The Impact of Thrombocytopenia and Lymphopenia on Mortality in Patients Infected with Influenza Virus: A Retrospective Cohort Study

Abstract

<b><i>Introduction:</i></b> 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. <b><i>Methods:</i></b> This single-center, retrospective, cohort study included consecutive adult patients, hospitalized in Rabin Medical Center between October 2017 and April 2018, with laboratory-confirmed influenza. Patients were grouped according to blood counts on admission: (1) thrombocytopenia (&lt;150 K/mL), (2) lymphopenia (&lt;0.5 K/mL), and (3) both thrombocytopenia and lymphopenia. Patients without thrombocytopenia and lymphopenia were designated as controls. The primary outcome was 30-day all-cause mortality. Risk factors were identified by univariable and multivariable analyses, using logistic regression and reported as odds ratios (ORs) and 95% confidence intervals (CIs). <b><i>Results:</i></b> A total of 625 patients were included, 112 (18%) had thrombocytopenia, 98 (15.6%) had lymphopenia, and 107 (17%) had both. The crude 30-day 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 versus 4.2% (13/308) in the control (<i>p</i> = 0.000 for all). In a multivariable regression model, significant thrombocytopenia (&lt;100 K/μL) [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% CI 1.002–1.11)], and significant respiratory support [OR 8.85 (3.4–22.6)] were associated with 30-day all-cause mortality. <b><i>Conclusion:</i></b> Patients hospitalized with seasonal influenza and thrombocytopenia &lt;100 K/mL on admission, have an increased 30-day all-cause mortality.