NORTHERN TERRITORY — A study published in the journal Eurosurveillance investigated a diphtheria outbreak in Australia's Northern Territory between 2025 and 2026. This outbreak resulted in 131 identified cases and one adult death.

The cases occurred from January 2025 to April 2026. The outbreak was recognized as the first documented recurrence of locally acquired diphtheria in the Northern Territory in over 20 years. Aboriginal Australians accounted for 125 of the reported cases, and the outbreak was ongoing as of April 30, 2026.

The cases included 97 cutaneous cases, which involved skin lesions, and 34 respiratory cases. Cutaneous cases began to emerge in May 2025, while respiratory cases appeared in March 2026. While respiratory infections were more commonly found in Central Australia, cutaneous infections largely affected the Top End region.

Among respiratory patients, 12 required hospitalization, and 2 were admitted to intensive care. The deceased adult had completed a childhood vaccination series but had not received a booster dose within the preceding 10 years. The majority of patients with severe respiratory infections either had no prior vaccination or had a gap of more than 10 years since their last diphtheria-containing vaccine.

Testing was conducted on 76 isolates, which were all found to be susceptible to erythromycin and to penicillin with increased exposure. No major antimicrobial resistance genes were identified in these tested isolates. The dominant outbreak strain belonged to sequence type 381, with phylogenetic analysis estimating that this strain shared a common ancestor dating to approximately 2017. All 19 sequenced isolates carried the tox gene allele type 20, and five isolates produced toxin as confirmed by the Elek immunoprecipitation assay at an overseas public health laboratory.

Researchers observed that vaccination appeared to decrease the severity of the disease, though it did not completely prevent infection or its spread. Overcrowded housing and poor skin health were identified as environmental and social factors associated with transmission of diphtheria within the affected communities.