Diphtheria is usually transmitted by contact with respiratory droplets from infected persons or asymptomatic carriers. It can also be transmitted by contaminated objects or foods (such as contaminated milk). The incubation period is 2 to 5 days.
The bacteria primarily infect the nose and throat, although they may initially infect the skin, producing skin lesions. Corynebacterium diphtheriae produces a toxin that causes tissue damage (necrosis) in the immediate area of the infection, usually the nose and throat. It can also spread via the bloodstream to other organs, where it can cause significant damage. Although the toxin can damage any tissue, the heart and nervous system are most frequently and most severely affected. Localized infection in the throat and tonsillar area produces a characteristic membrane that is gray to black, tough, and fibrous. This membrane can cause airway obstruction.
Diphtheria may be mild and unrecognized or it may become progressive. If toxin enters the bloodstream, the patient may develop inflammation of the heart muscle (myocarditis), which is the most common and most worrisome complication. Toxic effects on the nervous system may also cause temporary paralysis.
The disease is now rare in many parts of the world because of widespread immunization. Risk factors include crowding, poor hygiene, and lack of immunization. The incidence of diphtheria in the U.S. is fewer than 5 cases per year. In 1993 and 1994, the states of the former USSR experienced a diphtheria epidemic, with more than 150,000 reported cases and 5,000 deaths. The epidemic was related to a drop in routine childhood DPT immunization to less than 60% of the population, failure to give booster doses to adults, and worsening economic conditions in the affected countries.
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