Rate of Autism May Be Increasing

Laurie Barclay, MD

December 31, 2002

Dec. 31, 2002 — The rate of autism in the Atlanta area in 1996 was higher than U.S. rates during the 1980s and early 1990s, according to results of a study published in the Jan. 1 issue of The Journal of the American Medical Association. However, the rate is consistent with that reported in more recent studies.

"Debate continues about whether the overall prevalence of autism has increased or whether past rates underestimated true prevalence," write Marshalyn Yeargin-Allsopp, MD, from the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, and colleagues.

Studies published before 1985 showed prevalence rates of 4 to 5 per 10,000 children for the autism spectrum overall and approximately 2 per 10,000 for classic autism. Subsequent non-U.S. studies have reported rates of 7 to 10 per 10,000 children for classic autism and 1.5 to 2.5 times those rates for autism spectrum disorders, such as a recent U.K. study which showed a prevalence of 16.8 per 10,000 children for classic autism and 62.6 per 10,000 for the autism spectrum.

Using records from medical centers and schools, the CDC investigators determined the prevalence of autism in children aged 3 to 10 years in metropolitan Atlanta in 1996. Diagnoses in the 987 children identified with autism included autistic disorder, pervasive developmental disorder not otherwise specified, or Asperger syndrome. Schools were the only institution identifying 40% of children with autism, and schools were the most important source of information on black children, children of younger mothers, and children of mothers with less than 12 years of education.

The prevalence of autism was 3.4 per 1,000, with a male-to-female ratio of 4:1, and comparable rates were seen in black and white children. "This overall rate is 10 times higher than rates from three other U.S. studies that used similar, specific criteria to identify children with autism and pervasive developmental disorders in the 1980s and early 1990s," the authors write.

Several factors that could contribute to the increased rate of recognized autism may include changes in diagnostic criteria to cover a wider spectrum of autistic disorders, heightened public awareness and media coverage, and addition of autism as a category meriting special education services by the U.S. Department of Education in 1991.

In an accompanying editorial, Eric Fombonne, MD, from McGill University in Montreal, Quebec, notes that this is the first study to demonstrate a population-based estimate for the rate of autism spectrum disorder in black children, which is comparable to that of other racial groups. However, other findings were similar to those of other earlier studies, including strong male predominance, cognitive impairment in more than two-thirds of cases, and a relatively high rate (8%) of epilepsy.

Because about 18% of cases were not suspected of having autism, and because schools were often the only source of case finding, he writes that "these findings highlight the need to rely on multiple ascertainment sources in epidemiological studies of autistic spectrum disorder and caution against findings that are based on single service provider databases."

JAMA. 2003;289:49-55, 87-89

Reviewed by Michael W. Smith, MD

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