Severity of influenza virus and respiratory syncytial virus coinfections in hospitalized adult patients

Background: With the introduction of molecular diagnostic techniques over the past decades, different kinds of viral pathogens in the same sample are detected simultaneously more frequently. Nevertheless, influenza virus (Flu) and respiratory syncytial virus (RSV) coinfection in adults was reported only occasionally. Moreover, the clinical implications of Flu/RSV coinfection in the respiratory tract of adults remain unclear. Methods: This retrospective study analyzed adult patients with acute respiratory infection from January 2017 to June 2019 in China-Japan Friendship Hospital. Results: A total of 574, 235 and 113 patients were positive for influenza A-only (FA-only), influenza B-only (FB-only) and RSV-only in influenza seasons (from Nov 2017 to Mar 2018 and from Nov 2018 to Mar 2019), respectively. Of these, 19 cases were coinfected by Flu and RSV and admitted to this hospital. Compared with 809 Flu-only infected patients and 113 RSV-only infected patients, both the rates of intensive care unit(ICU) admission and use of invasive mechanical ventilation in Flu/RSV coinfected patients were higher (ICU admission: 47.4% vs. 20.1%, P=0.004; 47.4% vs. 22.1%, P=0.020; invasive mechanical ventilation: 47.4% vs.13.2%, P<0.001; 47.4% vs. 17.7%, P=0.004). Furthermore, 60-day all-cause mortality attributed to Flu/RSV coinfections was significantly greater than that for Flu and RSV mono-infected patients (36.8% vs. 8.0%,P<0.001; 36.8% vs. 11.5%, P=0.004. Conclusion: The findings of this study suggest that coinfection of Flu/RSV in adults is associated with a high adverse outcome. Thus, Flu/RSV coinfections should be increasingly appreciated and given appropriate management.