HMPV is a paramyxovirus discovered in 2001 that causes seasonal respiratory infections (bronchiolitis, pneumonia) similar in severity to RSV, especially in young children and the elderly. It is clinically relevant to include because HMPV accounts for a significant fraction of pediatric hospitalizations (on the order of 5–10% annually) and can cause outbreaks of severe lower respiratory disease Charlton et al. 2018, Panda et al. 2014).
Charlton, C. L., Babady, E., Ginocchio, C. C., Hatchette, T. F., Jerris, R. C., Li, Y., Loeffelholz, M., McCarter, Y. S., Miller, M. B., Novak-Weekley, S., Schuetz, A. N., Tang, Y. W., Widen, R., & Drews, S. J. (2018). Practical Guidance for Clinical Microbiology Laboratories: Viruses Causing Acute Respiratory Tract Infections. Clinical microbiology reviews, 32(1), e00042-18. https://doi.org/10.1128/CMR.00042-18
Panda, S., Mohakud, N. K., Pena, L., & Kumar, S. (2014). Human metapneumovirus: review of an important respiratory pathogen. International journal of infectious diseases : IJID : official publication of the International Society for Infectious Diseases, 25, 45–52. https://doi.org/10.1016/j.ijid.2014.03.1394