The disorder now affects roughly 1.2 million children and teens in the United States. The report also highlights autism is almost five times more common among boys than girls.
The CDC says the findings don't mean more children are developing autism, it means more cases are being discovered due to heightened awareness.
Michael Rosanoff, with the advocacy group Autism Speaks, says this study looked at cases of 8 years old from 11 sites across the country,
"The approach that the CDC uses is based on medical and service records. So that is why we believe part of the increase in prevalence is due to better detection of autism. Better records and more records lead to higher prevalence."
Boys are still more likely to be diagnosed with an autism spectrum disorder than girls. White are also more likely to be diagnosed than African-Americans or Hispanics.
Diagnoses varied widely across the country, ranging from 1 in 175 in Alabama to 1 in 45 in New Jersey.
Rosanoff says the reason for the variation is "not because there is additional risk of autism in certain states, it's because there are more and better quality records in some states than others."
The CDC states the 30% jump in the past 2 years was not due to over diagnosis, and say their clinicians used standard definitions of autism to evaluate each diagnosis.
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