Unprecedented wave of diphtheria cases in Europe

It is a disease that one might think has disappeared, and yet: the year 2022 was distinguished by an unprecedented wave of imported cases of diphtheria, in France but also in several European countries. Diphtheria, caused by the bacterium Corynebacterium diphtheriae, is a highly contagious disease that is transmitted from person to person, through saliva, skin wounds and more rarely through objects soiled by patient secretions. Main manifestation: angina which can be complicated by cardiac or neurological damage and lead to death.

There has been a vaccine against diphtheria for almost a century, and the French population is largely covered thanks to compulsory vaccination. However, a handful of cases are recorded each year, imported by travelers or migrants. But they usually remain very limited.

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However, in 2022, France alone recorded 30 cases, other countries even more: 118 in Germany, 69 in Austria, 52 in Switzerland, lists a communication unveiled at the European Congress of Clinical Microbiology and Infectious Diseases. “It is a fairly exceptional situation, however we cannot speak of a European epidemic, because there have been no transmissions to the general population: these cases remain limited to people arriving from abroad, in a situation vulnerability, often asylum seekers", emphasizes Dr Sylvain Brisse, director of the National Diphtheria Reference Center and research director at the Institut Pasteur, who conducted the genomic analysis of the strains of the bacterium.

The causes of this sudden wave (but now over in France) are not really known, but experts assume that the phenomenon is linked to poor vaccination coverage in the countries from which the patients originate (men in their twenties years for the most part): mainly Afghanistan and Syria, destabilized by years of conflict. “The vaccine protects against the disease, but not against the asymptomatic carriage of the bacterium: it therefore continues to circulate. And, when the vaccination coverage of the population declines, we are witnessing the re-emergence of cases, ”explains Dr Brisse.

The forms of diphtheria observed were mainly cutaneous (therefore not very serious), "probably linked to a lack of hygiene and promiscuity", continues the expert. The patients were probably contaminated on the migratory routes or just before leaving. The genomic study conducted by Dr Brisse revealed four strains, "which suggests that there were four chains of transmission". It was also observed that some minority strains were resistant to macrolides. “It is a problem, because these antibiotics are used in patients allergic to amoxicillin or penicillin. »

“The message to take away from all of this is that these diseases that we no longer know about here can come back thanks to geopolitical imbalances, because they are not controlled in the countries of the South, recalls Sylvain Brisse. Let's never forget that germs know no borders: it is therefore essential to maintain good vaccination coverage on our territory. This is particularly effective in France, because our recommendations provide for booster shots in adults at 25, 45 and 65 years old, then every ten years, which is not the case in all countries. In Austria, for example, a study carried out on 16,000 volunteers in 2021 and 2022 and presented at this same microbiology congress showed that a third of the population was insufficiently immunized against diphtheria. The authors call for an intensification of the recall campaign among the oldest.