It is an acute, highly contagious infection, caused by the bacteria coryne bacterium diphtheria, generally affecting the throat but occasionally other mucus membranes and the skin. The disease is spread by direct contact with a patient or a carrier or by contaminated food. After an incubation period sore throat, weakness, and mild fever develop. Later a soft grey membrane forms across the throat, constricting the air passage and causing difficulty in breathing and swallowing. A tracheostomy may be necessary. Bacteria multiply in that infected area and release a toxin into the blood stream, which damage heart and nerves. Death from heart failure or general collapse can follow within four days but disease, complete recovery required prolonged bed rest. An effective immunization programmer has now made diphtheria rare.