Human Metapneumovirus-associated Hospital Burden in Older Adults in Scotland: A Retrospective Analysis.

Background: Human metapneumovirus (hMPV) is commonly associated with respiratory tract infections (RTIs) in older adults. Method: We estimated the annual hospital incidence of hMPV RTIs in older adults in Scotland over 6 seasons (2017-2023) using national hospital and laboratory data. Hospital incidence in Scottish health boards other than Lothian, where testing practices were uncertain, was extrapolated using Lothian's comprehensive laboratory data. We also assessed the severity and mortality outcomes of laboratory-confirmed hMPV episodes in older adults in Scotland. Additionally, we developed similar estimates for respiratory syncytial virus (RSV) and Influenza A for comparisons. Results: This analysis included 626 laboratory-confirmed hMPV hospitalizations. Only 28% of laboratory-confirmed hMPV episodes were clinically coded. The extrapolated hMPV hospital incidence ranged from 3.6/100 000 to 49.5/100 000 in adults aged ≥60 y in Scotland, and the extrapolated incidence was 1.3 to 3.8 times higher than the incidence of laboratory-confirmed data. The hospital incidence was higher in ≥75 y than in 60-74 y. hMPV incidence dropped substantially during the COVID-19 pandemic. The case fatality rates were higher in the ≥75 y compared with the 60-74 y, but ICU admissions were more common in the 60-74 y. The hospital incidence of RSV and Influenza A seemed higher than hMPV, but the 95% confidence intervals for severity and outcomes generally overlapped. Conclusions: hMPV RTIs pose a substantial hospital burden in older adults in Scotland. The differences between laboratory-confirmed and extrapolated estimates highlight the need for improved surveillance, diagnosis, and coding practices to develop robust burden estimates. The clinical severity of hMPV could be similar to RSV.