Health Minister Mark Butler has expressed concern about what he calls "the biggest diphtheria outbreak we've seen, certainly for decades," as the serious bacterial infection spreads through the Northern Territory and into Queensland, South Australia, and Western Australia. Diphtheria, which can cause either skin (cutaneous) or respiratory disease, has been considered rare in Australia since a vaccination rollout began in the 1930s - a fact that makes this outbreak feel like an unwelcome trip in a time machine.
Prior to the Covid-19 pandemic, most Australian cases were imported from overseas, and a high proportion were cutaneous diphtheria. But since 2020, small clusters have appeared in northern Australia, involving both types. The current outbreak began in late 2025, with the Northern Territory Centre for Disease Control declaring an outbreak in March. It is affecting Indigenous people almost exclusively. Latest data from the National Notifiable Disease Surveillance System shows 133 cases in the Northern Territory, 79 in Western Australia, six in South Australia, and up to five in Queensland - a mix of cutaneous and respiratory cases. It's the first large outbreak in Australia in more than 20 years.
Butler said the government is working with the NT government and the Aboriginal-controlled sector to get more vaccines there. "There's no question this is serious," he told ABC Radio National on Tuesday. "It's serious in the NT. It's spreading across other parts of the Top End. It's crept below the South Australian border into the APY Lands." The spread is driven in part by falling vaccination rates since the pandemic, combined with people missing booster shots as adults. Routine childhood immunisation coverage fell to its lowest level in five years in 2025, despite the Australian immunisation handbook recommending the diphtheria vaccine for infants, children, adolescents, and routine booster vaccination in adults - with boosters particularly important for pregnant women.
Diphtheria bacteria can live in the mouth, nose, throat, or on skin lesions, and spread through respiratory droplets or close contact with lesions. Symptoms of respiratory diphtheria include a sore throat, fever, a grey covering over the tonsils, and enlarged lymph nodes; left untreated, it can be life-threatening. Cutaneous diphtheria features chronic, non-healing sores or shallow ulcers that can become covered by a grey membrane. Dr John Boffa, public health medical officer at the Central Australian Aboriginal Health Congress in Alice Springs, said one third of cases in the outbreak are respiratory diphtheria. "Skin diphtheria can lead to respiratory diphtheria in other people, and so it's all concerning, and we're seeing about 20 new diphtheria cases a week," he said. "That hasn't slowed down yet, and of the new cases, about a third are being hospitalised, and that's significant, because the Northern Territory hospital system operates on the edges all the time."
Before vaccination, diphtheria was a leading cause of childhood death globally. Respiratory diphtheria kills up to one in 10 infected people even with treatment. Both types are treated with antibiotics; respiratory cases may also require an antitoxin administered early. There has been one death suspected to be caused by the current outbreak, but Butler said the NT government is still investigating. If confirmed, it would be the first diphtheria death in Australia since 2018. "It's 95% certain that this unfortunate person died because of diphtheria," Butler said. "It's very clear that this person had diphtheria on the skin and inside of his respiratory system and developed a well-known complication of diphtheria, which is inflammation of the heart."
Prof Robert Booy, an infectious diseases paediatrician, said diphtheria was "readily transmitted in close quarters of families especially," making spread more likely in overcrowded housing. He stressed the need for quick access to vaccinations and booster shots. Childhood immunisation coverage rates Australia-wide have fallen below the 95% aspirational target, with coverage for two-year-olds at about 90% - far below the level needed for herd immunity. However, 94.33% of Aboriginal and Torres Strait Islander five-year-olds are covered. Boffa said vaccination efforts are gathering pace: "The initial issue was just access to the vaccine. I think we've got on top of that, we've got enough vaccine. There's pop-up clinics that are just starting this week. But this outbreak has happened on the background of an ongoing workforce problem with nurses and GPs, and so the capacity to vaccinate at scale is not there yet."
Dr Milena Dalton, head of immunisation and health strengthening at the Burnet Institute, summed it up: "Diphtheria remains rare in Australia because vaccination works. But this outbreak is a reminder that rare does not mean impossible, and that protection needs to be maintained through timely boosters for adolescents and adults." In other words, a disease we thought we'd left in the history books has found a loophole.