Infections during brain development appear to contribute to cognitive impairment and aggressive behavior, as well as to a number of developmental mental disorders closely associated with violent criminal behavior. Yet, no study has thus far ever investigated whether infections during brain development increases the risk of violent criminality later in life.

In this population-based cohort study, about 2.2 million individuals born in Sweden between the years 1973 and 1995 were included in an effort to estimate the association between infections during childhood (registered ICD-10 diagnoses of infections incurred before the age of 14 years) and violent criminal behavior (registered convictions for a violent crime between the ages of 15 and 38 years, prior to December 31, 2011). After inclusion of several sociodemographic parameters, risks of violent criminal behavior conferred by childhood infections – expressed as hazard ratios (HRs) and 95% confidence intervals (CIs) – were calculated by means of Cox regression. Mediation analyses were performed to explore the effect of psychiatric disorders on the association between infections during childhood and violent criminality. Results revealed a modest, yet significant, association between an infection during childhood and violent criminality later in life (adjusted HR 1.14, 95% CI 1.12–1.16). Infections during the first year of life and infections in the central nervous system were associated with the highest risks of subsequent violent criminality (adjusted HR 1.20, 95% CI 1.18–1.23, and adjusted HR 1.17, 95% CI 1.08–1.26, respectively). The association was partly mediated by the presence of a psychiatric disorder.

In summary, independent of a wide range of covariates, our results suggest that infections during brain development could be part of the genesis of violent criminal behavior.