Autism diagnoses more than tripled in 15 years - study

A study has found diagnoses of autism spectrum disorder (ASD) in New Zealand have more than tripled in 15 years.

The Otago University researchers warn the country's health and disability services will need to prepare for a continued growth in demand, as there's no evidence the increase is slowing.

Published in The Australian and New Zealand Journal of Psychiatry, the study is the first to examine autism diagnosis trends across New Zealand children and adults.

Led by Associate Professor Ben Beaglehole from Otago's Department of Psychological Medicine, the research analysed three national health and disability databases between 2009-23 and found a more-than-threefold increase.

More than 30,800 people with ASD were identified during the study period.

By 2023, 1.3 percent of New Zealand children and 0.14 per cent of adults had an ASD diagnosis recorded in national databases, with increases recorded across all age groups, genders and ethnicities.

Beaglehole said the findings reflected international trends.

The big question - why?

While the study was not designed to identify why ASD diagnoses were increasing, Beaglehole said there was unlikely to be a single explanation.

It could be due to increased awareness, broader diagnostic criteria, better access to assessment and changing patterns of healthcare.

"There may also be broader environmental and societal influences that we don't yet fully understand," he said.

The researchers concluded it was unlikely to be explained by genetic change alone - rather, they suggested interconnected social, environmental and healthcare factors contributed.

The research also found more pre-school children were being diagnosed, suggesting autism was being recognised earlier.

"Our results suggest increasing demand for autism-related services is likely to continue," Beaglehole said. "That means investing in workforce training, improving service planning, and ensuring both child and adult services are equipped to provide appropriate care."

It's not just a childhood condition

Beaglehole said one of the study's most significant findings was the continuing rise in adult diagnoses.

"Autism has traditionally been viewed as a childhood condition from a research perspective," he said. "However, it is in fact a lifelong disorder."

"We're also seeing adults who are receiving a diagnosis later in life. That means adult health services need to build greater expertise and capacity to support this growing population."

It remained more common among males, although diagnoses among females had increased at a faster rate than males over the 15-year period.

Researchers also observed marked changes among Māori. Initially lower than for non-Māori in 2009, diagnosis rates increased almost fivefold and had overtaken non-Māori by 2023.

Higher diagnosis rates were also seen in more socio-economically deprived communities.