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What is Diphtheria?

Updated February 11, 2023

Diphtheria is a rare toxin-mediated respiratory disease caused by the bacterium Corynebacterium diphtheriae (C. diphtheriae), an aerobic gram-positive bacillus. The production of the toxin only occurs when C. diphtheriae is affected by the specific virus which contains the genetic toxin information. When this happens, the serious disease will occur. There are four different types (biotypes) of C. diphtheriae – belfanti, gravis, intermedius, and mitis. All strains can cause toxin production that can lead to serious disease. 

Diphtheria causes a gray-green to black, thick fiber-like covering (pseudomembrane) in the back of the throat and on the tonsils. The pseudomembrane can restrict breathing and swallowing. Additional symptoms of the disease include swelling of the lymph nodes in the neck, sore throat, weakness, malaise, fever, and chills.  If the toxins enter the bloodstream, additional complications may occur, including neuritis, myocarditis, proteinuria, pneumonia, thrombocytopenia, and death. 

Diphtheria is contagious and is spread from person to person through respiratory secretions (coughing, sneezing). It can also be transmitted if a person touches a wound of a person with diphtheria, or from touching objects contaminated with the bacteria. Vaccinated individuals are still able to spread the bacteria because vaccination does not eliminate carriage of Corynebacterium diphtheriae in the back of the throat or on the skin. 

The incubation period of diphtheria ranges from one to 10 days but is generally between two and five days. The disease can affect any mucus membrane in the body, and symptoms will differ depending on the site. Areas that can be infected include the skin (cutaneous), anterior nasal passages, tonsils and pharynx, larynx, eye (ocular), external ear canal, and genitals.  Certain strains of diphtheria do not produce toxins and will generally result in mild to moderate inflammation of the throat.  Diphtheria can reoccur in individuals who have already had the disease. 

Cutaneous diphtheria is common in persons who reside in tropical countries. In the U.S., it is usually found among persons experiencing homelessness, and the strains are generally not toxin-producing. These infections typically present as ulcers or a scaling rash.  In 2019, the CDC updated their case definition of diphtheria to include cases of cutaneous diphtheria.  However, as of March 2021, no adequate data is available on the prevalence of cutaneous diphtheria in the United States. 

C. diphtheriae is exclusive to humans, and most who have it are asymptomatic. The disease is extremely rare in U.S. and other developed countries with good sanitation.  Between 1996 and 2017, there were 13 reported cases of respiratory diphtheria in the U.S. – five confirmed through culture and eight considered probable, as culturing was not completed. Of those cases, one fatality occurred in an international traveler who returned from an area where diphtheria is considered endemic. 

Globally, in 2017, there were 8,819 cases of diphtheria reported worldwide. 

IMPORTANT NOTE: NVIC encourages you to become fully informed about Diphtheria and the Diphtheria vaccine by reading all sections in the Table of Contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.

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