Autism is about 10 times as common in the United States today as it was in the 1980s, concludes the largest epidemiological study of the condition yet to be carried out.
The study, conducted in metropolitan Atlanta, Georgia, in 1996 found that 3.4 in every 1000 children aged 3 to 10 years had mild to severe autism, on the basis of a review of their medical records. Surveys before the mid-1980s had found that only 4 to 5 in every 10000 children were affected. The researchers in the Atlanta study, from the federal Centers for Disease Control and Prevention, suggested that some of the increase was the result of widened definitions of the disorder, but the explanation for the rest of the increase was unknown (JAMA 2003;289:49-55).
The definition of autism changed in 1994 to include milder forms of the disorder, such as Asperger's syndrome, in which children lack social skills but are often highly verbal.
Heightened awareness of the disease, and therefore greater propensity to diagnose it, could also have contributed to the increase observed in the Atlanta study. This is “due in large part to efforts of parent and advocacy groups, availability of more medical and educational resources, increased media coverage of affected children and families, and more training and information for physicians, psychologists and other service providers,” the research group said. In 1991, the US Department of Education included autism as a category for special education services, which may also have increased diagnoses.