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US study shows 10-fold increase in autism over the past 20 years

BMJ 2003; 326 doi: (Published 11 January 2003) Cite this as: BMJ 2003;326:71
  1. Scott Gottlieb
  1. New York

    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 in the before the mid-1980s had found that only 4 to 5 in every 10 000 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.

    In the latest study, researchers reviewed the medical records of each child and determined whether autism had been diagnosed accurately. They did not examine the children. Of the 289 456 children aged 3 to 10 living in the metropolitan area of Atlanta in 1996, 987 had mild to severe autism. Dr Marshalyn Yeargin-Allsop, an epidemiologist at the National Center on Birth Defects and Developmental Disabilities, who led the study, said that 18% of the children found to have autism in 1996 had never had an accurate diagnosis. Many had been classified as having general developmental difficulties; the higher functioning children had been missed entirely. The prevalence of autism found in the study would mean that at least 425 000 Americans aged under 18 years have some form of autism.

    The increased prevalence of autism in the Atlanta study mirrors increases reported elsewhere. Many teachers, paediatricians, and social workers across the United States have reported soaring numbers of cases of autism in the 1990s. The US Education Department reported a 544% increase in autistic students from 1992 to 2000. In California, the number of autistic children in social services records nearly quadrupled between 1987 and 1998. However, officials from the Centers for Disease Control and Prevention warned that these figures might be misleading because they measure the number of children enrolling in services and not the occurrence of autism.