The rates, based on 2010 data, were up 30 percent from two years earlier. They have more than doubled both nationwide and in New Jersey since the first report was done in 2000. The CDC estimates that 1.2 million people under the age of 21 are on the autism spectrum.
Walter Zahorodny, an epidemiologist and psychologist at Rutgers New Jersey Medical School who directed data collection in New Jersey, said the new report should put to rest the argument over whether the increase in autism diagnoses stems from growing awareness or reflects growing numbers of children with the disabling condition.
"It's a true increase," he said. "It's a change of great magnitude. It's silly to go on debating that." He expects the numbers to climb higher before they plateau.
Jennifer Pinto-Martin, an epidemiologist in the University of Pennsylvania School of Nursing who worked on previous versions of the report, is not so sure. While the CDC has been using the same definition for many years, she said, changing attitudes have made it easier to get the diagnosis.
Both agreed that one reason New Jersey's numbers are high is that the state has particularly good record-keeping and services.
At a CDC briefing for reporters on Thursday, Coleen Boyle, director of the National Center on Birth Defects and Developmental Disabilities, sidestepped the "why" question by saying there is evidence that some of the increase is due to changes in diagnosis without elaborating on what is responsible for the rest of it.
The report, which is based on 2010 data, looked at the prevalence of autism among 8-year-olds in parts of 11 states. Overall, 14.7 out of every 1,000 children had an autism spectrum disorder. The part of New Jersey studied - Essex, Union, Hudson and Ocean counties - had 21.9. A similar report based on 2000 and 2002 data put the New Jersey rate at almost half that: 10.6 per 1,000.
Pennsylvania was not included in the most recent report. Pinto-Martin said it dropped out because researchers were unable to get education data, which is used to augment information from health-care providers. The four states included in Thursday's report that did not have school data all had lower autism rates than states that gave the CDC access to more information.
Nationally, the rate per 1,000 was 6.7 in 2000, 8.0 in 2004, 9 in 2006 and 11.3 in 2008.
Symptoms for people who are on the autism spectrum can range from mild to severe. The disorder is characterized by communication problems, obsessional interests and repetitive movements. Diagnosis is based on symptoms, not a medical test. The median age of diagnosis is about 4-1/2 years.
In successive reports over time, a growing proportion of children characterized as autistic have been of normal intelligence. Thirty-two percent were average or above in 2002, compared to 46 percent in 2010, the new report said.
The official description of autism changed last year when a new verson of the Diagnostic and Statistical Manual of Mental Disorders, the DSM-5, was published. The new CDC report used the old definition. Some autism advocates are concerned that the new definition will reduce the number of children with the diagnosis, leaving fewer kids eligible for special services.