A new study finds that the reported prevalence of autism has leveled off in the United Kingdom since 2004, after skyrocketing five-fold in the 1990s as it did in the United States. This contrasts with a 78 percent increase in autism’s estimated prevalence in the United States between 2002 and 2008.
The UK report appears today in the online journal BMJ Open. The authors, from University College London, say their results raise uncertainties about recent increases in autism’s global prevalence and whether they will continue.
What accounts for the difference?
“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.
Contrasts and parallels in numbers
Like the CDC, the British researchers looked at 8 year olds to calculate autism prevalence. They found that the number in the UK remained flat between 2004 and 2010 – at around 1 in 250 boys and just under 1 in 1,000 girls.
This is substantially lower than the CDC’s most recent estimate of 1 in 54 boys and 1 in 252 girls. It is also lower than some UK studies that used different approaches to identify autism.
The UK researchers note that their own previous research documented a five-fold rise in autism prevalence over the course of the 1990s. This parallels the increase seen in the US during that time period. Increased awareness and a broadening of diagnoses only partially explain that rise, they say. Researchers still know little about the factors that may play a role in the increased prevalence.
“What we do know is that millions are affected and many are still being missed,” Rosanoff concludes.