Autism Increase

http://archpedi.ama-assn.org/cgi/content/short/159/1/37


The Incidence of Autism in Olmsted County, Minnesota, 1976-1997
Results From a Population-Based Study

William J. Barbaresi, MD; Slavica K. Katusic, MD; Robert C. Colligan, PhD;
Amy L. Weaver, MS; Steven J. Jacobsen, MD, PhD


Arch Pediatr Adolesc Med. 2005;159:37-44.

Objective To determine the incidence of autism among children in Olmsted
County, Minnesota.

Design 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.

Setting 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 chidren 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.


Author Affiliations: Department of Pediatric and Adolescent Medicine,
Division of Developmental and Behavioral Pediatrics (Dr Barbaresi),
Department of Health Sciences Research, Division of Epidemiology (Drs
Katusic and Jacobsen) and Division of Biostatistics (Ms Weaver), Department
of Psychiatry and Psychology (Dr Colligan), and Mayo Clinic Dana Child
Development and Learning Disorders Program (Drs Barbaresi and Katusic), Mayo
Clinic College of Medicine, Rochester, Minn.