The association of unipolar depression with thirty-day mortality after hospitalization for infection: A population-based cohort study in Denmark

OBJECTIVE: While depression is associated with higher risk of death due to chronic medical conditions, it is unknown if depression increases mortality following serious infections. We sought to determine if pre-existing unipolar depression is associated with increased mortality within 30days after hospitalization for a serious infection. METHODS: We conducted a population-based cohort study of all adults hospitalized for an infection in Denmark between 2005 and 2013. Pre-existing unipolar depression was ascertained via psychiatrist diagnoses or at least two antidepressant prescription redemptions within a six month period. Our primary outcome was all-cause mortality within 30days after infection-related hospitalization. We also studied death due to infection within 30days after admission. RESULTS: We identified 589,688 individuals who had a total of 703,158 hospitalizations for infections. After adjusting for demographics, infectious diagnosis and time since infection, socioeconomic factors and comorbidities, pre-existing unipolar depression was associated with slightly increased risk of all-cause mortality within 30days after infection-related hospitalization (Mortality Rate Ratio [MRR]: 1.07, 95% Confidence Interval [95% CI]: 1.05, 1.09). The association was strongest among persons who initiated antidepressant treatment within one year before the infection (MRR: 1.30, 95% CI: 1.25, 1.35). Pre-existing unipolar depression was associated with increased risk of death due to sepsis (MRR: 1.30, 95% CI: 1.17, 1.44), pneumonia (MRR: 1.23, 95% CI: 1.16, 1.29) and urinary tract infection (MRR: 1.25, 95% CI: 1.08, 1.44) after adjusting for demographics, infectious diagnosis at admission and time since infection. CONCLUSIONS: Pre-existing unipolar depression is associated with slightly increased mortality following hospitalization for an infection.