Despite a steady decline in reported cases following a large outbreak in 2022, diphtheria continues to be detected in Europe, with case numbers still exceeding pre-2020 levels. A Rapid Risk Assessment published today by the ECDC warns that ongoing transmission of diphtheria caused by Corynebacterium diphtheriae may impact certain population groups that are more vulnerable to infection and calls for targeted public health measures to protect those at greatest risk.
Since January 2023, a total of 234 diphtheria cases have been reported across the European Union and European Economic Area (EU/EEA). Many of these infections have occurred in groups facing higher exposure risks, including people experiencing homelessness, individuals living, working, or volunteering in temporary accommodation centres, migrants, and people who use or inject drugs. Before 2020, the EU/EEA recorded an average of just 21 cases of diphtheria annually. In 2022, 320 cases were reported, primarily among newly arrived migrants who were exposed during transit. Most infections were linked to three sequence types: ST377, ST384, and ST574.
Since late 2022, six European countries — Austria, Czechia, Germany, Norway, Poland, and Switzerland — have reported 82 diphtheria cases linked to one of these outbreak-related sequence types. At least 25 of these cases were identified among people experiencing homelessness, individuals who use or inject drugs, unvaccinated persons, and older adults.
Although widespread vaccination coverage keeps the risk to the general population very low, the ECDC notes that the risk remains moderate for groups with increased vulnerability. People who are unvaccinated can develop skin infections or, more severely, respiratory diphtheria, which can be fatal in 5–10% of cases. In communities with high vaccination coverage, most diphtheria infections tend to be mild or asymptomatic, and fully vaccinated individuals rarely develop the disease. Vaccination against diphtheria remains a standard part of national immunisation programmes throughout Europe.
Because diphtheria is now relatively rare and can present in multiple ways, healthcare providers may struggle to recognise and diagnose it promptly. The ECDC stresses the importance of improving awareness among clinicians and professionals working with high-risk groups to ensure cases are detected, properly treated, and reported to public health authorities.
To help minimise severe infections among vulnerable populations and limit the spread of C. diphtheriae within communities, the ECDC recommends the following measures:
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Raise awareness among healthcare professionals and those supporting at-risk groups about the different ways diphtheria can present.
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Conduct health promotion initiatives that are tailored to populations at greater risk and encourage their active participation.
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Guarantee equal access to vaccination by offering immunisations to groups with higher susceptibility to infection.
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Regularly review local and national supplies of diphtheria antitoxin (DAT) to ensure effective treatment is available.
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Strengthen surveillance systems to detect cases quickly and monitor transmission trends.
