Diphtheria cases on the rise in Western Europe since 2022

The largest diphtheria epidemic in Western Europe in seventy years has been affecting vulnerable populations – such as migrants and homeless people – since 2022, the Pasteur Institute and Public Health France warned on Wednesday, June 4, calling for increased vigilance and targeted action.

Diphtheria is a highly contagious bacterial infection that attacks the respiratory tract in its most severe, sometimes fatal, form, or the skin. However, an unusual spike in cases of infections by a bacterium responsible for diphtheria (Corynebacterium diphtheriae) was observed in 2022 in several European countries, mainly among recent migrants, according to researchers and epidemiologists from Pasteur and Public Health France, who published a study on the subject in The New England Journal of Medicine . That year, 362 cases were recorded by the European Centre for Disease Prevention and Control.

Rapid measures (contact tracing and screening for secondary cases) have helped mitigate the epidemic, but rare infections have been observed so far among migrants and other vulnerable populations, including the homeless, the scientists note. A total of 536 cases, including at least three deaths, have been recorded in Europe since 2022.

Analysis of samples from 362 patients in ten countries showed that 98% were men, with a median age of 18, almost all of whom had recently migrated. While the majority of infections (77%) were cutaneous, 15% were respiratory.

Above all, "the epidemic, which has mainly affected migrant populations from Afghanistan and Syria, does not result from initial contamination in these countries of origin, but during migratory journeys or in places of accommodation in European countries," summarizes a press release.

Given the very close genetic proximity between the bacterial strains observed in people from different countries, scientists hypothesize that "a recent point of contact, outside the country of origin, allowed the contamination."

However, there are still some unknowns, such as the geographical area and conditions of these contaminations. And a genetic link established between the strain that circulated in 2022 and an epidemic in 2025 in Germany suggests that "the bacteria continues to circulate quietly in Western Europe."

While they note the effectiveness of vaccination programs for the general population, experts call for increased vigilance and action: raising awareness among doctors and people in contact with these populations about the symptoms, vaccinations, appropriate antibiotic therapies, etc.

Diphtheria also poses a risk to the unvaccinated, injecting drug users, and the elderly with pre-existing illnesses, points out Isabelle Parent du Châtelet of the Pasteur Institute and Public Health France.