Since the beginning of 2022, several cases of diphtheria have been reported in nine regions of mainland France, as well as in Mayotte and Réunion. Compared to other years, the number of cases of C. diphtheriae is significantly higher than average. In mainland France, the majority of cases were reported among migrants and travelers. Thanks to very high vaccination coverage over many years, the occurrence of severe cases or clusters within the general population appears extremely low in mainland France and Réunion. In Mayotte, where vaccination coverage is insufficient, the bacterium has been circulating for several years.

Santé publique France is monitoring the evolving situation and the increase in diphtheria cases among migrants, the vast majority of whom are not up to date on their vaccinations. A reminder of vaccination and care recommendations has been sent to associations and healthcare professionals.

Situation Update in France

As of November 30, 2022, 55 cases of diphtheria have been reported in France since the beginning of the year (Figure 1):

• 8 cases of diphtheria caused by Corynebacterium ulcerans (C. ulcerans) in mainland France;

• 30 cases of diphtheria caused by Corynebacterium diphtheriae (C. diphtheriae) in mainland France;

• 13 cases of diphtheria caused by C. diphtheriae in Mayotte and 4 in Réunion.

In 2022, compared to the previous 5 years, the number of C. ulcerans diphtheria cases was similar (an average of 7.2 cases per year), but the number of C. diphtheriae diphtheria cases was significantly higher than the average observed at that time (metropolitan France: 3.4 cases per year over the past 5 years; Mayotte: 2.6 cases per year over the past 5 years; Réunion: 0.6 cases per year over the past 5 years).

In mainland France

The majority of cases were reported among migrants (n=24) but also among travelers (n=5) (Figure 2). For these 29 cases, a link was found to one or more of the following countries: Afghanistan (n=21), Turkey (n=6), Italy (n=5), Serbia (n=5), Austria (n=4), Tunisia (n=3), Bulgaria (n=2), Iran (n=2), Hungary (n=2), Mali (n=2), Switzerland (n=2), Slovenia (n=1), Syria (n=1), Senegal (n=1), Thailand (n=1). When the date of their arrival in France was known (n=9), it was less than 15 days prior to the date of disease notification.

Furthermore, one case was likely infected on French soil through contact with a person returning from a trip to Togo.

Cases of diphtheria caused by C. diphtheriae were predominantly men (n=28), aged 11 to 47 years (average age 21). Only two of them were up to date on their diphtheria vaccinations. For 24 of them, vaccination status was unknown.
Among the cases occurring in migrants, 6 were residing in shelters.

Cases were diagnosed in 9 regions. The Normandy region was the most affected, with 7 reported cases (Figure 3). Twenty-five cases were cutaneous forms, 3 were asymptomatic carriers (in the oropharynx), one was a mildly symptomatic respiratory form (autochthonous case), and another presented with symptoms of classic respiratory diphtheria (migrant).

Two clusters were reported: one involved 4 cases who had traveled together on a bus, and the other involved two cases who had traveled together.

Genotyping of 19 isolates by the National Reference Center (NRC) for Corynebacteria of the diphtheriae complex via genomic sequencing revealed 5 distinct genetic groups: ST377a (2 cases), ST377b (1 case), ST384 (2 cases), ST574 (3 cases), ST698 (2 cases). These groups have also been identified in other European countries. The remaining isolates are currently being sequenced.

This increase in the number of cases among migrants is also being observed in other European countries. As of September 26, 2022, the European Centre for Disease Prevention and Control (ECDC) reported 92 cases of diphtheria caused by C. diphtheriae in 2022 across seven European countries (Germany, Austria, Belgium, France, Great Britain, Norway, and Switzerland)

Mayotte and Réunion

In Mayotte, local circulation of the bacterium has been known for several years. In 2022, of the 13 reported cases, 7 were cutaneous forms, 1 was an ENT form, and 5 were asymptomatic carriers (ENT) of the bacterium. These last 5 infections were detected among close contacts of 2 symptomatic cases. One death occurred in an unvaccinated 7-month-old infant.

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In Réunion, during the 2021–2022 period, all reported cases were imported cases. In 2022, 4 cases were reported, and no travel history was identified. These 4 cases were apparently unrelated and were cutaneous forms.

Genomic clustering analysis by the CNR showed that 12 strains (8 in Mayotte and 4 in Réunion) shared the same characteristics, strongly suggesting that these cases are linked. We have no hypothesis at this stage regarding the nature of this link.