No 21 - 2025

Possible outbreak of diphtheria in Germany

The German health authorities have reported a possible outbreak of diphtheria with cases spread around the country. Since January 1, 2022, a total of 126 cases with laboratory-confirmed diphtheria have been detected, all belonging to the same bacterial strain (ST-574) of Corynebacterium diphtheriae. There were 55 cases detected in 2022, 49 cases in 2023, and 18 cases in 2024. In 2025, five cases were detected up until May 16.

From January 1, 2024 until now, in which 23 cases with genotype ST-574 have been detected, two genetic subgroups (sub-clusters) have emerged among persons with non-immigrant backgrounds.

The 18 cases have been cutaneous diphtheria and five cases respiratory diphtheria, among which three patients have died. Among the three deceased were an unvaccinated child and two elderly persons with uncertain vaccination status. For comparison, in 2020 and 2021 there were a total of three cases of respiratory diphtheria in Germany, and no deaths.

In all cases, it is an infection with toxin-producing diphtheria bacteria, which especially in the respiratory form can be serious and possibly fatal. For further information about the disease diphtheria, refer to SSI’s disease encyclopedia  (in Danish).

The first many cases of especially cutaneous diphtheria were detected among migrants and asylum seekers from Afghanistan, among others. In the later part of the period, there appears to have arisen two subgroups of infected persons, primarily among non-migrants. A group of primarily infected homeless persons, including homeless drug users, has been identified in and around Frankfurt, where genetic typing of bacterial isolates has been traced back to detected bacterial strains among migrants in 2022. These cases belong to the first genetic sub-cluster. Another group of infected with cutaneous diphtheria has been detected among the homeless in Berlin, and additional cases of respiratory diphtheria have been found in four other states. These cases belong to the second sub-cluster.

Since the beginning of 2025, 10 cases of diphtheria caused by C. diphtheriae have been reported through EpiPulse in the EU/EEA countries: five from Germany, two from Belgium, one from Austria, and one from Latvia.

Diphtheria in Denmark

Diphtheria is a rare infection in Denmark. This is due to the fact that the vast majority are vaccinated, partly through the childhood vaccination program, but also in connection with wound injuries, where a tetanus vaccine, which also contains protection against diphtheria (diTeBooster), is given if needed. All persons in Denmark are recommended to receive a booster vaccination against diphtheria every 10 years.

Since 2020, only a single case of diphtheria in the form of cutaneous diphtheria in a chronic wound in a person with another chronic condition has been detected. This was a toxin-producing strain of a special diphtheria bacterium, Corynebacterium ulcerans. In addition, one person has been treated with antitoxin due to suspicion of respiratory diphtheria, but the suspicion could not be diagnostically verified. The person had returned from an overseas trip from an area where diphtheria occurs.

Increased awareness of the diagnosis

Based on the current situation in Germany and the close geographical proximity to Denmark, doctors are encouraged to increase awareness of diphtheria, especially in the occurrence of possible chronic wounds that do not respond to treatment with antibiotics among recently arrived migrants or asylum seekers, homeless persons, drug users, elderly persons with chronic weakness, and especially if there is missing or uncertain vaccination against diphtheria. In case of clinical suspicion of diphtheria or findings of diphtheria bacteria at the local Department of Clinical Microbiology and need for clarification of whether these are toxin-producing, doctors can contact the diagnostic call center at SSI at 3268 8600 during daytime hours. Outside normal working hours, the on-call infectious disease epidemiologist can be contacted at 4131 7404. The latter must also be contacted when considering the need for treatment with diphtheria antitoxin, which is dispensed from SSI based on specific indication.

Reference is also made to the Danish Health Authority’s guidelines for the handling of diphtheria (in Danish), including the handling of close contacts to suspected or confirmed cases.

(P.H. Andersen, Department of Infectious Disease Epidemiology and Prevention, A. Ronayne, Bacteria, Parasites and Fungi)