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About 300,000 school-age children in the United States have been diagnosed with autism, according to two comprehensive federal surveys of parents.

The surveys, conducted by the U.S. Centers for Disease Control and Prevention, are described as their first national estimates of the prevalence of autism, a neurological disorder characterized by social impairments and repetitive behaviors.

One survey was conducted by phone polling and the other by door-to-door visits, but their results were similar to each other鈥檚 and to more localized autism-prevalence studies conducted earlier.

The National Health Interview Survey, conducted by the Atlanta-based CDC during home visits in 2003 and 2004, yielded an estimate of 5.7 children diagnosed with autism per 1,000 school-age children. The National Survey of Children鈥檚 Health, also conducted by the CDC over the phone, gave an estimated prevalence of 5.5 per 1,000 school-age children.

In both surveys, parents were asked whether a health-care provider had ever told them that their child had autism. Both surveys indicated that boys are nearly four times more likely than girls to be diagnosed with autism.

The surveys did not address, however, whether autism cases are on the rise.

鈥淭he surveys can鈥檛 tell us much about autism trends. These surveys are designed to provide us a snapshot, a picture of the world at a given point in time,鈥� Dr. Jose Cordero, the director of the CDC鈥檚 National Center on Birth Defects and Developmental Disabilities, said in a transcript of a press conference held on May 4, the day the survey results were released.

鈥淭aken together, these studies confirm that autism is a condition of major public-health concern that affects many families,鈥� he said.

Growth Factor

The causes of autism, and whether autism cases are growing in frequency, have been the topic of fierce debate. Using data gathered by the U.S. Department of 91制片厂视频, some advocates argue that the number of autism cases is growing rapidly. They also say there鈥檚 a link between the neurological disorder and environmental factors such as exposure to mercury used as a preservative in vaccines.

But a study published in the April issue of the journal Pediatrics concludes that the 91制片厂视频 Department data are too unreliable for statisticians to use. That study suggests that the cases of reported autism may be increasing because more health-care workers are aware of the disorder, and are diagnosing children as having autism rather than other disabilities, such as mental retardation.

The CDC plans to continue its research so that it can more accurately report any trends, said Dr. Cordero. However, even as a snapshot of autism cases in 2003 and 2004, when the surveys were conducted, the research yielded interesting data, he said.

is available from the U.S. Centers for Disease Control and Prevention鈥檚 .

In addition to the likelihood that boys would be diagnosed with autism more often than girls, the prevalence of autism was higher among children ages 6 to 11, among non-Hispanic whites, in households where at least one member had education that went beyond high school, and in families whose income was more than twice the federal poverty level. The different prevalence rates suggest that, even though autism can be diagnosed for children as young as 18 months, most children are diagnosed with autism when they enter school, CDC officials said.

Dr. Gary W. Goldstein, the president and chief executive officer of the Kennedy Krieger Institute in Baltimore, which focuses on treatment, research, and education for children with developmental disabilities, said the results suggest that surveying parents can yield results similar to those of more intensive, time-consuming studies. That knowledge about methodology may make it easier to map autism trends, he said.

鈥淭he advantage is that this is repeatable, so you can be doing this over and over,鈥� said Dr. Goldstein, who is also a board member of Autism Speaks, a research- and funding-advocacy group based in New York City.

Focus on Intervention

The disparity in diagnosis prevalence among racial minorities and the poor, compared with children from white and more affluent families, suggests that doctors should take an active role in assessing children, even if parents aren鈥檛 pushing for a diagnosis, he said.

The results of the surveys 鈥渋mply to me that this is a diagnosis that families have to have the energy to pursue. Families have to be their own advocates in this,鈥� Dr. Goldstein said, especially because early intervention has been shown to be important for children with autism.

Lee Grossman, the president and chief executive officer of the Autism Society of America, located in Bethesda, Md., said that it is important to analyze the numbers and search for causes of the disorder. But that search should not obscure the need to get more help to families struggling with autism now.

鈥淲e need to change the debate,鈥� Mr. Grossman said. 鈥淲e need to look at the numbers, but let鈥檚 move into providing interventions and other services. This is an issue that is currently a national health priority, and resources need to be put forward to address it.鈥�