Diphtheria Outbreak among Persons Experiencing Homelessness, 2023, Linked to 2022 Diphtheria Outbreak, Frankfurt am Main, Germany.

After 3 cases of Corynebacterium diphtheriae infection associated with intravenous drug use among persons experiencing homelessness (PEH) were reported to the Health Protection Authority in Frankfurt am Main, Germany, in 2023, we examined pathogen spread among PEH. Furthermore, we investigated a possible link with the 2022 outbreak of diphtheria in Europe. From swab samples collected during August-November 2023 from 36 PEH and cutaneous lesions, we detected 3 additional cases of cutaneous toxigenic C. diphtheriae. Sequence type 574 was identified in 5 case-isolates and is genetically associated with 1 of the predominant clusters in identified in the 2022 outbreak. Our findings demonstrate the need for increased detection and monitoring of cutaneous diphtheria and boosting immunity against diphtheria in groups with increased risk for infection. Genomic analyses are valuable for identifying genetic relationships between outbreaks, even when epidemiologic data are scarce.