Prevalence of psychiatric conditions in people with intellectual disability: A record linkage study in New South Wales, Australia

Objective: To compare the prevalence of psychiatric conditions in a population-based cohort of people with intellectual disability and matched comparators in New South Wales, Australia. Method: The study cohort included 97,644 people with intellectual disability and 451,502 comparators aged ⩾ 5 between 1 July 2001 to 30 June 2018. We used linked records of hospital admissions, emergency department presentations, ambulatory mental health service contacts, and Medicare rebates to identify any, serious, and specific psychiatric conditions. Results: People with intellectual disability showed greatly elevated period prevalence of any psychiatric condition (76.0% vs 38.3%), serious mental illness (16.2% vs 5.1%), and all specific psychiatric conditions compared to comparators. Among people with intellectual disability and congenital/developmental conditions, people with Down syndrome showed reduced risk of most psychiatric conditions while people with attention-deficit hyperactivity disorder and people with learning disorders showed increased risk. Age-specific analysis showed earlier onset of dementia and heightened prevalence of self-injury/suicidality in adulthood among people with intellectual disability. Annualised prevalence trends showed increases in 2006–2007 for most psychiatric conditions and decreases in 2014–2015 to 2017–2018. Conclusions: The higher prevalence of psychiatric conditions in people with intellectual disability indicates the importance of systemic responses to address the mental health needs of this population. Our findings highlight the importance of considering the psychiatric profiles of specific congenital/developmental conditions among people with intellectual disability, and the need to provide targeted services to high-risk groups such as those with co-occurring attention-deficit hyperactivity disorder.