Abstract
INTRODUCTION: Older adults (OAs) and individuals with underlying comorbidities are at increased risk for severe respiratory syncytial virus (RSV) disease (e.g., lower respiratory tract disease [LRTD]) and related adverse outcomes. However, RSV is underdiagnosed and underestimated in OAs, posing a growing concern in super-aged societies like Japan. METHODS: This prospective, multicenter, epidemiological study (Nagasaki ROAD) aimed to enroll approximately 2700 participants aged ≥ 50 years with acute respiratory infection (ARI) seeking care at outpatient/emergency/inpatient settings at 15 medical institutions/hospitals/clinics in Nagasaki and its surroundings. Enrolled participants were followed for 180 days. RSV positivity in nasopharyngeal swab samples, detected by reverse transcription polymerase chain reaction, served as the primary diagnosis of RSV-related ARI/LRTD (RSV-ARI/LRTD). Hospital-wide and non-hospital-wide screening were adopted based on site-level operational realities and clinical workflows. RESULTS: Data at enrollment (baseline/day 1) were analyzed from 1056 participants who were recruited between April 1, 2024 and March 31, 2025. The approximate positivity rate of RSV-ARI was 5.0% (n = 53), peaking from June to September 2024. The approximate positivity rate of SARS-CoV-2-ARI was 25.4% (n = 268), and influenza-ARI was 19.6% (n = 207). Hospitalization at or within 7 days of day 1 was observed in 20.8% (n = 11) of participants with RSV-ARI, 13.1% (n = 35) with SARS-CoV-2-ARI, and 13.0% (n = 27) with influenza-ARI. The most common comorbidities-of-interest were asthma (17.0% [n = 9]), chronic obstructive pulmonary disease (15.1% [n = 8]), and type 2 diabetes mellitus (7.5% [n = 4]) in participants with RSV-ARI. The observed need for oxygen supplementation was higher in participants with RSV-ARI (13.2% [n = 7]) than with SARS-CoV-2-ARI (3.4% [n = 9]) or influenza-ARI (8.7% [n = 18]). CONCLUSIONS: These year 1 results contextualize the RSV disease burden in OAs aged ≥ 50 years in Nagasaki, Japan, providing an important basis for understanding RSV in Japanese OAs; findings complement existing evidence. Future analyses of all clinical outcomes through 180-day follow-up could further inform targeted prevention strategies in this population.