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

• We studied if depression raised risk of 30-day mortality after serious infection.
• Depression raised risk of 30-day mortality after serious infection slightly.
• Persons starting antidepressants within a year pre-infection were at greatest risk.

ObjectiveWhile 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 30 days after hospitalization for a serious infection.MethodsWe 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 30 days after infection-related hospitalization. We also studied death due to infection within 30 days after admission.ResultsWe 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 30 days 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.ConclusionsPre-existing unipolar depression is associated with slightly increased mortality following hospitalization for an infection.