Effect of Influenza on Outcomes in Patients With Heart Failure

Objectives: This study sought to determine whether influenza infection increases morbidity and mortality in patients hospitalized with heart failure (HF). Background: Patients with HF may be at increased risk of morbidity and mortality from influenza infection. However, there are limited data for the associated hazards of influenza infection in patients with HF. Methods: We queried the 2013 to 2014 National Inpatient Sample database for all adult patients (18 years of age or older) admitted with HF with and without concomitant influenza infection. Propensity score matching was used to match patients across age, race, sex, and comorbidities. Outcomes included in-hospital mortality, in-hospital complications, length of stay, and average hospital costs. Results: Of 8,189,119 all-cause hospitalizations in patients with HF, 54,590 (0.67%) had concomitant influenza infection. Patients with concomitant influenza had higher incidence of in-hospital mortality (6.2% vs. 5.4%, respectively; odds ratio [OR]: 1.15 [95% confidence interval [CI]: 1.03 to 1.30]; p = 0.02), acute respiratory failure (36.9% vs. 23.1%, respectively; OR: 1.95 [95% CI: 1.83 to 2.07]; p < 0.001), acute respiratory failure requiring mechanical ventilation (18.2% vs. 11.3%, respectively; OR: 1.75 [95% CI: 1.62 to 1.89]; p < 0.001), acute kidney injury (AKI) (30.3% vs. 28.7%, respectively; OR: 1.08 [95% CI: 1.02 to 1.15]; p = 0.01), and AKI requiring dialysis (2.4% vs. 1.8%, respectively; OR: 1.37 [95% CI: 1.14 to 1.65]; p = 0.001). Patients with influenza had longer mean lengths of stay (5.9 days vs. 5.2 days, respectively; p <0.001) but similar average hospital costs ($12,137 vs. $12,003, respectively; p = 0.40). Conclusions: Influenza infection is associated with increased in-hospital morbidity and mortality in patients with HF. Our results emphasize the need for efforts to mitigate the incidence of influenza, specifically in this high-risk patient cohort.