Diphtheria is an infection caused by the bacterium Corynebacterium diphtheriae. Most infections are asymptomatic or have a mild clinical course, but in some outbreaks more than 10% of those diagnosed with the disease may die. Signs and symptoms may vary from mild to severe and usually start two to five days after exposure. Symptoms often come on fairly gradually, beginning with a sore throat and fever. In severe cases, a grey or white patch develops in the throat. This can block the airway and create a barking cough as in croup. The neck may swell in part due to enlarged lymph nodes. A form of diphtheria which involves the skin, eyes or genitals also exists. Complications may include myocarditis, inflammation of nerves, kidney problems, and bleeding problems due to low levels of platelets. Myocarditis may result in an abnormal heart rate and inflammation of the nerves may result in paralysis. Diphtheria is usually spread between people by direct contact or through the air. It may also be spread by contaminated objects. Some people carry the bacterium without having symptoms, but can still spread the disease to others. The three main types of C. diphtheriae cause different severities of disease. The symptoms are due to a toxin produced by the bacterium. Diagnosis can often be made based on the appearance of the throat with confirmation by microbiological culture. Previous infection may not protect against infection. A diphtheria vaccine is effective for prevention and available in a number of formulations. Three or four doses, given along with tetanus vaccine and pertussis vaccine, are recommended during childhood. Further doses of diphtheria–tetanus vaccine are recommended every ten years. Protection can be verified by measuring the antitoxin level in the blood. Diphtheria can be prevented in those exposed as well as treated with the antibiotics erythromycin or benzylpenicillin. A tracheotomy is sometimes needed to open the airway in severe cases. In 2015, 4,500 cases were officially reported worldwide, down from nearly 100,000 in 1980. About a million cases a year are believed to have occurred before the 1980s. Diphtheria currently occurs most often in sub-Saharan Africa, India, and Indonesia. In 2015, it resulted in 2,100 deaths, down from 8,000 deaths in 1990. In areas where it is still common, children are most affected. It is rare in the developed world due to widespread vaccination but can re-emerge if vaccination rates decrease. In the United States, 57 cases were reported between 1980 and 2004. Death occurs in 5% to 10% of those diagnosed. The disease was first described in the 5th century BC by Hippocrates. The bacterium was identified in 1882 by Edwin Klebs.
