One in 88 American children has an autism spectrum disorder, according to a new estimate from the U.S. Centers for Disease Control and Prevention.

The rate is 23 percent higher than one the agency released three years ago. Federal officials said some of the increase is attributable to better diagnoses, though it's not clear how much.

"We don't know what causes autism, but a lot of children have autism," said Li-Ching Lee, a psychiatric epidemiologist at the Johns Hopkins University's Bloomberg School of Public Health and the principal investigator for the CDC's Maryland data.

Maryland is among 14 states researchers sampled for the study, and the state's incidence of autism is even higher than the national rate. One in 80 of the state's children is estimated to have the disorder, based on a survey of 8-year-olds in 2008.

That's up 35 percent from 1 in 109 such children two years earlier.

"One thing the data tells us with certainty: There are many children and families who need help," said Dr. Thomas Frieden, CDC director, during a news conference Thursday. "We must continue to track autism spectrum disorders because this is the information communities need to guide improvements in services to help children."

The CDC revises its estimate every few years, and the rate has been steadily increasing. Since 2002, the number of children with autism diagnoses has increased 78 percent.

"Autism is officially becoming an epidemic," said Mark Roithmayr, president of the advocacy group Autism Speaks, during the news conference. "The United States is dealing with a national emergency that is in need of a national plan."

This rise comes with enormous costs, Roithmayr said. His group estimates that $137 billion a year is now spent on the disorder.

He called for more screening and treatment dollars, as well as more workforce training to deal with children and adults with the disorder.

In releasing the data, local and federal officials agreed that more needs to be done to ensure all children are screened and provided treatment.

Nationally and in Maryland, autism is diagnosed five times more often in boys. The new CDC data show 1 in 54 boys with the disorder. In Maryland, it was 1 in 49 boys.

The largest increases nationwide were among Hispanic and black children, though in Maryland there was no such disparity.

The data varied greatly from state to state. In Alabama, 1 in 210 children was diagnosed with autism, while the figure was 1 in 47 children in Utah. This might reflect the sample size and the types of data assessed, Lee said.

Researchers in Maryland reviewed school and health insurance records, focusing on more than 27,000 children who were age 8 in 2008 and lived in Anne Arundel, Baltimore, Carroll, Cecil, Harford and Howard counties. All had some indication of a developmental or behavior disorder, including almost three quarters of the children who already had an autism diagnosis.

There is no medical test for the disorder; professionals make the diagnosis through the interpretation of behavior. There also is no cure, but children can be treated, according to Rebecca Landa, director of the Kennedy Krieger Institute's Center for Autism and Related Disorders and a contributor to the CDC report.

The greatest benefits of treatment occur when the children are young, and their brains are still developing and can be influenced more. But later therapy still can help, she said.

Landa said her research shows that children can be diagnosed at a year old, but only half of cases will show symptoms at that age. Children need to be screened again at age 3 and again later. In the CDC report, the median age of diagnosis was 5.6 years, though officials said more children were diagnosed by age 3 than in the past.

Autistic children consistently display social impairment, Landa said. They miss milestones, such as pointing at things that bring them joy, making eye contact or imitating acts they witness. As they age, they may not talk or develop proper methods of interaction with peers on schedule.

Landa said scientists agree that there are genetic and environmental factors playing a role in who develops autism. About 10 percent of cases can be explained by genetics alone. Others may be at risk due to a combination of genes and exposure to medications, or even lack of vitamins. Some researchers are exploring if pollution or certain pesticides play a role.