUTOIMMUNE-DISEASES IN THE UNITED-STATES

Autoimmune diseases cause significant and chronic morbidity and disabi lity. The actual number of persons in the United States that are affec ted by autoimmune diseases and the resultant magnitude of their impact on the public's health are limited to a few specific diseases. In ord er to understand the clinical, public health and economic importance o f these diseases it is necessary to have estimates of incidence and pr evalence rates in the population. In this analysis, we estimate the nu mber of persons affected by 24 autoimmune diseases in the United State s by applying mean weighted prevalence and incidence rates obtained fr om published articles to U.S. Census data. The study was restricted to 24 autoimmune predefined diseases for which there was direct or indir ect evidence for autoimmune pathogenesis. Subsequently, we used comput erized search software and ancestry searching (bibliographies) to cond uct a comprehensive search of articles published from 1965 to the pres ent. Eligible studies included those which adhered to standard disease definitions and which included population-based estimates of incidenc e or prevalence rates. Mean weighted incidence and prevalence rates we re calculated from eligible published studies with greater weight prop ortionately given to larger studies. The mean rates were then applied to the U.S. Census population figures to estimate the number of person s currently afflicted with each disease and the number of new cases oc curring 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, regardle ss of country of origin. The number of eligible incidence and prevalen ce studies found in the literature varied considerably between the 24 autoimmune diseases selected. The largest number of eligible prevalenc e studies were conducted on multiple sclerosis (MS), rheumatoid arthri tis, and systemic lupus erythematosus (SLE) (greater than or equal to 23), followed by insulin-dependent diabetes (IDDM), myasthenia gravis, primary biliary cirrhosis, and scleroderma (greater than or equal to 7). There were only one to four eligible studies done on 11 other dise ases, 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! hyperthyroidis m, glomerulonephritis, primary biliary cirrhosis, rheumatic fever, rhe umatoid arthritis, scleroderma, and SLE (greater than or equal to 9). On the other II diseases, there were one to six eligible studies, and no studies on 5 diseases. There were no eligible incidence or prevalen ce studies on Goodpasture's syndrome, idiopathic thrombocytopenia purp ura, or relapsing polychondritis. Overall we estimate that 8,511,845 p ersons in the United States or approximately 1 in 31 Americans are cur rently afflicted with one of these autoimmune diseases. The diseases w ith the highest prevalence rates were Graves'/hyperthyroidism, IDDM, p ernicious anemia, rheumatoid arthritis, thyroiditis, and vitiligo, com prising an estimated 7,939,280 people or 93% of the total number estim ated. Glomerulonephritis, MS, and SLE added an estimated 323,232 peopl e. The prevalence of the other diseases reviewed were rare, less than 5.14/100,000. Most diseases were more common in women. From the incide nce data we estimate that 237,203 Americans will develop an autoimmune disease in 1996 and that approximately 1,186,015 new cases of these a utoimmune diseases occur in the United States every 5 years. Women wer e 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 dise ases are infrequently studied by epidemiologists. As a result the tota l burden of disease may be an underestimate. The number of studies per formed on a disease has not necessarily been related to the public hea lth burden of the conditions reviewed. Individual autoimmune diseases have often been studied as separate entities; however, many share comm on mechanisms of induction and pathogenesis. Thus, considered as a gro up of disorders autoimmune diseases are an important cause of morbidit y and affect a large number of Americans. Further epidemiologic resear ch is urgently needed to improve our understanding of the prevalence a nd incidence of autoimmune disorders, their medical and public health impact, and the cost to the U.S. health system, especially in terms of health service delivery and diagnosis. (C) 1997 Academic Press.