Increase in autism is due to changes in diagnosis, study claims

BMJ 2004; 328 doi: (Published 12 February 2004) Cite this as: BMJ 2004;328:364
  1. Vittal Katikireddi
  1. BMJ

    The incidence of autism is increasing, but this is due to changes in diagnostic practice, a recent study has found.

    The study, published in December inPharmacotherapy ( 2003;23: 1524-30), set out to identify whether the number of diagnoses of autism had progressively increased over the last decade and, if it had, what environmental exposures were related to the increase.

    “We documented that the number of children [in the United Kingdom] diagnosed with ‘behaviour’ and ‘developmental’ disorders, but not autism, tended to decrease by about 20% per year from 1992 to 2000. By contrast, the diagnosis of autism increased by 20% per year during this time period,” said Hershel Jick, lead author of the study and associate professor of medicine at Boston University School of Medicine.

    “These data point to the conclusion that the increased incidence of diagnosed autism is primarily a reflection of changes in diagnostic practices, such as improved identification, availability of services, and other similar factors,” conclude the authors.

    In the study the authors initially reviewed existing research and found that the incidence of autism had increased.

    “There is convincing evidence that there has been a major increase in the number of children diagnosed as autistic in the United Kingdom, United States, and Denmark,” said Professor Jick.

    The researchers then compared 126 autistic boys with boys who did not have autism and attempted to identify any factors that could be associated with the condition.

    “We found that there was no difference in the frequency of medicines or vaccines, including MMR [the measles, mumps, and rubella vaccine], received by autistic boys compared to normal boys. Similarly, there was no difference in the medicines or illnesses present in the mothers of autistic boys during pregnancy compared to mothers of normal boys. We conclude that neither medicines nor medical illness were responsible for the increase in autistic children over time,” Professor Jick said.

    “The study also provides compelling evidence that vaccines, including MMR, are not the cause of the rise,” he added.

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