Thursday, 31 March 2016

The even newer CDC autism prevalence rate

"For 2012, the combined estimated prevalence of ASD [autism spectrum disorder] among the 11 ADDM [Autism and Developmental Disabilities Monitoring] Network sites was 14.6 per 1,000 (one in 68) children aged 8 years."

So said the report by Deborah Christensen and colleagues [1] continuing a research theme as the CDC map the estimated prevalence of autism in the United States over the years (see here and see here). This time around, as last time covering 2010, the figure settled on is an estimated 1 in 68 8-year olds; although boys were more readily diagnosed than girls (23.6 per 1000 vs. 5.3 per 1000 respectively, translating at 1 in 42 boys and 1 in 189 girls).

Eleven (states) sites brought data to bear in this study, and once again, New Jersey (NJ) came out top in terms of the prevalence estimates (1 in 41). The authors note that "both education and health care records were reviewed" in NJ whereas the site with the lowest prevalence rate, Maryland, only health care records were reviewed. It's also worthwhile noting that although the overall estimated figure for autism prevalence was the same as for the 2012 data, there were some interesting trends according to different sites. So: "Significantly increased ASD prevalence estimates were observed in New Jersey (12%) and Wisconsin (16%). In Missouri, estimated ASD prevalence decreased significantly, by 19%, and at the remaining five sites (Arizona, Colorado, Georgia, North Carolina, and Utah), ASD prevalence estimates did not change."

As per the press release accompanying the data, there were some significant disparities in terms of racial and ethnic groupings. "Estimated ASD prevalence was significantly higher among non-Hispanic white children aged 8 years (15.5 per 1,000) compared with non-Hispanic black children (13.2 per 1,000), and Hispanic (10.1 per 1,000) children aged 8 years." The authors speculate that this is probably less to do with Hispanic and non-Hispanic black racial groupings as being somehow protective of autism and more to do with various barriers to screening and assessment - "Targeted strategies are needed to increase awareness and identification of ASD in minority communities."

There is also the promise of some interesting times ahead for the CDC autism prevalence initiative. The authors make mention of the introduction of the new DSM-5 guidelines (see here) and a suggestion that: "Beginning with the 2014 surveillance year, the ADDM Network will be able to estimate ASD case status on the basis of both DSM-5 and DSM-IV-TR." That'll make for important reading no doubt given the history of DSM and autism (see here).

I'd encourage readers to have a good look at the Christensen paper and draw their own conclusions about the positives and negatives of the approach undertaken and data reported. I do think it is a little too early to talk about a 'plateau' in the autism rates given what we know about the variability of autism across different geographies (see here) and other issues (see here). The authors say as much: "Although the overall prevalence estimate is unchanged from surveillance year 2010, prevalence ranged widely across the ADDM Network and prevalence increases were reported at two sites, suggesting that it is premature to conclude that the rising prevalence of ASD observed during the first decade of the 21st century might be slowing."

Indeed irrespective of the similarity in figures for 2010 and 2012, an estimated 1 in 68 8-year old children with autism still represents a significant number of children.


[1] Christensen DL. et al. Prevalence and Characteristics of Autism Spectrum Disorder Among Children Aged 8 Years — Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2012. Morbidity and Mortality Weekly Report (MMWR). 2016; 65: 1-23.

---------- Christensen, D., Baio, J., Braun, K., Bilder, D., Charles, J., Constantino, J., Daniels, J., Durkin, M., Fitzgerald, R., Kurzius-Spencer, M., Lee, L., Pettygrove, S., Robinson, C., Schulz, E., Wells, C., Wingate, M., Zahorodny, W., & Yeargin-Allsopp, M. (2016). Prevalence and Characteristics of Autism Spectrum Disorder Among Children Aged 8 Years — Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2012 MMWR. Surveillance Summaries, 65 (3), 1-23 DOI: 10.15585/mmwr.ss6503a1