Toxigenic Corynebacterium diphtheriae (C. diphtheria) and occasionally, toxigenic Corynebacterium ulcerans (C. ulcerans).
C. diphtheriae typically resides in the upper respiratory tract and is transmitted from person to person through droplets and close physical contact. Transmission is facilitated by crowding and poor socioeconomic conditions. A cutaneous form of diphtheria caused by C. ulcerans is common in tropical countries. This bacterium is easily transmitted by close contact. Chronic carriage of C. diphtheria and C. ulcerans occurs frequently.
Nature of the disease
Diphtheria is caused by a potent bacterial toxin that can produce obstructive pseudo-membranes in the upper respiratory tract (croup) or damage to the myocardium and other tissues. Although asymptomatic or mild infections are most common, untreated diphtheria may be severe and sometimes fatal. C. ulcerans can cause respiratory or cutaneous diphtheria in non-immunized individuals and cutaneous, mostly non-toxic lesions even in fully vaccinated individuals.
Diphtheria is found worldwide, although it is not common in industrialized countries because of long-standing routine use of diphtheria/tetanus/pertussis (DTP) vaccine. Large epidemics occurred in several east European countries in the 1990s.
Risk for travellers
Non-immunized or incompletely immunized travellers have occasionally contracted diphtheria when visiting endemic areas. The disease occurs more frequently in parts of the world where DTP coverage is low.