Incidence Rates and Risk of Hospital Registered Infections among Schizophrenia Patients before and after Onset of Illness: A Population-Based Nationwide Register Study

Infections in schizophrenia patients are associated with an increased premature mortality. However, our knowledge about the burden of infections in schizophrenia is scarce. The aims of this study were to (1) determine the prevalence of clinically important hospital registered infections in the period of five years prior to and five years after the diagnosis, (2) estimate the risk of infections before and after the schizophrenia diagnosis and, (3) evaluate the impact of comorbidity on the risk of infections in schizophrenia. Using combined data from Danish national registers, we sampled a cohort of all persons born in Denmark in the period 1975–1990 and obtained health-related records from 1995–2013. Occurrence patterns and the risk of infections were measured as annual incidence rates and incidence rates ratios, estimated using Poisson models. Medical conditions from the Charlson Index were considered as a measure of comorbidity. The analyses showed that schizophrenia patients had a significantly elevated risk of almost all types of hospital registered infections during the period of the study when compared to the controls. Comorbidity increased rates of infections by 176%. The results suggest that the risk of infections is elevated in the schizophrenia population and physical illness is an important risk factor.