Characteristics and Risk Factors Associated With Hospitalization and Severe Disease in Patients Aged ≥ 60 Years With Human Metapneumovirus Infection Over Three Consecutive Seasons (2021–2024) in Valladolid, Spain. The VALLAVIRUS Study

BACKGROUND: Human metapneumovirus (hMPV) is a respiratory pathogen often underestimated in the elderly. Although studies suggest it causes around 10% of respiratory hospitalizations in the United States, national and local data remain scarce. This study aimed to describe patients hospitalized with hMPV and identify risk factors for hospitalization and severe disease. METHODS: A retrospective study included adults aged ≥ 60 years diagnosed with hMPV infection in two hospitals in Valladolid, Spain, during three consecutive seasons (2021-2024). Data on demographics, comorbidities, clinical presentation, laboratory results and severity parameters were collected. Severe disease was defined as hospital stay ≥ 11 days, ICU admission, need for mechanical ventilation, readmission within 90 days or in-hospital death. RESULTS: Among 703 hMPV-confirmed cases, 608 required hospitalization, following a clear seasonal epidemic pattern (November-March). The hospitalization rate was 123.2 per 100,000 > 60 years old inhabitants (95% CI: 113.6-133.4), representing 20.5% of respiratory virus detections. Mean hospital stay was 10.5 days; 6.4% of the patients were admitted to ICU, 3.3% required mechanical ventilation, 6.9% died, and 14.0% were readmitted within 90 days. Advanced age (≥ 75 years) increased hospitalization risk threefold to fivefold compared to people between 60 and 74 years old. Co-infections, particularly bacterial, and living in nursing homes were also associated with a 1.5-2.7 fold higher risk of severe disease and hospitalization. CONCLUSIONS: hMPV infections pose a significant health burden among the elderly. The findings underscore the need for greater awareness, surveillance, and development of preventive strategies, including vaccination, against hMPV in older adults.