Kwayar cutar syncytial ta numfashi kwayar cutar RNA ce wadda ta samo asali daga dangin Pneumovirus, wato dangin Pneumovirinae. Ana yaɗa ta ne ta hanyar digo, kuma hulɗa kai tsaye da yatsan da kwayar cutar syncytial ta gurbata da yatsar da ta shafa da mucosa na hanci da mucosa na ido shi ma muhimmin hanyar yaɗawa ne. Kwayar cutar syncytial ta numfashi ita ce sanadin ciwon huhu. Bayan lokacin da aka kamu da cutar, kwayar cutar syncytial ta numfashi za ta haifar da zazzabi, zubar hanci, tari da kuma wani lokacin hura hanci. Kwayar cutar syncytial ta numfashi na iya faruwa a tsakanin al'ummomin kowace shekara, inda tsofaffi da mutanen da ke da matsalar huhu, zuciya ko garkuwar jiki suka fi kamuwa da cutar.