Supplementary Material for: The impact of thrombocytopenia and lymphopenia on mortality in patients infected with Influenza virus – a retrospective cohort study

Introduction Influenza virus causes significant global annual morbidity and mortality. Thrombocytopenia is recognized as a poor prognostic factor in sepsis and is associated with mortality, while lymphopenia has been established as a poor prognostic factor in other viral infections. We aimed to assess the incidence of thrombocytopenia and lymphopenia in seasonal influenza and their effect on clinical outcomes. Methods This single-center, retrospective, cohort study included consecutive adult patients, hospitalized in Rabin Medical Center between October 2017 - April 2018, with laboratory confirmed influenza. Patients were grouped according to blood counts on admission: 1. Thrombocytopenia (<150 K/ml), 2. lymphopenia (<0.5K/ml), and 3. both thrombocytopenia and lymphopenia. Patients without thrombocytopenia and lymphopenia were designated as controls. The primary outcome was 30-days all-cause mortality. Risk factors were identified by univariable and multivariable analyses, using logistic regression and reported as odds ratios (OR) and 95% confidence intervals (CI). Results A total of 625 patients were included, 112 (18%) had thrombocytopenia, 98 (15.6%) had lymphopenia and 107 (17%) had both. The crude 30-days all-cause mortality was 7.6% (48/625). Mortality rates were 7.1% (8/112) for the thrombocytopenia group, 11.2% (11/98) for the lymphopenia group, and 14.9% (16/107) for patients with both vs 4.2% (13/308) in the control (p=0.000 for all). In a multivariable regression model, significant thrombocytopenia (<100 K/microL) [OR 5.07, (95% CI 1.5-16.2)[, age [OR 1.07, (95% CI 1.02-1.11)], time to oseltamivir ]OR 1.006, (95%1.002-1.11)], and significant respiratory support [OR 8.85, (3.4-22.6)], were associated with 30-day all-cause mortality. Conclusion Patients hospitalized with seasonal influenza and thrombocytopenia < 100K/mL on admission, have an increased 30-days all-cause mortality.