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Diphtheria is an acute infection caused by Corynebacterium diphtheriae. The incidence of diphtheria is inversely related to the percentage of immune individuals in an area, and it remains endemic in countries without effective immunization programs. The incidence of diphtheria in the United States has declined dramatically since aggressive immunization efforts were begun in 1980. Concurrently, diphtheria shifted from a disease of children to a disease of adults with waning immunity. The potential for outbreaks continues, however, if segments of a community are not immunized.


C diphtheriae is an irregularly staining, non–spore-forming, nonmotile, unencapsulated, gram-positive bacillus. Metachromatic granules and a cuneiform appearance help distinguish the organism on smear. There are 4 biotypes (ie, mitis, intermedius, gravis, belfanti) that are differentiated by colony morphology, growth characteristics, and biochemical reactions. All biotypes are capable of producing a cytotoxic exotoxin that inhibits protein synthesis in host cells. The ability of a strain to produce the exotoxin is conferred by a lysogenic bacteriophage that carries the gene for toxin production. The toxin leads to the formation of pseudomembranes in the pharynx and respiratory tract, as well as systemic toxicity including myocarditis and polyneuropathy. C diphtheriae also presents as a cutaneous infection that often is associated with homelessness and tropical areas.

C diphtheriae inhabits mucosal epithelial cells (primarily respiratory tract) and skin of humans, the only reservoir. Transmission occurs from person-to-person by respiratory droplets and close contact with respiratory secretions or discharge from cutaneous lesions. Diphtheria occurs worldwide, and it may present at any time of the year, although it is most common during winter. Because humans are the only significant reservoir, closeness and duration of contact with an ill person or a healthy carrier are important determinants of infection spread. As a result, attack rates in households and in crowded living conditions are high.


The presentation of diphtheria depends on the primary site of infection. Respiratory tract diphtheria is characterized by either membranous nasopharyngitis or obstructive laryngotracheitis. Cutaneous diphtheria is associated with infected skin lesions that lack a characteristic appearance. With either presentation, toxin produced by the organism results in further symptoms.


After an average incubation period of 2 to 4 days, symptoms of a sore throat with mild pharyngeal injection and low-grade fever develop. Systemic signs of illness are absent in the early stages. Within 1 to 2 days, areas of yellow or “dirty” white exudate appear, most frequently on or adjacent to the tonsils. Subsequently, these areas coalesce to form a light reflective, sharply outlined pseudomembrane. The pseudomembrane consists of necrotic epithelium embedded in an inflammatory, organized exudate at the surface. Inflammatory changes in the underlying epithelium may extend into the submucosa and induce hemorrhage. Dislodgement of the pseudomembrane exposes an edematous, bleeding submucosa. The organisms remain in ...

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