Causes

Diphtheria is caused by the bacterium Corynebacterium diphtheriae. The bacterium usually multiplies on or near the surface of the throat or skin. C. diphtheriae spreads through:

• Airborne droplets. When an infected person's sneeze or cough releases a mist of contaminated droplets, people nearby may inhale C. diphtheriae. Diphtheria spreads easily this way, especially in crowded conditions.

• Contaminated personal or household items. People sometimes catch diphtheria from handling an infected person's things, such as used tissues or hand towels, that may be contaminated with the bacteria.

  You can also transfer diphtheria-causing bacteria by touching an infected wound.

People who have been infected by the diphtheria bacteria and who haven't been treated can infect people who haven't had the diphtheria vaccine — even if they don't show any symptoms.