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Randomized Controlled Trial
. 2025 Mar;18(3):102653.
doi: 10.1016/j.jiph.2025.102653. Epub 2025 Jan 3.

Exploring case definitions and the natural history of respiratory syncytial virus in adult outpatients: First-season results of the RESPIRA-50 study

Alexander Domnich  1 , Francesco Lapi  2 , Andrea Orsi  3 , Piero Luigi Lai  4 , Luca Pestarino  5 , Pier Claudio Brasesco  6 , Marta Vicentini  7 , Anna Puggina  7 , Alen Marijam  8 , Carlo-Simone Trombetta  9 , Giada Garzillo  9 , Giulia Guarona  9 , Federica Stefanelli  10 , Valentina Ricucci  10 , Donatella Panatto  4 , Giancarlo Icardi  3
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Free article
Randomized Controlled Trial

Exploring case definitions and the natural history of respiratory syncytial virus in adult outpatients: First-season results of the RESPIRA-50 study

Alexander Domnich et al. J Infect Public Health. 2025 Mar.
Free article

Abstract

Background: Data on the natural history of the community-acquired RSV in adult outpatients are limited. It is also unclear whether the existing influenza surveillance platforms based on influenza-like illness (ILI) case definitions are efficient for RSV. The two-season RESPIRA-50 study was established in 2023 to identify an optimal RSV case definition and to explore the natural history of RSV. Here, the first-season results are reported.

Methods: The study was conducted in Genoa (Italy) during the 2023/2024 RSV season. Twenty-four general practitioners were randomized 1:1 to enroll adults aged ≥ 50 years seeking care for acute respiratory infection (ARI) or ILI, respectively. Both syndromes were defined according to the European criteria. All subjects were tested by real-time polymerase chain reaction (RT-PCR) for RSV and other pathogens. RSV-positive adults were followed for up to 30 days.

Results: Of 517 subjects included, 7.0 % [95 % confidence interval (CI): 4.9-9.5 %)] tested positive for RSV. RSV prevalence in the ARI group (8.0 %; 95 % CI: 5.0-12.1 %) was higher than in the ILI group (6.0 %; 95 % CI: 3.5-9.5 %) with an odds ratio of 1.36 (95 % CI: 0.69-2.70). Conversely, positivity for influenza (10.4 % vs 12.4 %) and SARS-CoV-2 (12.4 % vs 16.9 %) were lower in the ARI group and the corresponding ORs were 0.82 (95 % CI: 0.48-1.42) and 0.70 (95 % CI: 0.43-1.15), respectively. The mean duration of an RSV episode was 18.8 ± 8.0 days and two thirds of individuals were prescribed antibiotics. A total of 33.3 % (95 % CI: 18.6-51.0 %) of RSV-positive individuals developed complications, of which bronchitis (13.9 %) and pneumonia (8.3 %) were the most frequent.

Conclusions: Compared with ARI, ILI-based surveillance may underestimate the burden of RSV in community-dwelling adults aged ≥ 50 years. A high proportion of RSV-positive adult outpatients develops complications, which lead to substantial resource consumption.

Keywords: Acute respiratory infection; Burden of disease; Case definition; RSV; Respiratory syncytial virus; Surveillance.

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Conflict of interest statement

Declaration of Competing Interest A.D. provided consultancies and received speaker fees from CSL Seqirus, GSK and SD Biosensor. A.O. provided consultancies and/or received speaker fees from CSL Seqirus, Moderna, Novavax and SD Biosensor. M.V., A.P. and A.M. are employees of the GSK group of companies and may hold shares in the GSK group of companies as part of their employee remuneration. D.P. provided consultancies for Pfizer and CSL Seqirus and received grants for conducting observational studies from Sanofi, Pfizer, GSK and Viatris. G.I. provided consultancies and/or received grants for conducting experimental and/or observational studies for GSK, Sanofi, MSD, CSL Seqirus and Pfizer. Other authors declare no conflicts of interest.

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