title: The incidence of autism in Olmsted County, Minnesota, 1976-1997: results from a population-based study.
abstract: OBJECTIVE
  To determine the incidence of autism among children in Olmsted County, Minnesota.
  
  
  METHODS
  Through the Rochester Epidemiology Project, all inpatient and outpatient diagnoses are indexed for computerized retrieval. This computerized diagnostic index was used to identify children with any developmental disorder. A glossary of symptoms of autism was used to review medical and school records of these children for symptoms consistent with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria for autistic disorder.
  
  
  METHODS
  Olmsted County, Minnesota. Subjects All residents of Olmsted County 21 years or younger between 1976 and 1997. Main Outcome Measure The incidence of research-identified autism based on DSM-IV criteria for autistic disorder.
  
  
  RESULTS
  The age-adjusted incidence of research-identified autism was 5.5 (95% confidence interval, 1.4-9.5) per 100 000 children from 1980 to 1983 and 44.9 (95% confidence interval, 32.9-56.9) from 1995 to 1997 (8.2-fold increase). This increase was confined to children younger than 10 years who were born after 1987.
  
  
  CONCLUSIONS
  The incidence of research-identified autism increased in Olmsted County from 1976 to 1997, with the increase occurring among young children after the introduction of broader, more precise diagnostic criteria, increased availability of services, and increased awareness of autism. Although it is possible that unidentified environmental factors have contributed to an increase in autism, the timing of the increase suggests that it may be due to improved awareness, changes in diagnostic criteria, and availability of services, leading to identification of previously unrecognized young children with autism.
authors.affiliation: Department of Pediatric and Adolescent Medicine, Division of Developmental and Behavioral Pediatrics, Mayo Clinic Dana Child Development and Learning Disorders Program, Mayo Clinic College of Medicine, Rochester, MN 55905, USA. barbaresi.william@mayo.edu
authors.forename: William J
authors.initials: WJ
authors.lastname: Barbaresi
authors.forename: Slavica K
authors.initials: SK
authors.lastname: Katusic
authors.forename: Robert C
authors.initials: RC
authors.lastname: Colligan
authors.forename: Amy L
authors.initials: AL
authors.lastname: Weaver
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Jacobsen
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D001321:Autistic Disorder / Q000175:diagnosis / Q000453:epidemiology*; D002648:Child; D002675:Child, Preschool; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008910:Minnesota / Q000453:epidemiology; D012189:Retrospective Studies