The differential diagnosis includes infectious mononucleosis, adenovirus or herpes simplex infection, Vincent's angina, pharyngitis due to Arcanobacterium haemolyticum, candidiasis, streptococcal tonsillitis, and acute epiglottitis. The tonsillar exudate of infectious mononucleosis is creamy in color, does not extend beyond the tonsil, and does not produce bleeding if removed. Streptococcal pharyngotonsillitis is associated with more severe local symptoms and a higher fever. Epiglottitis is acute in onset and is not associated with a local membrane. In the head and neck, diphtherial neuropathy usually involves the cranial nerves, causing diplopia, slurred speech, and dysphagia.
C. diphtheria colonizes the human respiratory tract alone. Isolation of the organism occurs on specialized growth media including potassium tellurite (Tinsdale agar) to inhibit other oral flora. Treatment is reserved for patients carrying toxigenic strains, identified by streaking of the organism and controls on toxin-antibody impregnated paper and observing for immunoprecipitation lines. Polymerase chain reaction (PCR) may also be used to detect toxin genes.
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