Autism diagnoses in NZ have more than tripled since 2009

New Zealand's autism rates have more than tripled in the last 15 years, with diagnoses continuing to rise in both children and adults, prompting a warning from researchers about the country's health and disability services needing to prepare for a continued growth in demand.

The findings come after a study from the University of Otago's faculty of medicine, which suggested there was no evidence of the increase slowing.

University of Otago department of psychological medicine associate professor Ben Beaglehole led the study, which analysed three national health and disability databases between 2009 and 2023.

The university said the study has created "the most comprehensive picture yet" of autistic spectrum disorder prevalence across the New Zealand population, and it was the first to examine autism diagnosis trends across children and adults in New Zealand.

More than 30,800 people with ASD were identified during the study period, with most diagnoses recorded through the national disability support database, which researchers said highlighted the increasing demand for disability services alongside health care.

Researchers found autism prevalence and the frequency of new diagnoses increased more than threefold during the study period.

By 2023, 1.3% of New Zealand children and 0.14% 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 but carried important implications for the country.

"While we've known autism diagnosis rates in children have been increasing, our study shows the same pattern is also occurring in adults, and we found no evidence the trend is beginning to plateau."

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. However, it is in fact a lifelong disorder, with demand likely to occur throughout the lifespan.

"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."

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

Researchers had also observed marked changes among Māori. They found diagnosis rates, initially lower than for non-Māori in 2009, increased almost fivefold and had overtaken non-Māori by 2023. Higher diagnosis rates were also observed in more socio economically deprived communities.

The study was not designed to identify why ASD diagnoses are increasing, but Beaglehole said the reason is likely to be complex.

"It's unlikely there's a single explanation. Increased awareness, broader diagnostic criteria, better access to assessment and changing patterns of healthcare use are all likely to be contributing. There may also be broader environmental and societal influences that we don't yet fully understand," he said.

The number of pre-school children being diagnosed with ASD had also been increasing. Researchers said this meant autism is being recognised earlier.

Adult diagnoses also continued to rise steadily, signalling many people were still being diagnosed later in life.

Beaglehole said the findings should prompt long-term planning across New Zealand's health and disability sectors.

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

Researchers concluded the increase in autism diagnoses were unlikely to be explained by genetic change alone, and instead suggested multiple interconnected social, environmental and healthcare factors contributing to the upward trend.

The study –Autism Spectrum Disorder trends for children and adults in New Zealand: a longitudinal examination of three national databases – has been published in The Australian and New Zealand Journal of Psychiatry.