Diphtheria Has Not Disappeared: Why Experts Are Warning About a Dangerous Comeback

Diphtheria is an infectious disease caused by the bacterium Corynebacterium diphtheriae. The source of infection is always a human being—someone who is ill, recovering from the disease, or an asymptomatic carrier.

The infection spreads primarily through respiratory droplets. The bacteria usually enter the body through the mouth or nose, and less frequently through damaged skin or other mucous membranes. As a result, the most common forms of the disease affect the throat (pharynx), larynx and nose. More rarely, diphtheria may involve the conjunctiva, middle ear or skin.

The Hallmark Sign of Diphtheria

The most characteristic feature of diphtheria is the formation of grayish, tightly adherent coatings on the tonsils, throat or nasal mucosa. These so-called pseudomembranes are difficult to remove and are considered a classic sign of the disease.

Typical symptoms include sore throat, fever, weakness and enlarged lymph nodes. Other possible symptoms include foul-smelling breath, difficulty swallowing or breathing, drooling and apathy.

In severe cases, extensive swelling of the throat and neck may develop, sometimes referred to as a “bull neck.” Diphtheria can lead to serious complications because C. diphtheriae produces diphtheria toxin, which can damage the heart, nervous system and kidneys.

How the Bacteria Become Dangerous

The disease develops when a person is infected with toxin-producing strains of C. diphtheriae. The ability to produce toxin arises when the bacterium itself becomes infected by a bacteriophage—a virus that infects bacteria.

C. diphtheriae is a Gram-positive, non-spore-forming bacillus first isolated in 1884 by Friedrich Loeffler.

Non-toxin-producing strains rarely cause disease. Importantly, other bacteria, including Corynebacterium ulcerans and Corynebacterium pseudotuberculosis, can also acquire toxin-producing bacteriophages. When this occurs, they may cause illnesses similar to diphtheria.

While humans are the only reservoir for C. diphtheriae, these other species may be transmitted from animals, including household pets.

Vaccination Dramatically Reduced Global Cases

According to estimates from the World Health Organization (WHO), increasing diphtheria vaccination coverage from 24% in 1980 to more than 70% in 1990 reduced annual global cases from approximately 98,000 to around 9,000.

In later years, as vaccination rates reached roughly 85% of the population, the number of reported cases fell even further to about 4,200 annually.

In Poland, no diphtheria cases were recorded between 1997 and 2024. However, the disease reappeared in 2025, first in a child returning from a vacation in Zanzibar and later in an adult who had contact with the child in a hospital in Wrocław.

In regions where diphtheria remains endemic, bacterial carriage may affect as much as 3–5% of the population.

Incubation Period and Infectiousness

The incubation period typically lasts between 2 and 4 days but can extend up to 10 days.

People can spread the infection during the final two days of incubation, throughout the entire symptomatic period and for up to four days after symptoms resolve if appropriate treatment is given. In untreated individuals, contagiousness may persist for 2 to 3 weeks.

Why Booster Vaccinations Matter

Today, vaccination remains the most effective way to prevent diphtheria. During the first half of the 20th century, the disease was one of the leading causes of death among children.

The situation changed dramatically after the introduction of mandatory vaccination programs, most commonly administered in combination with protection against tetanus and whooping cough.

Paradoxically, the success of vaccination has contributed to lower public awareness of the disease. Increasing numbers of people are refusing vaccines or failing to receive recommended booster doses.

Importantly, immunity against diphtheria does not last for life. Regular booster vaccinations are necessary, particularly for adults.

Treatment Requires Hospital Care

Diphtheria treatment is always provided in a hospital setting. The cornerstone of therapy is the rapid administration of diphtheria antitoxin together with appropriate antibiotics.

Early antitoxin treatment is critical because it neutralizes circulating toxin before it can damage tissues. Antibiotics play a supportive role by eliminating the bacteria and reducing transmission.

In severe cases, especially when the larynx is affected, intubation or tracheotomy may be required to maintain the airway and save the patient's life.

Patients should remain in isolation until two respiratory cultures obtained 24 hours apart after completing antibiotic treatment are confirmed negative.

A Preventable Disease That Has Not Disappeared

Although diphtheria has become rare in many countries thanks to widespread vaccination, it has not been eradicated. The disease remains present in some parts of the world and can quickly re-emerge when vaccination coverage declines.

Health experts emphasize that maintaining routine immunization and receiving recommended booster doses remain the most effective ways to prevent outbreaks and protect vulnerable populations from this potentially life-threatening infection.

Source: Collective work, Interna Szczeklika 2023, Medycyna Praktyczna, Kraków 2023.