Diphtheria is a contagious bacterial disease that produces thick, gray membranes in the mouth, throat, and airway passages. The disease occurs largely because of a toxin produced by the infecting bacteria, Corynebacterium diphtheriae. Diptheria can lead to difficulty in breathing, pneumonia, heart failure, even paralysis and death. The entire process was described in epidemics in Europe in the 1500s and 1600s and in New England in the 1800s. In the United States, all 50 states have laws requiring immunization against diphtheria before entering school. The use of the DTP and DTaP vaccine has made the disease almost nonexistent in the United States.