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Influenza Other Respir Viruses
. 2026 Mar;20(3):e70238.
doi: 10.1111/irv.70238.
Incidence of RSV- and Influenza-Associated Hospitalizations With Community-Acquired Pneumonia and Other Acute Respiratory Infection Among Adults in Japan in 2022-2024: APSG-J2 Study
Haruka Maeda 1 , Shingo Masuda 1 2 , Bhim Gopal Dhoubhadel 1 , Yuka Fujita 3 , Yuji Akiba 4 , Yutaka Nishigaki 4 , Kei Nakashima 5 , Hiroyuki Ito 1 5 , Masayuki Nogi 6 , Yoshihito Otsuka 7 , Masayuki Ishida 8 , Eiji Takeuchi 9 , Norichika Asoh 10 , Toyomitsu Sawai 11 , Koichi Hayakawa 12 , Eileen M Dunne 13 , Claudia Schwarz 13 , Bradford D Gessner 13 , Elizabeth Begier 13 , Shuhei Ito 14 , Ataru Igarashi 15 , Shinobu Osanai 16 , Konosuke Morimoto 1 , Koya Ariyoshi 2 ; Adult Pneumonia Study Group‐Japan 2 (APSG‐J2)
Affiliations
Background: Quantifying the burden of respiratory syncytial virus (RSV) in adults is challenging compared to influenza, and data among older adults remain scarce in Japan. Country-specific evidence is essential to support RSV vaccination policy.
Methods: This prospective, multicenter study (APSG-J2) targeted hospitalized adults with community-acquired pneumonia (CAP) and other acute respiratory infections (ARI) in seven community hospitals across four catchment areas in Japan between September 2022 and August 2024. Respiratory samples were analyzed using a multiplex polymerase chain reaction (PCR) kit to detect RSV and influenza. Incidence rates of RSV- and influenza-associated hospitalizations were estimated using study data and national statistics, stratified by age and region.
Results: Among 3047 hospitalized patients with CAP/ARI, 1499 (49.2%) underwent multiplex PCR testing. RSV and influenza were detected in 2.8% and 3.3% of tested patients, respectively. The incidences of RSV-associated CAP/ARI hospitalizations among adults aged ≥ 65 years were 29 and 36 per 100,000 person-years in the first and second years, respectively, with higher incidences among those aged ≥ 85 years (150 and 131 per 100,000 person-years). Influenza incidence increased markedly in the second year (from 11 to 71 per 100,000 person-years for adults age ≥ 65 years), possibly reflecting post-COVID-19 transmission changes.
Conclusions: In this multicenter study, we estimated the incidence of RSV- and influenza-associated hospitalizations among adults in Japan. The findings indicated that the incidence increased with age, and influenza-associated hospitalizations increased in the second year. Continued surveillance is essential to accurately assess RSV burden in the adult population.
Keywords: Japan; adult; community‐acquired pneumonia; influenza; respiratory syncytial virus.
. 2026 Mar;20(3):e70238.
doi: 10.1111/irv.70238.
Incidence of RSV- and Influenza-Associated Hospitalizations With Community-Acquired Pneumonia and Other Acute Respiratory Infection Among Adults in Japan in 2022-2024: APSG-J2 Study
Haruka Maeda 1 , Shingo Masuda 1 2 , Bhim Gopal Dhoubhadel 1 , Yuka Fujita 3 , Yuji Akiba 4 , Yutaka Nishigaki 4 , Kei Nakashima 5 , Hiroyuki Ito 1 5 , Masayuki Nogi 6 , Yoshihito Otsuka 7 , Masayuki Ishida 8 , Eiji Takeuchi 9 , Norichika Asoh 10 , Toyomitsu Sawai 11 , Koichi Hayakawa 12 , Eileen M Dunne 13 , Claudia Schwarz 13 , Bradford D Gessner 13 , Elizabeth Begier 13 , Shuhei Ito 14 , Ataru Igarashi 15 , Shinobu Osanai 16 , Konosuke Morimoto 1 , Koya Ariyoshi 2 ; Adult Pneumonia Study Group‐Japan 2 (APSG‐J2)
Affiliations
- PMID: 41833535
- DOI: 10.1111/irv.70238
Background: Quantifying the burden of respiratory syncytial virus (RSV) in adults is challenging compared to influenza, and data among older adults remain scarce in Japan. Country-specific evidence is essential to support RSV vaccination policy.
Methods: This prospective, multicenter study (APSG-J2) targeted hospitalized adults with community-acquired pneumonia (CAP) and other acute respiratory infections (ARI) in seven community hospitals across four catchment areas in Japan between September 2022 and August 2024. Respiratory samples were analyzed using a multiplex polymerase chain reaction (PCR) kit to detect RSV and influenza. Incidence rates of RSV- and influenza-associated hospitalizations were estimated using study data and national statistics, stratified by age and region.
Results: Among 3047 hospitalized patients with CAP/ARI, 1499 (49.2%) underwent multiplex PCR testing. RSV and influenza were detected in 2.8% and 3.3% of tested patients, respectively. The incidences of RSV-associated CAP/ARI hospitalizations among adults aged ≥ 65 years were 29 and 36 per 100,000 person-years in the first and second years, respectively, with higher incidences among those aged ≥ 85 years (150 and 131 per 100,000 person-years). Influenza incidence increased markedly in the second year (from 11 to 71 per 100,000 person-years for adults age ≥ 65 years), possibly reflecting post-COVID-19 transmission changes.
Conclusions: In this multicenter study, we estimated the incidence of RSV- and influenza-associated hospitalizations among adults in Japan. The findings indicated that the incidence increased with age, and influenza-associated hospitalizations increased in the second year. Continued surveillance is essential to accurately assess RSV burden in the adult population.
Keywords: Japan; adult; community‐acquired pneumonia; influenza; respiratory syncytial virus.