Toxigenic diphtheria cases in North Queensland, Australia
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Torres and Cape Hospital and Health Service, Australia
Townsville Hospital and Health Service, Australia
Cairns and Hinterland Hospital and Health Service, Australia
Publication date: 2023-04-27
Popul. Med. 2023;5(Supplement):A256
Background and Objective: Diphtheria is predominantly caused by toxigenic Corynebacterium diphtheriae and presents as both respiratory and cutaneous disease. Locally acquired tox-gene-carrying diphtheria is rare in Australia and cases have all but disappeared from the country since the 1950s with widespread uptake of the diphtheria toxoid vaccine. Since 2018, there has been an increase in locally acquired cutaneous and respiratory cases of toxigenic C diphtheriae across North Queensland, Australia with whole genome sequencing of specimens identifying a genetically-linked cluster of cases in the region. Here we present the epidemiology of this outbreak. Methods: We retrospectively reviewed all notifications of confirmed Corynebacterium diphtheriae cases occurring in the North Queensland region between 2000 and 2022. Demographic, clinical and exposure source details were extracted from Queensland Health’s Notifiable Conditions System and laboratory typing results obtained from Queensland Health Forensic and Scientific Services. Data were de-identified and analysed using Microsoft Excel 2021. The Townsville Human Research and Ethics Committee approved the study. Results: There have been 29 notified cases of genetically linked tox-gene-carrying diphtheria across North Queensland since 2020, 23 of which occurred in 2022. Three cases presented with classic respiratory diphtheria, four with mild respiratory diphtheria and 22 with cutaneous diphtheria. All infections were acquired in Australia and all cases had epidemiological links to the North Queensland region. A total of 86% of cases (25/29) identified as Aboriginal and/or Torres Strait Islander people. All cases were managed with penicillin or azithromycin, vaccination, and diphtheria antitoxin (DAT) where appropriate. Household contacts were screened for symptoms, administered chemoprophylaxis, and offered a diphtheria-containing vaccination if due. Conclusions: This outbreak contributes to the broader global concerns for increasing diphtheria outbreaks. Timely vaccinations in children, adolescents, pregnant women, and eligible older people remain of upmost importance. Australian clinicians and public health professions should remain vigilant for future cases.