Toxigenic strains of Corynebacterium diphtheriae biotype mitis, gravis, intermedius, or belfanti.
Person-to-person through oral or respiratory droplets, close physical contact, and rarely, by fomites. Cutaneous diphtheria is common in tropical countries, and contact with discharge from skin lesions may transmit infection in these environments.
Endemic in many countries in Africa, South America, Asia, the South Pacific, the Middle East, and Eastern Europe and in Haiti and the Dominican Republic.
The incubation period is 2–5 days (range, 1–10 days). Affected anatomic sites include the mucous membrane of the upper respiratory tract (nose, pharynx, tonsils, larynx, and trachea [respiratory diphtheria]), skin (cutaneous diphtheria), or rarely, mucous membranes at other sites (eye, ear, vulva). Nasal diphtheria can be asymptomatic or mild, with a blood-tinged discharge.
Respiratory diphtheria has a gradual onset and is characterized by a mild fever (rarely >101°F [38.3°C]), sore throat, difficulty swallowing, malaise, loss of appetite, and if the larynx is involved, hoarseness. The hallmark of respiratory diphtheria is a pseudomembrane that appears within 2–3 days of illness over the mucous lining of the tonsils, pharynx, larynx, or nares and that can extend into the trachea. The pseudomembrane is firm, fleshy, grey, and adherent; it will bleed after attempts to remove or dislodge it. Fatal airway obstruction can result if the pseudomembrane extends into the larynx or trachea, or if a piece of it becomes dislodged.
A presumptive diagnosis is usually based on clinical features. Diagnosis is confirmed by isolating C. diphtheriae from culture of nasal or throat swabs or membrane tissue.
Patients with respiratory diphtheria require hospitalization to monitor response to treatment and manage complications. Equine diphtheria antitoxin (DAT) is the mainstay of treatment and is administered after specimen testing, without waiting for laboratory confirmation. In the United States, DAT is available to physicians under an investigational new drug protocol by contacting CDC at 770-488-7100.
An antibiotic (erythromycin or penicillin) should be used to eliminate the causative organisms, stop exotoxin production, and reduce communicability. Supportive care (airway, cardiac monitoring) is required. Antimicrobial prophylaxis (erythromycin or penicillin) is recommended for close contacts of patients.
All travelers should be up-to-date with diphtheria toxoid vaccine before departure. Routine booster doses with Td (tetanus-diphtheria) should be given to all adults every 10 years. This booster is particularly important for travelers who will live or work with local populations in countries where diphtheria is endemic.
CDC. Fatal respiratory diphtheria in a US traveler to Haiti—Pennsylvania, 2003. MMWR Morb Mortal Wkly Rep. 2004 Jan 9;52(53):1285–6.
CDC. Updated recommendations for use of tetanus toxoid, reduced diphtheria toxoid and acellular pertussis (Tdap) vaccine from the Advisory Committee on Immunization Practices, 2010. MMWR Morb Mortal Wkly Rep. 2011 Jan 14;60(1):13–5.
Galazka A. The changing epidemiology of diphtheria in the vaccine era. J Infect Dis. 2000 Feb;181 Suppl 1:S2–9.