Background and aim
Diphtheria is a notifiable disease caused by toxigenic Corynebacterium diphtheriae, that primarily involves mucus membranes of the upper respiratory tract (respiratory diphtheria) and non-healing ulcers (cutaneous diphtheria). Notifications are rare because of high vaccination rates with only 6 notifications in the Northern Territory (NT) between 2000-2024. However, in 2025 there were 9 notifications which followed a change in testing practices.
Methods and analysis
We described the epidemiology of diphtheria notifications in the NT in 2025 by age, sex, Indigenous status, specimen type, antibiotic susceptibilities, presenting complaint and vaccination status. We undertook contact tracing and public health action as per Queensland Health Guidelines for Public Health Units for Diphtheria. We described the number of contacts per case and cases identified through contact tracing. Outcomes There were 9 notifications; 8 (89%) were Aboriginal people; 6 (67%) were male, all were cutaneous with most 4 (44%) isolated from lower limb wounds. The median age was 40 years (range 16-60 years); 6 (67%) were hospitalised; none died. The median length of hospitalisation was 8 days (range 2 – 18 days); 6 (67%) were macrolide susceptible, 7 (78%) were up to date with vaccinations. The median number of contacts identified per case was 8 (range 1- 30) with 1 case from a correctional facility having 30 contacts; 3 (33%) cases were lost to follow up. No cases were identified through contact tracing.
Conclusions and Future Actions
We attribute the increase in cutaneous diphtheria notifications to be most likely due to the increased toxin testing of C. diphtheriae isolates. Contact tracing activities in the NT are challenging and resource intensive due to high population mobility. Improved understanding of carriage and transmission and the development of a diphtheria SoNG (Series of National Guidelines) is recommended, as is maintaining high rates of vaccination coverage.