ʻO ka maʻi syncytial hanu kahi maʻi RNA nona ka genus Pneumovirus, ʻohana Pneumovirinae. Hoʻolaha nui ʻia ia ma o ka hoʻoili ʻana o ka kulu, a ʻo ka pili pololei ʻana o ka manamana lima i haumia ʻia e ka maʻi syncytial hanu me ka mucosa ihu a me ka mucous o ka maka he ala nui nō hoʻi ia o ka hoʻoili ʻana. ʻO ka maʻi syncytial hanu ke kumu o ka pneumonia. I ka wā hoʻoulu ʻia, e hoʻoulu ka maʻi syncytial hanu i ke kuni, ka ihu holo, ka ʻūhā a i kekahi manawa ka hanu ʻana. Hiki ke loaʻa ka maʻi maʻi syncytial hanu i waena o nā heluna kanaka o kēlā me kēia hui makahiki, kahi e ʻoi aku ka maʻi o nā poʻe ʻelemakule a me nā poʻe me nā māmā, ka puʻuwai a i ʻole ka ʻōnaehana pale.