The first national survey of autism incidence confirms the widely held belief that the debilitating disorder has become widespread, afflicting an estimated 300,000 U.S. schoolchildren – about one in every 175.

The new estimates contrast sharply with estimates of one in every 2,000 children that were commonly used only two decades ago, and there has been great controversy about whether the higher prevalence reflects a sharply increased rate of the disorder, better detection or even overdiagnosis by doctors.

Autism and its related developmental disorders “are an urgent public health issue that affect the lives of many, many families,” Dr. Jose Cordero of the Centers for Disease Control and Prevention said Thursday in releasing the new figures. “The cost is in the billions of dollars.”

The new results are not surprising, said Dr. Melissa Nishawala, an autism specialist at the New York University School of Medicine.

“These numbers are not so different from the one in 166 that has been in use for a long time,” she said.

The new study, reported Thursday in the CDC’s Morbidity and Mortality Weekly Report, does not address the causes of autism or trends in incidence.

Autism is a severe developmental disorder in which children seem isolated from the world around them. There is a broad spectrum of symptoms, marked by poor language skills and an inability to handle social relations. No cure exists, but many problems can be alleviated with behavioral therapy.

Some autism advocacy groups have argued that the measles-mumps-rubella vaccine and the use of mercury as a preservative in a variety of childhood vaccines are responsible for the growing number of cases. But most studies have failed to confirm such a link and the cause of the increase remains a mystery.