Researchers attributed highest autism rates yet to better detection

Among U.S. children, 110 of every 10,000 have autism, new estimates from a nationally representative study indicated — a sharp increase from the two to five per 10,000 reported from the 1960s to the 1980s and the 30 to 60 per 10,000 reported in the earlier part of this decade.

“Methodologic changes between the surveys (with the inclusion of Asperger’s disorder, pervasive developmental disorder and other autism spectrum disorders [ASD]) and overall increases in public awareness and provider identification of ASD might partly explain the increased prevalence,” wrote researchers from the Department of Health and Human Services and Harvard Medical School.

Younger average age at diagnosis, more widely available diagnostic services, greater public awareness and growing acceptance of autism as a co-condition with other developmental disorders were among additional factors the researchers said may help explain the increases in prevalence.

Calculations were based on data from the 2007 National Survey of Children’s Health, a random digit–dial telephone survey involving information from 78,037 children aged 3 to 17 years. Using weighted point-prevalence models based on parent-reported data, the researchers estimated that 673,000 U.S. children currently have ASD.

ASD in the sample population was most often described as mild (49.6%), followed by moderate (33.9%) and severe (16.5%). Parental education was the only significant predictor of severity; parents with less than 12 years of education were more likely to rate their child’s autism as moderate or severe (68%) compared with parents who had more education (43.5%).

Findings also confirmed previously reported trends including four times greater odds for ASD among boys compared with girls and a higher likelihood of ASD diagnosis among non-Hispanic white children compared with non-Hispanic black and multiracial children.

Researchers also determined that 40% of children whose parents reported that their child received a previous ASD diagnosis did not currently have the disorder. Possible explanations for the discrepancy included initial misdiagnosis on the basis of mental retardation or another learning disability and suspected ASD that was later ruled out.

Because parent-reported ASD was never confirmed by external sources, another possibility is that some parents with children who meet current criteria for the disorder may have responded “no” because their child did not receive special services, according to the researchers.

“This may be driven by the unique circumstances of ASD, which require treatment and coordination among an unusually large number of health and other disciplines, including primary care, educational, rehabilitation and behavioral health services,” the researchers wrote.

“Further understanding of the groups at highest risk for being diagnosed with ASD and the factors associated with current ASD symptoms, severity and health care impact could lead to more effective interventions.”

Kogan MD. Pediatrics. 2009;124:1-9.