Multimorbidity and vulnerability among those living with psychosis in Indigenous populations in Cape York and the Torres Strait.

Objective: Previous research has found an alarmingly high rate of psychosis in Indigenous patients from remote communities of Cape York and the Torres Strait with the treated prevalence of psychosis four times higher than that found for the Australian population. This study assesses comorbid illness and risk factors among this same cohort of psychosis patients.

Methods: Data were collated from a clinical database that contains complete psychiatric records from 1992 to 2015, extracted for all Indigenous patients who received treatment for a psychotic disorder from the Remote Area Mental Health Service. Descriptive analysis and logistic regression models explored differences across subgroups of ethnicity and sex, and relationships between co-morbid disorders and risk factors. All multivariate models included variables of age, year of birth, sex and ethnicity.

Results: Sixty per cent of participants ( = 256) experienced a comorbid mental or substance use disorder. Forty-five per cent ( = 192) of participants experienced a physical comorbidity. The most frequent physical health outcomes were injury (29%,  = 93), diabetes (18%,  = 58) and cardiovascular disease (21%,  = 68). Risk factors considered to play a potential biological or neurodevelopmental role in the development of psychosis were approximately three times more likely in Aboriginal (odds ratio = 3.2; 95% confidence interval = [2.0, 4.9]) versus Torres Strait Islander patients, and those born after 1980 (odds ratio = 2.5; 95% confidence interval = [1.6, 3.9]) versus those born prior to 1980. Environmental or contextual factors were associated with significantly greater risk among Aboriginal (odds ratio = 3.8; 95% confidence interval = [2.4, 6.0]) compared with Torres Strait Islander patients.

Conclusion: Our data expose the perinatal and early environment of Indigenous children who later developed a psychotic disorder. As risk factors for schizophrenia may be cumulative and interactive, both with each other and with critical periods of neurodevelopmental vulnerability, our results suggest possible causes for the increasing prevalence of psychotic disorders between 1992 and 2015.