Surveillance of diphtheria in the Netherlands between 2000–2021: cutaneous diphtheria supersedes the respiratory form.

Background: Diphtheria is a severe respiratory or cutaneous infectious disease, caused by exotoxin producing Corynebacterium diphtheriae, C. ulcerans and C. pseudotuberculosis. Diphtheria is once again prevalent due to breakdown of immunisation programmes, social disruption and unrest. Aim: This study describes the notified diphtheria cases in the Netherlands between 2000–2021 and isolates that were sent to the National Institute for Public Health and the Environment (RIVM). Methods: File investigation was performed including all notified cases and isolates of C. diphtheriae, C. ulcerans and C. pseudotuberculosis that were tested for toxin production using a toxin-PCR and Elek test. An exploratory review was performed to understand transmission in populations with a high vaccination uptake. Results: Eighteen diphtheria notifications were made with confirmed toxigenic C. diphtheriae (n = 9) or ulcerans (n = 9) between 2000 and 2021. Seventeen (94.4%) presented with a cutaneous infection. All cases with a suspected source abroad (n = 8) concerned infection with C. diphtheriae. In contrast, 9/10 cases infected in the Netherlands were caused by C. ulcerans, a zoonosis. Secondary transmission was not reported. Isolates of C. ulcerans sent to the RIVM produced more often the diphtheria exotoxin (11/31; 35%) than C. diphtheriae (7/89; 7.9%). Conclusion: Both human-to-human transmission of C. diphtheriae and animal-to-human transmission of C. ulcerans rarely occurs in the Netherlands. Cases mainly present with a cutaneous infection. Travel-related cases remain a risk for transmission to populations with low vaccination coverage, highlighting the importance of immunization and diphtheria control measures. [ABSTRACT FROM AUTHOR]