Autochthonous outbreak of respiratory diphtheria caused by Corynebacterium diphtheriae, Germany, September 2024.

In September 2024, a school-aged child (P1), unvaccinated against diphtheria, was hospitalised with severe respiratory diphtheria caused by toxigenic Corynebacterium diphtheriae. P1 subsequently died from the disease. The child's mother (P2) had pharyngitis 9 days before the onset of symptoms of P1 and subsequently tested positive for C. diphtheriae. In multilocus sequence typing (MLST), the C. diphtheriae isolates from P1 and P2 were of sequence type (ST) 574. In core genome (cg)MLST, they were clonal, suggesting recent human-to-human transmission. This indicates the first autochthonous respiratory diphtheria outbreak by toxigenic C. diphtheriae in Germany since 1984 with epidemiologically- and molecularly-confirmed transmission. Furthermore, the isolates were close to isolates from patients with cutaneous diphtheria among people experiencing homelessness in two major German cities in 2023 and 2024, and to isolates from an outbreak among newly arriving migrants across several European countries, including Germany, detected in 2022. This indicates transmission beyond vulnerable groups. Our findings illustrate the potential of C. diphtheriae spreading further from patients with cutaneous diphtheria and even causing outbreaks of respiratory diphtheria. Given the potentially serious complications of respiratory diphtheria, including death, equitably achieving and maintaining high vaccination coverage among the whole population, especially among vulnerable people is essential.