Respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) are increasingly being recognized as important viral pathogens in adults, particularly in advanced age and high-risk populations. However, epidemiological and clinical data on RSV and hMPV pneumonia in Japan are limited. We conducted a retrospective cohort study of adult patients diagnosed with RSV, hMPV, or influenza virus pneumonia at eight institutions in Nagasaki. Clinical information, including the Charlson Comorbidity Index (CCI), laboratory and radiological findings, were collected from medical records. Pneumonia severity was assessed using the A-DROP and Pneumonia Severity Index (PSI). A total of 301 patients were included: 215 with influenza, 34 with RSV, and 52 with hMPV pneumonia. The median ages were 75, 82, and 69 years, respectively. Female predominance was observed in RSV and hMPV cases compared with influenza. RSV cases were more frequently associated with residence in long-term care facilities, lower BMI, and higher prevalence of chronic cardiopulmonary disease. Lower respiratory tract symptoms, particularly cough and sputum production, were significantly more frequent in patients with RSV infections. hMPV cases exhibited lower CCI scores and milder severity profiles. The A-DROP and PSI scores did not differ significantly between RSV and influenza, and the in-hospital mortality was comparable across the groups. RSV and hMPV are clinically important causes of pneumonia in advanced aged Japanese population. RSV pneumonia is associated with prominent respiratory symptoms and radiological findings, with severity comparable to that of influenza. These findings underscore the need for increased awareness and large-scale, prospective studies.
Takao et al. (Wed,) studied this question.