Maintenance Immunosuppression Is Associated With Better Outcome in the 2017/2018 Influenza Epidemic

BACKGROUND: The impact of immunosuppression on outcomes in influenza is insufficiently understood. We analyzed the morbidity and mortality of immunocompetent (IC) vs immunosuppressed (IS) patients with influenza A and B in the 2017/2018 season. METHODS: Patients with proven influenza in a German tertiary care hospital were analyzed for hospitalization, intensive care unit (ICU) admission, and mortality. Causes for IS were organ and bone marrow transplantation, AIDS, chemotherapy, and medical immunosuppression. RESULTS: In total, 227 patients were included in this analysis (IC, n = 118 [52%]; IS, n = 109 [48%]). Hospitalization (71% vs 91%; P < .001) and ICU admission (7% vs 23%; P = .001) were less frequent in the IS compared with the IC group. IC patients had a higher need for invasive ventilation (20% vs 5%; P = .001), vasopressors (19% vs 4%; P < .001), and renal replacement therapy (15% vs 3%; P = .002). Influenza-associated cardiomyopathy was found in 18% of IC vs 2% of IS patients (P < .001). The 30-day in-hospital mortality was 6.6%, 10.2% in the IC group and 2.8% in the IS group (hazard ratio IS group, 0.259; 95% confidence interval [CI], 0.113–0.855; P = .023). Immunosuppression was associated with reduced mortality (odds ratio, 0.25; 95% CI, 0.07–0.91; P = .036). CONCLUSIONS: We observed that IS was not associated with a worse outcome in this influenza cohort. Due to the presence of both confounding and referral and selection bias, the conclusion that immunosuppression reduces mortality cannot be drawn. Prospective studies investigating the influence of baseline immunosuppression on severity of influenza infection are desirable.