BACKGROUND: Evidence links infections to mental disorders and suicidal behavior. However, knowledge is sparse regarding less severe infections, anti-infective treatment, and deliberate self-harm. Using nationwide Danish longitudinal registers, we estimated associations between infections treated with anti-infective agents and infections requiring hospitalization with the risk of deliberate self-harm.

METHODS: A total of 1.3 million people born between 1977 and 2002 were followed during the period from 1995 to 2013. In total, 15,042 individuals were recorded with deliberate self-harm (92% had been treated with anti-infective agents and 19% had been hospitalized for infections) and 114 died by suicide (64% had been treated with anti-infective agents and 13% had been hospitalized for infections). Hazard rate ratios were obtained while adjusting for age, gender, calendar period, education, hospitalizations with infections, prescribed anti-infective agents during childhood, parental mental disorders, and parental deliberate self-harm.

RESULTS: Individuals with infections treated with anti-infective agents had an increased risk of deliberate self-harm with a hazard rate ratio of 1.80 (95% confidence interval = 1.68-1.91). The associations fitted a dose-response relationship (p < .001) and remained significant up to 5 years after last infection. An additive effect was found for individuals with an additional hospitalization for infections with an increased hazard rate ratio of 3.20 (95% confidence interval = 2.96-3.45) for deliberate self-harm.

CONCLUSIONS: An increased risk of deliberate self-harm was found among individuals with infections treated with anti-infective agents in temporal and dose-response associations. These results add to the growing literature on a possible link between infections and the pathophysiological mechanisms of suicidal behavior.