Diphtheria is an infectious disease caused by the bacterium Corynebacterium diphtheriae, which primarily infects the throat and upper airways (respiratory diphtheria), and produces a toxin affecting other organs.

Diphtheria is transmitted from person to person through close physical and respiratory contact. The incubation period for respiratory diphtheria is 2-5 days [1-3]. Diphtheria has an acute onset and the main characteristics are sore throat, low fever and swollen glands in the neck. The toxin may, in severe cases, cause myocarditis or peripheral neuropathy. The diphtheria toxin causes a membrane of dead tissue to build up over the throat and tonsils, making breathing and swallowing difficult [4]. Diphtheria can be fatal [1]. In regions with temperate climates, most cases occur during the cold season, whereas in warmer climates transmission takes place throughout the year.

Treatment of diphtheria includes diphtheria antitoxin and antibiotics [1].

Throughout history, diphtheria has been one of the most feared infectious diseases globally, which caused devastating epidemics, mainly affecting children. During major diphtheria epidemics in Europe and the USA in the 1880s, the case-fatality rates of respiratory diphtheria reached 50% in some areas. Case-fatality rates in Europe had dropped to about 15% during the First World War, mainly as a result of widespread use of diphtheria antitoxin (DAT) treatment. Diphtheria epidemics also ravaged Europe during the Second World War, causing about 1 million cases and 50,000 deaths in 1943 [5].

Inactivation of the toxin allows for production of an inoffensive diphtheria toxoid. Diphtheria toxoid-based vaccines became available in the late 1940s in Europe and North America and were shown to reduce outbreaks in vaccinated populations [5]. Diphtheria remains a significant health problem in some ten countries with poor routine vaccination coverage. The annual number of reported cases of diphtheria remained relatively unchanged between the early 2000s and 2017, (fewer than 10,000 reported cases annually) [6]. Since then of the numbers have increased (17,000 in 2018 and 23,000 in 2019) due to outbreaks.

For more details please see the WHO disease description for Diphtheria.