Background: People who have been diagnosed with schizophrenia are known to be at increased risk of suicide. However, the increased risk is usually expressed by the cumulative or lifetime incidence of completed suicide in people diagnosed with schizophrenia. What is more useful in informing priorities and designing suicide prevention strategies is to know what proportion of completed suicides are by people diagnosed with schizophrenia. Most studies that report on this figure use small samples from selected populations. We aimed to use data on all deaths from the population of Ontario, Canada over nine years to estimate what proportion of suicide deaths occurred in people diagnosed with schizophrenia.
Methods: Using population health administrative data from Ontario, we performed a population study of all deaths from January 1st, 2000 to December 31st 2018. We identified all deaths which were recorded as suicides. People diagnosed with schizophrenia were identified using a validated case definition based on the presence of three or more outpatient physician claims for schizophrenia within three years or one or more hospital discharge records (from general acute or psychiatric hospitalizations) with a diagnosis of schizophrenia over their lifetime. We excluded those under the age of 18, non-Ontario residents and people who were not eligible for provincial health insurance.
Results: The cohort included 954,028 adults who had died over nine years, of whom 10643 had died by suicide. Of these suicides, 1052 (9.9%) were in people who had been diagnosed with schizophrenia. In this group, the mean age at death was 44, with a third being female and two-thirds male. Forty percent of these suicide deaths occurred within 5 years of diagnosis, and nearly 40% were from the most deprived population quintile.
Conclusions: One in ten people who die by suicide in Ontario has been diagnosed with schizophrenia. Given that this is a population that is known to health care services and often in treatment this should be a priority population for suicide prevention efforts. However, they are often ignored in suicide prevention strategies and rarely discussed in suicide prevention forums therefore reinforcing existing inequities.