U.S. stats show autism rate reaching possible plateau

After years on the rise, the rate of autism among U.S. children may be leveling off.

According to data released today by the U.S. Centers for Disease Control and Prevention (CDC), 1 in 68 school-age children have the condition. The agency reported the same rate two years ago, hinting at a possible plateau in autism prevalence.

The new numbers come from a 2012 survey by the CDC’s Autism and Developmental Disabilities Monitoring Network, which tracks the number of children diagnosed with autism in 11 communities across the country. The agency launched the network in 2000, when it estimated a prevalence of 1 in 150. Since then, the rate has risen steadily, sparking fears of an ‘autism epidemic.’ Several studies have hinted that the rise in autism stems from increased awareness of the condition and diagnostic changes, however.

But the CDC cautions that it is too soon to tell whether the rate has stabilized.

“These are just two data points, and we’d like to see a few more to tell whether the rate is increasing, decreasing or staying the same,” says lead researcher Daisy Christensen, an epidemiologist at the CDC.

Prevalence estimates vary widely among the 11 communities, making it difficult to draw firm conclusions from the data. For instance, the surveillance site in New Jersey identified 800 children with autism, leading to a 1 in 41 prevalence estimate. The site in Maryland, by contrast, identified only 148 children with autism, yielding a prevalence of 1 in 123.

These discrepancies may also reflect the regions’ varying ability to identify autism cases in surveys, however, rather than a real difference in prevalence, experts say.

For example, the 2012 CDC survey showed a fourfold greater prevalence in Alabama versus Utah. “Nobody interprets these site differences as differences in incidence,” Eric Fombonne told Spectrum at the time. “It’s a difference in ascertainment.”

The differences are not only geographic. Within the same community, white children are more likely than black or Hispanic children to be identified with autism.

“We don’t have any evidence that these groups have a lower risk, so it may mean that some children aren’t being identified,” says Christensen. “Understanding that nonwhite children are less likely to be identified helps us direct efforts toward those communities to increase autism awareness.”

If the rate of autism truly is stabilizing, it could help to guide research into risk factors for the condition, Christensen says. Studies have hinted, for instance, that increasing parental age may be contributing to changes in prevalence. “Prevalence studies alone won’t be able to explain the causes of autism, but they can provide clues,” she says.

Interestingly, despite the changing rate in autism, the ratio of boys to girls with the condition has remained the same at roughly 4.5 to 1. “It’s one of the most stable findings we’ve seen,” Christensen says. “And that is fascinating. It gives some direction to researchers in terms of trying to get at whether there’s a protective factor for girls or a risk factor for boys.”

It is unclear how the new estimate stacks up against other measures of autism prevalence. Late last year, the CDC reported that 1 in 45 children have autism, based on an annual door-to-door survey.