Ten-Year Surveillance of RSV Hospitalizations in Adults: Incidence Rates and Case Definition Implications.

Abstract

Introduction: The impact of RSV in older adults is under-recognized, and the limited existing studies on the incidence of hospitalizations show great variability. This study aims to estimate the seasonal incidence rates (IRs) of RSV hospitalizations among adults aged 60 and older (≥60) and evaluate how different case definitions influence these estimates.

Methods: A prospective, multicentre observational study with active monitoring conducted over 10 seasons (2010/2011 to 2019/2020) in 4-10 hospitals (depending on the season) that covered 21-46% of the region's total population (around 5 million people). RSV-hospitalization IRs per 100,000 person-years (p-y) and 95% confidence intervals (CI) were calculated by the Exact Poisson method, and were stratified by age group (≥60, ≥70, and ≥80), RSV season, sex, and the entire study period. Two case definitions were compared: influenza-like illness (ILI) and the combined use of ILI and extended severe acute respiratory infection (ILI/SARI).

Results: A total of 40,600 hospitalizations of individuals aged ≥60 were included. The RSV-hospitalization IRs ranged from 21 to 402 per 100,000 p-y, varying by season, age group and case definition. The highest IRs were observed in those aged 80 and older. The ILI case definition underestimated RSV hospitalizations by 13% to 40% when compared to the ILI/SARI case definition.

Conclusion: On average, approximately 1 every 1,000 adults ≥60 is hospitalized due to RSV. The risk of a severe RSV infection increases with age and varies significantly between seasons. These are key results for the estimation of the potential impact of the new available RSV vaccines.