diphtheria

Diphtheria is an acute bacterial infection caused primarily by Corynebacterium diphtheriae. It most often affects the upper respiratory tract, especially the nasopharynx and oropharynx, but cutaneous forms can occur. The disease is transmitted mainly through respiratory droplets or direct contact with respiratory or cutaneous lesions, and individuals are most contagious during symptomatic periods and for several days after starting treatment.

The illness is driven by diphtheria toxin, produced by toxigenic strains that carry a beta-prophage. The toxin inhibits protein synthesis, leading to local tissue necrosis and the formation of a thick pseudomembrane over the tonsils, pharynx, or nose. In severe cases the pseudomembrane can obstruct the airway. Systemic toxin can cause myocarditis, neuritis, and neuropathies. Clinical signs include sore throat, fever, malaise, and neck swelling (often referred to as a “bull neck” in severe cases).

Diagnosis is suggested by the appearance of a pseudomembrane and confirmed by laboratory testing. Cultures on tellurite-containing media, Gram stain, and antigen or molecular tests (PCR for the toxin gene) are used; the Elek test may demonstrate toxin production.

Treatment requires rapid administration of diphtheria antitoxin to neutralize circulating toxin, followed by antibiotics (typically erythromycin or penicillin) to eradicate the organism and reduce transmission. Airway support and isolation are important in severe cases.

Prevention relies on vaccination with diphtheria toxoid as part of the DTaP series for children and Tdap boosters for adolescents and adults. High vaccination coverage reduces transmission and provides herd protection. Global disease burden persists in areas with low vaccination coverage and limited health resources.