Toxigenic Corynebacterium diphtheriae and toxigenic C. ulcerans.
Transmission of bacteria typically residing in the upper respiratory tract is from person to person, through droplets and close physical contact, and is increased in overcrowded and poor socioeconomic conditions. A cutaneous form of diphtheria caused by Corynebacterium ulcerans is common in tropical countries and may also be an important source of infection for pharyngeal diphtheria.
Nature of the disease
The infection commonly affects the throat and may lead to obstruction of the airways and death. There is toxin-induced damage to organs such as the heart. Nasal diphtheria may be mild, and chronic carriage of the organism frequently occurs; asymptomatic infections are common.
Diphtheria is found worldwide, although it is not common in industrialized countries because of long-standing routine use of DTP vaccine. Large epidemics occurred in several east European countries in the 1990s.
Risk for travellers
Potentially life-threatening illness and severe, lifelong complications are possible in non-immunized or incompletely immunized individuals. Diphtheria is more frequent in parts of the world where vaccination levels are low.