There are few solid things we know about autism spectrum disorder (ASD), maybe save that vaccines don't cause it. But a new report, released last week by the US Centres for Disease Control and Prevention, seems to reaffirm a long-standing pattern: The rate of autism diagnoses is continuing to increase.
Researchers from 11 US states enrolled in the Autism and Developmental Disabilities Monitoring (ADDM) network were brought together and asked to analyse the medical and school records of more than 300,000 children who were 8-years-old in 2014. They then confirmed diagnoses of autism using guidelines established by the current fifth edition of the Diagnostic and Statistical Manual of Mental Disorders, as well as the guidelines of the previous edition.
Combined, they estimated that about one in every 59 children had autism, a 15 per cent increase from the one in every 64 rate reported two years earlier. As has long been the case, boys were overwhelmingly more likely to be diagnosed with autism than girls, as were white children compared to black and Hispanic children.
On a state by state level, New Jersey's rate was the highest - one in every 34 children - while Arkansas had the lowest rate, at one in every 77 children. The other states included in the research were Arizona, Colorado, Georgia, Maryland, Minnesota, Missouri, North Carolina, Tennessee, and Wisconsin.
Estimated rates of autism have increased steadily over the decades, including since the CDC first began extensively tracking it in 2000. But after the 2016 report showed no significant jump from 2010 to 2012, officials hoped that rates had stabilised.
"It is now clear that what we saw in 2016 was just a pause along the way," said co-author Walter Zahorodny, an associate professor of pediatrics at Rutgers New Jersey Medical School who led the New Jersey team, in a statement. "It remains to be seen at what point ASD rates will plateau."
Why autism is seemingly becoming more common has been the subject of contentious debate.
From the fringes, antivaxxers have insisted the growing number of vaccines has sparked a new hidden plague. Mainstream researchers, on the other hand, have chalked up much of the increase to differences in how cases of autism are tracked and diagnosed as well as a greater awareness of its symptoms. The ADDM's numbers, for instance, are different than the rate detected by a study published earlier this January. That study, using data from a nationally representative survey of parents also regularly conducted by the government, estimated the autism rate to be one in every 41 children (the ADDM report is considered the official government estimate, however).
Many researchers, including Zahorodny, believe it's unlikely that the rise of autism cases can be chalked up to better diagnosing alone. But what combination of risk factors - which includes older parents, genetic mutations, and environmental toxins - is responsible for this increase is still a mystery.
"These are true influences that are exerting an effect, but they are not enough to explain the high rate of autism prevalence," said Zahorodny. "There are still undefined environmental risks which contribute to this significant increase, factors that could affect a child in its development in utero or related to birth complications or to the newborn period. We need more research into non-genetic triggers for autism."
The report also highlights how some things haven't changed much. The average age of confirmed diagnosis continues to hover around four-and-a-half-years-old. But it's well understood that the earlier someone's autism is detected, Zahorodny noted, the better off their outlook will ultimately be.
"Despite our greater awareness, we are not effective yet in early detection," he said. "Our goal should be systematic, universal screening that pediatricians and other health providers provide at regular visits starting at 18 months to identify ASD as soon as possible."
The symptoms of autism spectrum disorder, as the term suggests, vary from patient to patient, but can include problems with social interaction, learning, and communication as well as being unable to process sensations normally.