New Jersey preschoolers have the highest rates of autism ever measured in the United States, a rate that has increased faster than in other states studied, researchers at Rutgers University reported Thursday. The rate of autism among children here has tripled in a generation.

One in 35 children in New Jersey was diagnosed with autism by their 4th birthday, according to the study published by the federal Centers for Disease Control on Thursday. Those children were more likely to have attracted the attention of pediatricians and early-childhood educators because of moderate to severe symptoms of autism. Still more children are diagnosed with autism when they enter public schools.

The relentless climb in autism rates — from 1% of children born in 1992 to 3% of children born in 2010 — has shown no signs of reaching a plateau, said Walter Zahorodny, an associate professor at Rutgers New Jersey Medical School who directed the New Jersey portion of the study.

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"The explosive rate of autism is impossible to ignore," he said. School districts face increasing demand for educational resources for children with autism. Clinicians face long waiting lists for their services. "There's no letup," he said. "I really don't understand why the rate is going up in this way."

Researchers can’t explain why autism rates have increased in New Jersey and elsewhere.

Contributing factors include genetic mutations and birth-related risks, such as being born prematurely, as one of a multiple birth, to a mother who was ill during pregnancy or to parents who are older than 30. But the greatest influences appear to be unknown environmental factors, Zahorodny said.

Among 4-year-olds, the rate climbed 43 percent in just four years, from 2010 to 2014, he said. One in 23 4-year-old boys in New Jersey is now diagnosed with autism.

"We must take swift and systematic action to increase access to and fund medically necessary treatment for every child with autism," said Suzanne Buchanan, executive director of Autism New Jersey. "Early identification is crucial to helping families access services for these preschoolers, who need intensive treatment to learn developmentally appropriate skills and maximize their potential."

The New Jersey data is included in a seven-state study by the Early Autism and Developmental Disabilities Monitoring Network, which has monitored rates of autism diagnoses for 19 years. Researchers in Arizona, Colorado, Missouri, North Carolina, Utah and Wisconsin, as well as New Jersey, screened the health records of nearly 71,000 children. Three states used education records in addition to health records.

In all, they identified more than 1,200 children with autism. The New Jersey study included every 4-year-old in Essex and Union counties — 18,112 children in 2014 — and identified 514 with autism.

Boys in New Jersey were 3½ times more likely than girls to be diagnosed with the disorder, the data showed. Autism diagnoses among whites, blacks and Hispanic children increased at the same rate, although white children were slightly more likely to be diagnosed.

Perhaps most disturbing: The age at first diagnosis didn't budge in 15 years.

In New Jersey, it even increased by a few months — perhaps because the growing demand for services and the limited number of providers meant delays in care, Zahorodny said.

“Despite our greater awareness, we are not effective yet in early detection,” he said. “Our goal should be systematic, universal screening" by pediatricians and other health providers at regular visits from 18 months of age onward.

Autism is a complex disorder that interferes with social interaction and communication. People with autism display a range, or spectrum, of behaviors from obsessive interest in certain subjects and repetitive speech patterns to self-injurious behavior with little or no ability to communicate. The development of a child's brain is affected early in life, and while there is no cure, early intervention can maximize a child's ability to function and participate in the community.

Across the country, rates of autism ranged from a low of 8 per 1,000 children in Missouri to New Jersey's high of 28 per 1,000 children. The national average was 13 per 1,000 children, according to the study.

"The experience of our special education system and the number of developmental specialists in our region" meant New Jersey's data was probably more complete than that of other states, Zahorodny said. States with lower rates probably had not identified all those affected, he said.