If you were to believe newspaper reports and anecdotal evidence about autism, you probably think rates of the disorder are exploding around the world.
But a recent study — the most extensive review of the data on the global prevalence and incidence of autism, published in the journal Psychological Medicine — actually found rates have remained unchanged since 1990.
"This study drew together research findings on autism spectrum disorders conducted across the world over the past 20 years," says study lead Amanda Baxter.
7.5 per 1,000 had autism in 1990; 7.6 per 1,000 had it in 2010
Studies using different methods and sample sizes reported a range of prevalence estimates, though few actually reported an increase. When Baxter and her co-authors adjusted for differences in the study methods and synthesized the results, they found no evidence for a growth in the prevalence of autism spectrum disorders over time and little regional variation.
"In 2010 there were an estimated 52 million cases of (autism spectrum disorders) around the world, equating to a population prevalence of 7.6 per 1000 or one in 132 persons," the study authors wrote. "In 1990, age-standardized point prevalence for ASDs was 7.5 per 1000 compared with 7.6 per 1000 in 2010."
Autism spectrum disorders include autism, Asperger syndrome, and "pervasive developmental disorder, not otherwise specified" commonly known as PDD-NOS. All of these neurodevelopmental disorders impair people's ability to communicate and interact socially. Their cause is still not known.
When asked about the reports on rising rates of autism disorders in the US and other countries, Baxter says those are mostly explained by an increase in awareness and diagnosis.
"Reports of higher rates of autism in recent years means that we are doing a better job of identifying people on the autism disorder spectrum, particularly those at the milder end of the spectrum, and also identifying them at an earlier age."
What's more, autism spectrum disorders — which causes social impairment and stifles people's ability to communicate — still represents significant suffering globally. "The burden of disease caused by the disorders is not only high in children but continues throughout the lifespan into adulthood," says Baxter. "In 2010, autism spectrum disorders caused 7.7 million person-years of healthy life lost, around the world."
The researchers also found a "huge gap" in the data about adults with autism. "Only one study has been conducted on autism spectrum disorders in adults," she says. So even if rates aren't sky-rocketing, there's still a lot of room for understanding.