May 4, 2011— -- Is autism a growing epidemic or not? Recent reports have suggested that autism is on the rise, but a new study from the U.K. finds that the prevalence of this developmental disorder has remained stable. It may be that doctors are diagnosing it more often in young people -- not that it's actually happening more.
Researchers performed clinical assessments of 618 adults and found that nearly 1 percent of Britons over age 16 suffered from autism -- meaning the adult rate is no higher than that seen among children in the U.K.
"If the rate of autism is actually increasing rapidly, you'd expect rates to be much lower in older adults, but we didn't find that," says Dr. Traolach Brugha, lead author on the study and psychiatrist at the University of Leicester, U.K. "We found similar rates at 16 up to the 70s and 80s. That suggests that the number of people developing the condition have not changed over the last seventy or eighty years."
Though this study deals with the U.K. population, these findings call into questions whether the much-discussed "autism epidemic" in the U.S. is a real phenomenon.
"It has never been fully clear whether the much increased rate of autism over the past few decades is due to increased recognition…or whether there has been a genuine increase. This study suggests that there is no true increase," says Dr. Shlomo Shinnar, professor of neurology and pediatrics at Montefiore Medical Center in New York.
Because the U.K. and the U.S. have similar rates of autism in children (about 1 percent), these U.K. findings speak to the autism debate in the states as well, says Shinnar. "The fact that similar rates of 1 percent are being seen in the adult population when screened is a strong indication that these results are highly relevant to the U.S. as well."
Fears of an autism epidemic were sparked in 2009 when the Centers for Disease Control and Prevention reported that the rate of autism in children had increased 57 percent since 2002. The most recent data puts the prevalence of autism in children the U.S. at about 1 in 100 -- a similar rate to that found in the U.K. population.
"The CDC studies are showing that the rate of diagnosis has increased," not necessarily the actual number of cases, says Brugha. "What we found is that there is a very low level of recognition of autism in adults, which means that rates may not be increasing, people may just be better at recognizing it."
Autism is still under-recognized in older children, adolescents and adults, says Dr. Nancy Minshew, Director of the NICHD Collaborative Program of Excellence in Autism at the University of Pittsburgh. These older patients "follow a downhill path because the basis of their 'behavior problems' is not correctly understood," she says.
The U.K. findings aren't necessarily surprising to those like Minshew who have studied autism for many years. Because the disorder went largely unpublicized until recently, it is to be expected that there would be a spike in diagnoses once public awareness of autism and other disorders on the autism spectrum increased.
"This is another example where urban myths and urban logic were allowed to dictate public thinking and press coverage, and finally science is bringing up the rear. It takes much longer to demonstrate science than to toss out conjecture," says Minshew.
The study was published in the May issue of Archives of General Psychiatry.