Human Metapneumovirus-Associated Hospitalization Burden in Children Aged Under 5 Years in Scotland Between 2017 and 2023: a Retrospective Analysis.

Background: Human metapneumovirus (hMPV) is commonly associated with respiratory tract infections (RTIs) in young children. Method: We estimated the annual hospital incidence of hMPV RTIs in children under 5 years in Scotland from 2017 to 2023 using national hospital and laboratory data. Incidence outside Lothian, where testing practices were uncertain, was extrapolated from Lothian laboratory data, where hMPV testing was advised for all RTI admissions. We also examined the severity and mortality of laboratory-confirmed hMPV cases. We developed similar estimates for respiratory syncytial virus (RSV) and influenza A for comparison. Results: This analysis included 1462 laboratory-confirmed hMPV hospitalizations in children aged under 5 years. The extrapolated hMPV hospital incidence ranged from 19 per 100 000 to 537 per 100 000 in children aged under 5 years. The extrapolated incidence was 2 to 3 times higher than that based on laboratory-confirmed data. Hospital incidence was higher in infants than in toddlers. hMPV incidence dropped substantially during the 2020/21 season, followed by a rebound during the 2021/22 season. About 10% of hMPV RTI hospital admissions required hospital stay ≥5 days, but <1% required intensive care unit admissions or resulted in in-hospital death. RSV hospital incidence appeared substantially higher than the hMPV hospital incidence in this population. Conclusions: hMPV RTIs contribute to a substantial hospital burden in young children in Scotland. However, the RSV RTI burden is likely to be higher in the population unvaccinated against both viruses. Improved surveillance and diagnosis strategies are required to develop robust hospital burden estimates.