<i>Corynebacterium diphtheriae</i> Outbreak in Migrant Populations in Europe.

Abstract

A surge of cases of <i>Corynebacterium diphtheriae</i> infection was observed in reception centers for migrants in Europe beginning in the summer of 2022. Most of the cases were cutaneous, although some respiratory cases as well as one death were reported. A pan-European consortium was created to assess the clinical, epidemiologic, and microbiologic features of this outbreak. We assessed cases of toxigenic <i>C. diphtheriae</i> infection that were reported in 10 European countries from January through November 2022. Data regarding countries of origin and transit routes were obtained from interviews with the patients. Whole-genome sequencing and antimicrobial-susceptibility testing were performed on bacterial isolates that were obtained from the patients. The phylogenetic relationships of the isolates and their antimicrobial-resistance genes were evaluated. A total of 363 toxigenic <i>C. diphtheriae</i> isolates were identified among 362 patients during the study period. Clinical data were available for 346 patients (95.6%): 268 (77.5%) had cutaneous diphtheria, 53 (15.3%) had respiratory diphtheria (11 [3.2%] had a pseudomembrane), and 9 (2.6%) had both respiratory and cutaneous symptoms. Four major genetic clusters were identified, which indicated the multiclonal nature of the outbreak. The <i>ermX</i> gene (which codes for erythromycin resistance) and the <i>pbp2m</i> and <i>blaOXA-2</i> genes (which code for beta-lactam resistance) were detected in a subgroup of isolates. Isolates that carried <i>ermX</i> were resistant to erythromycin, and isolates that carried <i>pbp2m</i> were resistant to penicillin but were susceptible to amoxicillin. On the basis of the genomic variation within the four genetic clusters, their most recent common ancestors were estimated to have existed between 2017 and 2020. The distribution of each genetic cluster of <i>C. diphtheriae</i> isolates across multiple countries in Europe showed repeated cross-border spread. The large number of <i>C. diphtheriae</i> infections among migrants is a cause for concern, particularly given that antimicrobial-resistance phenotypes threaten the efficacy of first-line treatments. (Funded by the Bavarian State Ministry of Health, Care, and Prevention and others.).