New York Times
1 January 2003

Prevalence of Autism Growing, Study Finds
By Sandra Blakeslee

Autism is about 10 times more prevalent today than it was in the 1980's, according to the largest United States study ever on the problem. Some of the increase can be explained by widened definitions of the disorder, the researchers said, but the explanation for the rest of the increase is unknown.

The study, conducted in metropolitan Atlanta in 1996, found that 3.4 in every 1,000 children between the ages of 3 and 10 had diagnoses of mild to severe autism during that year. In the late 1980's, 4 to 5 out of every 10,000 children were thought to be afflicted.

The higher prevalence rate, described in today's issue of the Journal of the American Medical Association, is in line with rates found in recent but smaller studies here and abroad in which the prevalence rate of autism is 4 to 6 out of every 1,000 children.

The researchers, from the federal Centers for Disease Control and Prevention, said the prevalence rates they found would mean that at least 425,000 American children under age 18 have some form of autism, including 114,000 children under age 5.

Dr. Marshalyn Yeargin-Allsop, an epidemiologist at the National Center on Birth Defects and Developmental Disabilities, led the new study which was carried out in the federal agency's backyard of metropolitan Atlanta.

Some of the increased prevalence can be explained by changes in the definition of autism, a brain disorder in which normal social interaction is difficult or impossible. In recent years, the definition has been widened to include milder forms of the disorder.

Most experts believe autism results from an interplay of genes and unknown environmental factors. "No strong candidate environmental exposures have been identified," said Dr. Eric Fombonne, an autism expert at McGill University and the Montreal Children's Hospital in Quebec. "Claims of an association with measles-mumps-rubella immunization have not been borne out by recent studies, and evidence for causal association with other exposures, such as mercury containing vaccines, is weak."

Portia Iversen, the mother of an autistic child and the co-founder of Cure Autism Now, an advocacy group in Los Angeles, said the findings reported today were not surprising. "We are in the midst of an autism epidemic in this country," she said. We need the government to step in and take emergency action."

Dr. Yeargin-Allsop said the researchers canvassed schools, clinics, physicians, non-profit programs and other places autistic children might go for services in 1996. Studies that look at autistic children in just one setting, such as special clinics, tend to find lower prevalence rates, she said.

Experts reviewed the medical records of each child and determined if autism was diagnosed accurately. They did not examine the children in person. Out of the 289,456 children between the ages of 3 and 10 years living in the five counties of metropolitan Atlanta in 1996, 987 had mild to severe autism, giving a prevalence rate of 3.4 per thousand.

Dr. Yeargin-Allsop said 18 percent of the children found to have autism in 1996 had never been diagnosed accurately. Many were classified as having general developmental difficulties whereas higher functioning children were missed entirely.

The Atlanta study found that prevalence rates were the same for black and white children, but confirmed earlier studies that autism is four times more common in boys than in girls.

Dr. Yeargin-Allsop said the federal agency is conducting similar surveillance studies across several states to provide a more complete picture of autism.