THURSDAY, Feb. 8, 2007 (HealthDay News) -- One out of every 150 American eight-year-olds has some form of autism, meaning that 560,000 children in the country have the disorder, the U.S. Centers for Disease Control and Prevention (CDC) said Thursday.
That's a higher prevalence than prior estimates, drawn from a number of countries, that had pegged rates at between 1 in 500 and 1 in 166 children, according to the CDC.
"Autism spectrum disorders (ASD) are a major public health issue," Dr. Marshalyn Yeargin-Allsopp, CDC's chief of the Developmental Disabilities Branch, said during a teleconference about the figures.
The full report is published in the Feb. 9 issue of the agency's journal Morbidity and Mortality Weekly Report.
Overall, some 17 percent of U.S. children have some form of developmental disability, ranging from mild disability, such as speech and language problems, to serious developmental problems, such as intellectual disabilities, cerebral palsy and autism, Yeargin-Allsopp said.
The reasons for the increase in autism spectrum disorders isn't clear, added Catherine Rice, a behavioral scientist at the CDC's National Center on Birth Defects and Developmental Disabilities. "It is difficult to determine exactly what is going on," Rice said during the teleconference. "Is this a change in the way ASDs are identified, or is there an increase for the people at risk for ASDs, such that there is a real increase in the conditions?" she asked.
Rice noted that the definition of these disorders has changed over time. It now includes, in addition to classic autism, Asperger syndrome and other pervasive developmental disorders not otherwise specified.
The CDC data also suggest that there are widespread delays in diagnosing autism spectrum disorders. "The majority of children with an ASD had documented concerns by a parent or a professional before three years of age," Rice noted. "But the median age of earliest ASD diagnosis was approximately four and a half to five and a half years," she said.
To establish the nationwide prevalence of autism spectrum disorders, the CDC looked at school and medical records of children in 2000 and 2002. In 2002, their survey included 10 percent of U.S. eight-year-old children born in 1994 in 14 states, including Alabama, Arizona, Arkansas, Colorado, Georgia, Maryland, Missouri, New Jersey, North Carolina, Pennsylvania, South Carolina, Utah, West Virginia and Wisconsin. The researchers calculated that a total of 2,685 eight-year-olds had autism or a related disorder.
There was a difference in the prevalence of these conditions across states, Rice noted. In 2000, the prevalence of autism spectrum disorders ranged from 4.5 per thousand in West Virginia to 9.9 per thousand in New Jersey, she said.
"Autism prevalence is higher in boys aged eight years than in girls the same age," Rice added. The data indicate that for every girl with an autistic condition, there are three to seven boys with such a disorder, she noted.
In addition, autism spectrum disorders are common among mentally retarded children -- those with an IQ of 70 or less, Rice said. "Between 33 percent and 62 percent of children with an ASD had cognitive impairment," she said.
The CDC is now conducting a study to try to identify the environmental factors that may put children at risk for autism.
One expert believes that earlier diagnosis is essential to help these children.
"This tells us there are an enormous number of children with autism," said Dr. Gary Goldstein, chair of the scientific affairs committee at the advocacy group Autism Speaks, and president and CEO of the Kennedy Krieger Institute in Baltimore, which focuses on pediatric mental health.
Goldstein is particularly concerned that most children with an autism spectrum disorder aren't diagnosed until they start school, despite parents raising concerns years before. "We know that early intervention can be helpful for these children, and it's not going to happen if you're not diagnosed until you are five years old," he said.
These problems can be diagnosed as early as age two, Goldstein said. "It isn't that children begin to show signs of autism at four and five -- all of them who have it at six, had it at two. With proper screening, many more children would be recognized," he said.
In addition, autism and disorders like it are largely genetic conditions, Goldstein said. "If you knew you had it, and you know that your child has a 10 to 15 percent risk of having it, you could use that information," he said.
However, the causes of the various forms of autism aren't known and may be different for each, Goldstein said. "Right now, we have lumped then all in one bucket," he said.
More research is needed to find the causes and treatments for autism, Goldstein said. "By doing the genetic studies and the environmental studies, within a decade, hopefully, we are going to have some real answers," he said. "We don't have prevention, and we don't have treatment right now."
For more information on autism, visit the U.S. National Institute of Mental Health.