A diphtheria outbreak has swept through the Northern Territory, infecting 131 people and likely claiming one life. Researchers say overcrowded homes and poor skin health are fuelling the spread.

This marks the first return of locally transmitted, toxin-producing diphtheria to the Territory in over twenty years.

Researchers recorded 97 skin infections and 34 respiratory cases between January 2025 and April 2026, according to a study in Eurosurveillance.

Aboriginal people made up 95 per cent of those infected—125 out of 131 cases.

"Because of high vaccination rates, the Northern Territory of Australia had not seen locally transmitted toxigenic Corynebacterium diphtheriae since the 1990s," the researchers wrote.

They described the ongoing outbreak as being "characterised by a high proportion of cutaneous cases with transmission driven by crowding and consequent poor skin health".

Thirty-nine people needed hospital care, including 12 with respiratory diphtheria. Two ended up in intensive care.

One adult, fully vaccinated as a child but without a recent booster, likely died from myocarditis linked to the outbreak.

Diphtheria is a bacterial disease, preventable by vaccine, that attacks the throat or infects skin wounds.

The researchers said most cases had been relatively mild, likely because of previous vaccination.

"Despite high vaccination rates, diphtheria has re-emerged in the NT," they wrote.

"Disease has been predominantly mild."

Of the 12 people hospitalised or killed by respiratory diphtheria, two had never been vaccinated. Seven others had not received a diphtheria shot in over a decade.

By February 2026, 95.4 per cent of Aboriginal and Torres Strait Islander children in the NT were fully vaccinated against diphtheria by age five.

The study found Aboriginal people bore the brunt of the outbreak, a result of entrenched social and health inequalities—crowded, substandard housing and high homelessness rates among them.

"Diphtheria is well known to take hold in marginalised populations," the researchers wrote.

High rates of scabies, skin sores and other infections had already set the stage for skin diseases to spread, the researchers said.

"It is no surprise that introduction of a toxin-positive C. diphtheriae strain in the NT has resulted in rapid spread," they wrote.

NT Health sounded the alarm in March, rolling out antibiotics, contact tracing and booster shots in response.

The researchers said Aboriginal community-controlled health organisations would be crucial to controlling the outbreak.

They concluded that while vaccination and antibiotics remained essential, "improvements to housing must be prioritised".