Prevalence and Incidence in the UK and US

At BMJ Open, Brent Taylor, Hershel Jick, Dean MacLaughlin have an article titled "Prevalence and Incidence Rates of Autism in the UK: Time Trend from 2004–2010 in Children Aged 8 Years.".  The abstract:

Objectives To update UK studies begun in the early 1990s on the annual prevalence and incidence rates of autism in children; undertaken in response to a March 2012 press release, widely covered by the media, from the US Centre for Disease Control (CDC) reporting that the autism prevalence rate in 2008 in 8-year-old US children was 1 in 88, a 78% increase from a CDC estimate in 2004. This finding suggested a continuation of the dramatic increase in children diagnosed as autistic, which occurred in the 1990s.

Design Population study using the UK General Practice Research Database (GPRD).

Methods Annual autism prevalence rates were estimated for children aged 8 years in 2004–2010 by dividing the number diagnosed as autistic in each or any previous year by the number of children active in the study population that year. We also calculated annual incidence rates for children aged 2–8 years, by dividing the number newly diagnosed in 2004–2010 by the same denominators.

Results Annual prevalence rates for each year were steady at approximately 3.8/1000 boys and 0.8/1000 girls. Annual incidence rates each year were also steady at about 1.2/1000 boys and 0.2/1000 girls.

Conclusions Following a fivefold increase in the annual incidence rates of autism during the 1990s in the UK, the incidence and prevalence rates in 8-year-old children reached a plateau in the early 2000s and remained steady through 2010. Whether prevalence rates have increased from the early 2000s in the USA remains uncertain.

Autism Speaks reports:

“In the US, part of the increase in prevalence has been from increased detection, especially among ethnic minorities,” comments epidemiologist Michael Rosanoff, Autism Speaks associate director for public health research. “Disparities in access to autism services and differences in healthcare systems may be additional factors behind reported differences between countries.” Autism Speaks’ Early Access to Care and Global Autism Public Health initiatives continue to address these gaps in access to services in underserved communities.

In addition, the rate at which autism prevalence is increasing has slowed in the US over the last decade, Rosanoff notes. “While we saw a 57 percent increase between 2002 and 2006, the increase from 2006 to 2008 was only 23 percent,” he says. “We will see if this trend continues when the CDC releases new numbers.”

Finally, the US approach to estimating autism prevalence may be more comprehensive than that of the UK study. The Centers for Disease Control and Prevention (CDC) uses both medical and school records from multiple sources to detect cases. The British researchers based their estimates solely on medical records from the UK’s General Practice Research Database.