Health Minister Mark Butler has raised alarms over “the largest diphtheria outbreak we’ve encountered in several decades,” as the infection, which is typically bacterial and severe, spreads across the Northern Territory and adjacent regions.
Australia largely considers diphtheria a rarity thanks to the vaccination initiatives that began in the 1930s, effectively reducing its prevalence. The disease can lead to either skin-related (cutaneous) or respiratory conditions.
Before the onset of the Covid-19 pandemic, most diphtheria cases in Australia were traced back to international sources. The Australian Centre for Disease Control notes that a significant number of these were cutaneous in nature.
Since 2020, however, small clusters of diphtheria have emerged in various parts of northern Australia, encompassing both cutaneous and respiratory infections.
The current outbreak, which started in March, predominantly affects Indigenous communities.
According to the latest figures from the National Notifiable Disease Surveillance System, the Northern Territory has reported 133 cases tied to this outbreak. Additionally, there are 79 cases in Western Australia, six in South Australia, and up to five in Queensland, with a combination of both cutaneous and respiratory cases.
It’s the first large outbreak to be seen in Australia in more than 20 years.
Butler said: “We’re 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. So we’re working very closely with the NT government, but also with the Aboriginal-controlled sector.”
The spread is being driven in part by falling vaccination rates since the Covid-19 pandemic, combined with people missing booster shots as adults.
Routine childhood immunisation coverage fell to its lowest level in five years in 2025, with the Australian immunisation handbook recommending the diphtheria vaccine for infants, children and adolescents, and routine booster vaccination in adults.
Boosters are particularly important for special risk groups such as pregnant women.
Diphtheria bacteria can live in the mouth, nose, or throat, or on skin lesions of those infected. It is spread through respiratory droplets during coughing or sneezing, or through close contact with skin lesions.
Symptoms of respiratory diphtheria include a sore throat, fever, a grey covering over the tonsils, and enlarged lymph nodes. Left untreated, respiratory diphtheria can be life-threatening.
Meanwhile, symptoms of cutaneous diphtheria include chronic, non-healing sores or shallow ulcers which can become covered by a grey membrane.
Prior to vaccination, diphtheria was a leading cause of childhood death globally. Respiratory diphtheria is significantly more deadly, killing up to one in 10 infected people even with treatment.
Both are treated with antibiotics, ideally administered promptly to limit transmission. Respiratory diphtheria may also require treatment with an antitoxin, but this needs to be administered early.
There has been one death suspected to be caused by the current outbreak, but Butler said the Northern Territory government is still investigating the cause.
“We’re waiting to see the advice of that investigation,” he said.
It would mark the first diphtheria death in Australia since 2018.
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 said quickly providing easy access to vaccinations in affected areas, including booster shots, was critical to addressing the outbreak.
Childhood immunisation coverage rates Australia-wide have decreased below the 95% aspirational target, with coverage rates for two-year-olds at about 90%, far below the target required to achieve herd immunity for highly infectious diseases.
However, 94.33% of Aboriginal and Torres Strait Islander five-year-olds are covered.
Dr Milena Dalton, the head of immunisation and health strengthening at the Burnet Institute, said the outbreak “highlights how quickly vaccine-preventable diseases can re-emerge when there are immunity gaps”.
“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,” she said.
