CDC describes diphtheria as "an upper respiratory tract illness characterized by sore throat, low-grade fever, and an adherent membrane of the tonsil(s), pharynx, and/or nose". Diphtheria is a rapidly developing, acute, febrile infection which involves both local and systemic pathology. A local lesion develops in the upper respiratory tract and involves necrotic injury to epithelial cells. As a result of this injury, blood plasma leaks into the area and a fibrin network forms which is interlaced with with rapidly-growing C. diphtheriae cells.