Clinical characteristics and population-based attack rates of respiratory syncytial virus versus influenza hospitalizations among adults-An observational study

Background The clinical significance of respiratory syncytial virus (RSV) among adults remains underinvestigated. We compared the characteristics and population-based attack rates of RSV and influenza hospitalizations. Methods During 2018-2020, we recruited hospitalized adults with respiratory infection to our prospective substudy at a tertiary care hospital in Finland and compared the characteristics of RSV and influenza patients. In our retrospective substudy, we calculated the attack rates of all RSV and influenza hospitalizations among adults in the same geographic area during 2016-2020. Results Of the 537 prospective substudy patients, 31 (6%) had RSV, and 106 (20%) had influenza. Duration of hospitalization, need for intensive care or outcome did not differ significantly between RSV and influenza patients. RSV was more often missed or its diagnosis omitted from medical record (13% vs. 1%, p = 0.016 and 52% vs. 85%, p < 0.001). In the retrospective substudy, the mean attack rates of RSV, influenza A, and influenza B hospitalizations rose with age from 4.1 (range by season 1.9-5.9), 15.4 (12.3-23.3), and 4.7 (0.5-16.2) per 100,000 persons among 18- to 64-year-olds to 58.3 (19.3-117.6), 204.1 (31.0-345.0), and 60.4 (0.0-231.0) per 100,000 persons among 65+-year-olds and varied considerably between seasons. Discussion While the attack rates of influenza hospitalizations were higher compared with RSV, RSV and influenza hospitalizations were similar in severity. Missing or underreporting of RSV infections may lead to underestimating its disease burden. Both RSV and influenza caused a substantial amount of hospitalizations among the elderly, stressing the need for more effective interventions.