Diphtheria is a disease caused by a bacterium, Corynebacterium diphtheriae
, that usually affects the tonsils, throat, nose and/or skin. It is passed from person to person by droplet transmission, usually by breathing in diphtheria bacteria after an infected person has coughed or sneezed. Although diphtheria disease is rare in the U.S., it appears that C diphtheriae continues to circulate in areas of the country with previously endemic diphtheria. Diphtheria also occurs in many other parts of the world.