Less than 3% of Australian children diagnosed with autism spectrum disorder are being identified by the age of 2, the earliest age ASD can be reliably diagnosed, according to research published in the Medical Journal of Australia.
Researchers from La Trobe University found that the average age of diagnosis for the 15 074 children aged under 7 registered with the Helping Children with Autism Package (HCWAP) between 30 June 2010 and 30 June 2012 was 4 years and 1 month.
The researchers, Ms Catherine Bent, a PhD candidate at La Trobe working under the supervision of Prof. Cheryl Dissanayake and Dr Josephie Barbaro, wrote that "this finding represents a possible average delay [in diagnosis] of 2 years (and common delays of up to 4 years)".
Children registered with the HCWAP in Western Australia and New South Wales were diagnosed earlier (median age at diagnosis of 3 years and 10 months, and 3 years and 11 months, respectively) than in other states. Girls registered with HCWAP were diagnosed an average of 1 month earlier than boys.
There was no significant difference in diagnosis age between Indigenous children and non-Indigenous children, although children from a culturally and linguistically diverse background were diagnosed 5 months earlier than other children.
The most frequent age of diagnosis found in the study was 5 years and 11 months.
"The increase in frequency of ASD diagnoses at 6 years of age may be attributable to children's ASD being identified when they enter school, aged about 5 years, and the associated delay for diagnostic assessments", the authors wrote.
"The end of the eligibility period for funding through the HCWAP (at age 7) may also contribute to the increase in diagnoses at 6 years of age.
"Further, there may be a subgroup of children who are diagnosed later because of factors in their clinical presentation, such as comorbid conditions or the presentation being less severe."
The researchers report that the incidence of ASD in Australia has been steadily rising. In 1999-2000 the incidence of ASD in 0-4-year-olds was 5.1 per 10 000 in NSW and 8.0 per 10 000 in WA, whereas from 2003 to 2005 the national prevalence in 0-5-year-olds was estimated to increase from 16.1 to 22.0 per 10 000.
However, their study reports that more than three times this number are currently diagnosed with ASD and registered with the HCWAP. Several factors may be contributing to this, such as increased awareness and changes to the diagnostic criteria.