A study published online by JAMA Psychiatry of patients in Sweden suggests trigger events, including exposure to violence, were associated with increased risk of violent crime in the week following exposure among patients with schizophrenia and bipolar disorder and among individuals without psychiatric diagnoses who were included for comparison.

Patients diagnosed with schizophrenia spectrum and bipolar disorders have higher rates of criminal convictions than the general population. The identification of triggers for violence could be potentially important for risk assessment. But there is a lack of evidence of triggers for violence in patients with psychosis.

Professor Seena Fazel, of the University of Oxford, United Kingdom, and coauthors used nationwide Swedish data for individuals born between 1958 and 1988 to examine a range of triggers for violent acts in patients with psychotic disorders and individuals without a psychiatric diagnosis.

The study sample included more than 2.8 million people – 34,903 patients with schizophrenia spectrum disorders, 29,692 patients with bipolar disorder and more than 2.7 million unaffected control individuals for comparison. The study examined six triggers: exposure to violence, parental bereavement, self-harm, traumatic brain injury, unintentional injuries and substance intoxication.

Absolute risks (the incidence in a population) for violent crime in the week following exposure to a trigger were typically highest among individuals diagnosed with schizophrenia, followed by those with bipolar disorder and then control participants who did not have psychiatric diagnoses, according to the results. Exposure to violence contributed to the largest absolute risks of a violent offence in the week following exposure to the trigger.

Relative risks (a ratio of the risk of those exposed to a trigger to the risk of those not exposed) were generally similar across the three groups for most triggers, according to the study.

The authors noted several limitations, including that other factors might explain exposure to triggers and violent crime.

'These findings support the hypothesis that recent exposure to a stressful life event, an intentional or unintentional injury, or having been diagnosed with substance intoxication increases the short-term risk of interpersonal violence in individuals with psychotic disorders and in controls,' the study concludes.