More than half a million U.S. children have autism, with costly health care needs that often put an unprecedented financial strain on their families, national data show.

Compared with parents whose youngsters have chronic health care needs but not autism, those with autistic children are three times more likely to have to quit their jobs or reduce work hours to care for their kids. They pay more for their kids’ health needs, spend more time providing or arranging for that care, and are more likely to have money difficulties, the study found.

“This is the first national survey that looked at the impact on families of having kids with special health care needs,” said lead author Michael Kogan, a researcher with the government’s Maternal and Child Health Bureau.

The results are from a nationally representative 2005-06 survey of nearly 40,000 children with special health care needs. These children have a broad range of chronic conditions, including physical and mental illness, requiring more extensive than usual medical care.

A total of 2,088 children with special health needs had autism, which translates to about 535,000 kids aged 3 to 17 nationwide, the study authors said.

The study appears in the December 2008 issue of Pediatrics.

Autism typically involves poor verbal communication, repetitive behaviors such as head-banging, and avoidance of physical or eye contact. Affected children often need many more types of treatment than kids with other chronic conditions, including speech and behavior therapy and sometimes medication. Kogan said that might explain the disproportionate strain on their families.

Jacquie Mace, whose 12-year-old son, Austin, has autism, said the study presents a “very realistic” picture of the challenges affected families face.