CHICAGO, May 2 (Xinhua) -- New statistics indicate that rates of autism in children in the United States have continued to increase, but have increased only modestly, suggesting there may be a leveling off.

Moreover, researchers found that many children aren't getting diagnosed until age four or older. The older a child is diagnosed, the harder it is for health-care professionals to intervene and change the trajectory of autism spectrum disorder.

The new statistical findings, from the 11-center Autism and Developmental Disabilities Monitoring Network which includes Washington University School of Medicine in St. Louis, are based on data from more than 10,886 children.

In 2014, the most recent year for which comprehensive statistics are available, researchers found that 1.7 percent of eight-year-olds, or 1 in 59, in the study had a diagnosis of autism spectrum disorder, as against 1.5 percent, or 1 in 68, in 2012.

This increase indicates an improvement in the identification of autism spectrum disorder, particularly in previously underdiagnosed minority populations, among other factors.

Some 39 percent of the children in the study who were diagnosed with an autism spectrum disorder didn't receive such a diagnosis until they were over 4 years of age, said John N. Constantino, a study author and professor of psychiatry and pediatrics at Washington University.

"It remains a priority to diagnose autism earlier and begin intervention sooner, especially given recent research suggesting that higher intensity and duration of early developmental therapy for children with autism is associated with significant improvements in outcomes," he said.

A higher percentage of white children than African-American and Hispanic children were identified as having autism spectrum disorder. That gap, however, is narrowing, which may be due in part to increased efforts to diagnosis children in minority communities.

Despite the narrowing gap, minority children with autism are disproportionately affected by intellectual disabilities related to the disorder. Some 44 percent of African-American children with autism also have intellectual disabilities, compared with 22 percent of white children with the disorder.

The findings were published April 27 in the Centers for Disease Control and Prevention's "Morbidity and Mortality Weekly Report."