Diphtheria, a bacterial infection that has been eradicated in mainland France

Diphtheria, caused by the bacterium Corynebacterium diphtheriae, is a highly contagious disease transmitted from person to person. Its most serious consequences stem from the toxin it can produce. The bacterium carries the gene encoding the toxin (tox+). The main symptom of the disease is a sore throat, which can lead to complications such as heart or neurological damage and result in death. Thanks to very high vaccination coverage, diphtheria caused by Corynebacterium diphtheriae had been eradicated in mainland France between 1990 and 2010, with the exception of rare imported cases. The number of detected imported cases subsequently increased (up to 6 cases in 2019). The years 2022 and 2023 were marked by an epidemic among the migrant population, and since 2024, a few cases—likely contracted within mainland France and primarily affecting homeless individuals—have been regularly identified.

Surveillance for diphtheria was expanded in 2003 to include infections caused by other bacteria of the diphtheriae complex: Corynebacterium ulcerans, transmitted to humans through raw milk or pets, and Corynebacterium tuberculosis, transmitted by animals such as sheep or goats. These bacteria can also produce diphtheria toxin.

Diphtheria must be reported to the ARS whenever Corynebacterium diphtheriae, ulcerans, or pseudotuberculosis has been isolated and the toxin gene has been detected.

Diphtheria, a highly contagious infection

C. diphtheriae is transmitted directly through nasopharyngeal secretions or skin wounds and very rarely through indirect contact with objects contaminated by secretions from infected individuals. The incubation period ranges from 2 to 5 days.

C. ulcerans is transmitted primarily through contact with pets (especially cats and dogs) or through milk and contact with cattle. Human-to-human transmission has not been documented.

C. pseudotuberculosis is transmitted to humans by goats or sheep.

Vaccination

Vaccination against diphtheria is mandatory for infants. The primary vaccination series for infants consists of two injections at 2 and 4 months of age, followed by a booster at 11 months of age. Subsequent boosters are recommended at age 6, using a combination vaccine containing the acellular pertussis (Ac) component along with tetanus and diphtheria components at standard concentrations (DTP-Polio), then, between 11 and 13 years of age, with a combined vaccine containing reduced doses of diphtheria toxoid and pertussis antigens (dTcaPolio). Subsequently, adult boosters are now recommended at fixed ages of 25, 45, and 65, and then every 10 years (a 10-year interval starting at age 65, given immunosenescence), using a combined pertussis, tetanus, polio, and diphtheria vaccine with a reduced dose of toxoid (dTcaPolio). Vaccination is mandatory for healthcare professionals (booster shots administered at the same fixed ages—25, 45, and, depending on continued professional activity, 65—using a vaccine containing a reduced dose of diphtheria toxoid [dTcaPolio]) and is particularly recommended for travelers to endemic areas.

Regional Disparities

Widespread vaccination against diphtheria has led to the elimination of indigenous cases of diphtheria caused by C. diphtheriae in Western European countries. However, the disease remains a major public health problem in certain regions of the world, particularly in Africa, which serves as a source of imported cases for other countries. Since 2024, a few cases—likely contracted within mainland France and primarily affecting homeless individuals—have been regularly identified, particularly in the Île-de-France region.

Furthermore, Mayotte became the 101st French department in 2011. Since 2011, isolates of tox+ C. diphtheriae have been reported to health authorities.

This sporadic occurrence of diphtheria cases in Mayotte, mostly imported from the Comoros, necessitated an advisory from the HCSP regarding the adaptation of the protocol to follow when a case of cutaneous diphtheria occurs in the department of Mayotte.

• Cutaneous diphtheria: updated guidelines for Mayotte

Diphtheria, a disease primarily affecting the ENT system

The classic presentation caused by Corynebacterium diphtheriae is that of an ENT infection with diphtheritic tonsillitis, characterized by mild fever, varying degrees of dysphagia, pallor, and submandibular lymphadenopathy. The tonsils are covered with whitish, cream-colored, or grayish pseudomembranes that are highly adherent and may extend to varying degrees into the pharynx. Less typical presentations may occur, where the exudate suggests, in particular, infectious mononucleosis. Severe cases of diphtheria involve extensive, bleeding pseudomembranes. The infection may spread to the larynx, causing obstruction and asphyxia (croup). It may even affect the trachea and bronchi.

Cutaneous diphtheria is identified by the presence of pseudomembranes on a wound or a preexisting skin ulceration, which is often polymicrobial.

The severity of diphtheria, in addition to obstructive involvement of the respiratory tract, is linked to the spread of the diphtheria bacillus’s exotoxin into the myocardium and the nervous system.

C. ulcerans can also produce the same clinical presentations as C. diphtheriae, whereas C. pseudotuberculosis most often causes lymphadenitis.

Management with antibiotic therapy and serotherapy

The therapeutic management of a diphtheria case carrying the gene encoding the diphtheria toxin, in addition to specific treatment, includes antibiotic therapy, serotherapy, respiratory isolation in cases of ENT involvement, and updating vaccination status.
Prevention surrounding a case of diphtheria involves rapid detection of cases and their human contacts, followed by immediate management. Identifying animal contacts when C. ulcerans or pseudotuberculosis is detected and managing them is also strongly recommended.

Given the frequent occurrence of cases, particularly skin infections among migrants or homeless individuals, it is essential that healthcare professionals treating these populations systematically consider diphtheria when encountering an infected wound in these patients. Furthermore, their vaccination status should be verified and, if necessary, updated.