Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Diphtheria is an upper respiratory tract illness caused by Corynebacterium diphtheriae, a facultative anaerobic, Gram-positive bacterium. It is characterized by sore throat, low fever, and an adherent membrane on the tonsils, pharynx, and/or nasal cavity. Diphtheria is a contagious disease spread by direct physical contact or breathing the aerosolized secretions of infected individuals. Learn more about diphtheria, its causes, symptoms and treatment in the following pages.