title: Population based study of 12 autoimmune diseases in Sardinia, Italy: prevalence and comorbidity.
abstract: BACKGROUND
  The limited availability of prevalence data based on a representative sample of the general population, and the limited number of diseases considered in studies about co-morbidity are the critical factors in study of autoimmune diseases. This paper describes the prevalence of 12 autoimmune diseases in a representative sample of the general population in the South of Sardinia, Italy, and tests the hypothesis of an overall association among these diseases.
  
  
  METHODS
  Data were obtained from 21 GPs. The sample included 25,885 people. Prevalence data were expressed with 95% Poisson C.I. The hypothesis of an overall association between autoimmune diseases was tested by evaluating the co-occurrence within individuals.
  
  
  RESULTS
  Prevalence per 100,000 are: 552 rheumatoid arthritis, 124 ulcerative colitis, 15 Crohn's disease, 464 type 1 diabetes, 81 systemic lupus erythematosus, 124 celiac disease, 35 myasthenia gravis, 939 psoriasis/psoriatic arthritis, 35 systemic sclerosis, 224 multiple sclerosis, 31 Sjogren's syndrome, and 2,619 autoimmune thyroiditis. An overall association between autoimmune disorders was highlighted.
  
  
  CONCLUSIONS
  The comparisons with prevalence reported in current literature do not show outlier values, except possibly for a few diseases like celiac disease and myasthenia gravis. People already affected by a first autoimmune disease have a higher probability of being affected by a second autoimmune disorder. In the present study, the sample size, together with the low overall prevalence of autoimmune diseases in the population, did not allow us to examine which diseases are most frequently associated with other autoimmune diseases. However, this paper makes available an adequate control population for future clinical studies aimed at exploring the co-morbidity of specific pairs of autoimmune diseases.
authors.affiliation: Dipartimento di Sanità Pubblica, Università di Cagliari, Cagliari, Italy. cla.sardu@tiscali.it
authors.forename: Claudia
authors.initials: C
authors.lastname: Sardu
authors.forename: Eleonora
authors.initials: E
authors.lastname: Cocco
authors.forename: Alessandra
authors.initials: A
authors.lastname: Mereu
authors.forename: Roberta
authors.initials: R
authors.lastname: Massa
authors.forename: Alessandro
authors.initials: A
authors.lastname: Cuccu
authors.forename: Maria Giovanna
authors.initials: MG
authors.lastname: Marrosu
authors.forename: Paolo
authors.initials: P
authors.lastname: Contu
mesh_terms: D015535:Arthritis, Psoriatic / Q000453:epidemiology; D001172:Arthritis, Rheumatoid / Q000453:epidemiology; D001327:Autoimmune Diseases / Q000175:diagnosis / Q000453:epidemiology*; D002446:Celiac Disease / Q000453:epidemiology; D003093:Colitis, Ulcerative / Q000453:epidemiology; D015897:Comorbidity; D003424:Crohn Disease / Q000453:epidemiology; D003922:Diabetes Mellitus, Type 1 / Q000453:epidemiology; D006801:Humans; D007558:Italy; D008180:Lupus Erythematosus, Systemic / Q000453:epidemiology; D015233:Models, Statistical; D009103:Multiple Sclerosis / Q000453:epidemiology; D009157:Myasthenia Gravis / Q000453:epidemiology; D016012:Poisson Distribution; D015995:Prevalence; D011565:Psoriasis / Q000453:epidemiology; D012595:Scleroderma, Systemic / Q000453:epidemiology; D012859:Sjogren's Syndrome / Q000453:epidemiology; D013967:Thyroiditis, Autoimmune / Q000453:epidemiology