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Section 3. Summaries of Infectious Diseases

Diphtheria

Clinical Manifestations
Etiology
Epidemiology
Diagnostic Tests
Treatment
Isolation of the Hospitalized Patient
Control Measures

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CLINICAL MANIFESTATIONS

Respiratory diphtheria usually occurs as membranous nasopharyngitis or obstructive laryngotracheitis. Local infections are associated with a low-grade fever and gradual onset of manifestations over 1 to 2 days. Less commonly, diphtheria presents as cutaneous, vaginal, conjunctival, or otic infection. Cutaneous diphtheria is more common in tropical areas and among the urban homeless. Serious complications of diphtheria include severe neck swelling (bull neck) accompanying upper airway obstruction caused by extensive membrane formation, myocarditis, and peripheral neuropathies.


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ETIOLOGY

Diphtheria is caused by toxigenic strains of Corynebacterium diphtheriae; rarely, a diphtheria-like illness is caused by toxigenic strains of Corynebacterium ulcerans. C diphtheriae is an irregularly staining, gram-positive, nonspore-forming, nonmotile, pleomorphic bacillus with 4 biotypes (mitis, intermedius, belfanti, and gravis). All biotypes of C diphtheriae may be either toxigenic or nontoxigenic. Toxigenic strains express an exotoxin that consists of an enzymatically active A domain and a binding B domain, which promotes the entry of A into the cell. The toxin gene, tox, is carried by a family of related corynebacteria phages. The toxin inhibits protein synthesis in all cells, including myocardial, renal, and peripheral nerve cells, resulting in myocarditis, acute tubular necrosis, and delayed peripheral nerve conduction. Nontoxigenic strains of C diphtheriae can cause sore throat and other invasive infections, including endocarditis.


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EPIDEMIOLOGY

Humans are the sole reservoir of C diphtheriae. The organisms are spread by respiratory tract droplets and by contact with discharges from skin lesions. In untreated people, organisms can be present in discharges from the nose and throat and from eye and skin lesions for 2 to 6 weeks after infection. Patients treated with an appropriate antimicrobial agent usually are communicable for fewer than 4 days. . . . [Go to Full Text]