Depression is associated with decreased severity and lower mortality in non-elderly hospitalized adults with influenza in the United States

Background: Depression is associated with risk for chronic disease, though its relationship with infectious diseases is less understood. Depression may modify the clinical outcomes of patients with infectious diseases such as influenza via its association with inflammation. The objective of this study was to evaluate the relationships between depression and clinical outcomes in non-elderly adults with influenza infection. Methods: This was a secondary analysis of the Nationwide Inpatient Sample database, years 2012-2016. Hospitalized adults aged 18-65 admitted during each influenza season were included. Depression status was documented via ICD-10 codes. The association between depression and clinical outcomes (e.g. disease severity, length of hospital stay, and inpatient all-cause mortality) were evaluated using multivariable regression modeling. Results: A total of 44,292 patients were included, 12% with depression. After adjustment for confounding, non-elderly influenza patients with depression had a 3.8% decreased risk of a severe disease (95% CI: 1.9% - 5.7%; P<0.001), no difference in length of stay (Hazard Ratio: 0.99, 95% Confidence Interval 0.96 – 1.02), and lower all-cause in-hospital mortality versus those without depression (Odds Ratio=0.76; 95% CI 0.59 - 0.97; P=0.028). Conclusions: This study suggests that in non-elderly hospitalized patients with influenza, depression is associated with a decreased severity of illness and acute mortality. Chronic inflammation in those with depression may enhance the ability of the immune response to limit influenza infection or reduce pathologic acute inflammation associated with influenza disease.