Autism affects about 1 in every 110 American children, a 57 percent increase over the last estimate in 2002, according to a report released yesterday by the U.S. Centers for Disease Control and Prevention.

The disturbing trend reflects greater awareness and diagnosis of "autism spectrum disorders," but may also mean more children are being exposed to the still-mysterious causes, said Catherine Rice, lead author of the CDC report.

"These new numbers are concerning," she said. "We're struggling to find answers. We know complex genetic and environmental factors are involved, and we have much to learn about the causes."

The CDC, Rice said, considers autism "to be a significant public health issue."

Advocacy groups immediately called for more federal funding for research and services.

"We need meaningful action now that acknowledges the scope of the problem and allocates the resources necessary to take the fight against autism to a new level," Bob Wright, cofounder of Autism Speaks, said in a statement.

A Pennsylvania law that went into effect this year calls for parents of autistic children to get up to $36,000 in annual health-insurance benefits.

But many families say the mandate isn't yet working.

Autism includes a range of developmental disorders of varying severity, but the hallmarks are an inability to interact and communicate socially, and compulsive interests and behaviors.

Mental retardation, once thought to be an integral part of autism, was present in only 40 percent of the children identified as autistic in 2006.

It's not clear, Rice said, whether this reflects a diagnostic shift or a change in the autistic population.

Not many decades ago, autism was considered rare.

It has become steadily more common, and in 2002, the CDC estimated the prevalence to be 1 in 150 children.

The latest estimate is based on reviews of records of 8-year-olds in 11 sites across the country - among them, Philadelphia.

In all, 2,757 out of 307,790 children were identified as having some form of autism.

Although the latest autism rates varied geographically, with the lowest in Florida and the highest in Arizona and Missouri, the prevalence increased in all regions, all ethnic and racial groups, and both sexes.

Affected boys continue to outnumber girls by more than 4-1.

In Philadelphia, autism affects 1 in 120 eight-year-olds, up from 1 in 190 in 2002, said Ellen Giarelli, a researcher at the University of Pennsylvania School of Nursing and head of the Pennsylvania autism surveillance program.

She said Philadelphia health professionals have made "great strides" in recognizing autism, and children are now being diagnosed an average of six months earlier than in 2002. Even so, some children are overlooked, which may explain why Philadelphia's rate is slightly lower than the national average, Giarelli said.

Penn and Children's Hospital of Philadelphia are part of a national study, funded by the CDC, that aims to determine the causes of autism, Giarelli said. Through 2011, researchers will be following 2,700 children ages 2 through 5, looking for prenatal, genetic, nutritional and many other possible risk factors.

In addition, Penn's nursing school has begun training a cadre of nurses to recognize autism disorders and help families manage care and therapy.

Experts agree that autistic children usually benefit from early intervention. However, few therapies have been subjected to rigorous studies of effectiveness, and none is considered a gold standard. Behavioral approaches, speech and occupational therapies, medications, special diets, and vitamin injections are available.

Contact staff writer Marie McCullough at 215-854-2720 or mmccullough@phillynews.com.