Experts are warning Australia's diphtheria outbreak — which has spread across state borders from a cluster in the Northern Territory to Western Australia, Queensland and South Australia — exposes serious cracks in the country's public health system
Diphtheria was first described in ancient Greece and formally named in the 1800s.
In the 1930s, diphtheria was among the top-ten causes of child death, causing more than 4,000 deaths in Australia between 1926 and 1935.
Cases fell significantly following the introduction of vaccines in the 1940s. The disease is now considered rare in Australia.
NT Health is awaiting results from an autopsy report on a possible diphtheria-related death in the Northern Territory. If confirmed, it would be the first fatal case of the infectious disease in Australia since 2018.
Federal Health Minister Mark Butler told ABC Radio National on Tuesday he was "very concerned" about the outbreak and said it was Australia's worst in decades.
He said he had met with Aboriginal medical services in Alice Springs, where "almost all of the cases" were affecting Indigenous Australians. Staff there are "deeply concerned", Butler said.
"We're working with the NT government and the Aboriginal-controlled sector to get more vaccines there," he said.
What is diphtheria?
Diphtheria is a potentially deadly infection caused by by certain strains of Corynebacterium bacteria.
The highly contagious microorganisms infect the skin and upper respiratory tract, and can produce diphtheria toxin.
Diphtheria has two presentations.
Respiratory diphtheria causes severe, painful swelling of the throat and neck that can block the passage of air and cause breathing problems.
In cutaneous or skin infection cases, the bacteria can cause ulcers and local swelling.
The bacterial toxin can also damage the heart, kidneys and brain.
Respiratory diphtheria is the more severe of the two presentations, and is potentially fatal, especially when it infects infants. No respiratory cases were recorded in children in Australia between 1992 and 2022.
What are diphtheria symptoms?
Associate professor Erin Price, a microbiology researcher at the University of the Sunshine Coast, said early symptoms include a mild fever, sore throat, and swollen neck glands for respiratory diphtheria, or skin sores with local swelling and tissue damage in cutaneous cases.
Diphtheria can cause a thick membrane to form in the throat.
"Symptoms can worsen as the bacterium blocks the airways, and the toxin can spread via blood, causing heart failure and paralysis," Price said.
How does it spread?
Diphtheria bacteria can live in the nose, mouth or on infected skin lesions, and is spread through respiratory droplets, for example, from coughing or sneezing, or by touching infected lesions.
But experts warn the current outbreak wasn't occurring "by chance".
Professor Adrian Esterman is a Professor of Biostatistics and Epidemiology in the School of Public Health at Adelaide University.
He said most cases in the current outbreak were skin infections spread through close physical contact which can be expected in overcrowded housing.
"Skin infection cases are typically less severe, but the bacteria they carry can spread to unvaccinated contacts," he said.
"Diphtheria does not return to a population by chance. It returns where vaccination coverage has slipped and where living conditions allow it to spread."
Nationally, childhood vaccination coverage at 24 months fell below 90 per cent in 2024 for the first time since 2016.
"That weakens community protection across Australia, not just in Aboriginal communities," Esterman said.
"This outbreak should not be framed solely as an Aboriginal health issue. It is also a warning about gaps in vaccination coverage, overcrowded housing, and infectious disease surveillance that have been building nationally for years."
Many of the cases in the current outbreak have occurred in remote communities.
The Australian Centre for Disease Control (ACDC) says that diphtheria notifications have been increasing in Australia since late 2025.
There have been 145 cases of diphtheria reported in the Northern Territory since the start of the year and another 75 cases in Western Australia, with most of those recorded in the Kimberley.
Why are diphtheria cases on the rise?
Professor Raina MacIntyre is head of the biosecurity program at the University of New South Wales' Kirby Institute. She said it was concerning to see a resurgence of a disease considered rare before 2020.
"This outbreak is largely locally acquired cases, mostly in Aboriginal communities, in contrast to the pre-2020 epidemiology, when it was mainly a rare, travel-imported disease.
"Diphtheria in Australia started to increase in October 2025, with another big jump in February this year, with more cases in 2026 to date than any single year in the past quarter century. This is an unprecedented epidemic, with most of it diphtheria skin infection, and about a quarter being respiratory diphtheria."
According to Price, treatment can include intravenous diphtheria antitoxin administration. Less severe cases can be treated with penicillin, macrolide, or tetracycline antibiotics.
MacIntyre said that the vaccine's efficacy does wane, so boosters are needed. Data released by the ACDC shows that almost 80 per cent of respiratory diphtheria cases had at least three doses of vaccine, while just over 53 per cent with skin diphtheria had been vaccinated.
"The occurrence of diphtheria in vaccinated people may reflect partial vaccination, missed booster doses, or weakened immunity in fully vaccinated people," MacIntyre said.
"The role of vaccine hesitancy, misinformation and trust needs to be explored."
MacIntyre said that what were once record-high levels of childhood vaccination prior to the COVID-19 pandemic in Australia, the vaccination rate had been declining in Australia since 2020.
The combined diphtheria, whooping cough and tetanus shot is free in Australia, but vaccination rates may be lower in remote communities.
"In fact, all vaccination rates have been falling, not just in Australia [but] globally," MacIntyre said.
"This is likely due to the rise in vaccine misinformation and pushback against vaccines after the COVID-19 pandemic.
"Historically, large diphtheria epidemics can occur when vaccination programs get disrupted — when the Soviet Union fell in 1991, over 140,000 cases and over 5,000 deaths resulted, in what was the largest epidemic since routine infant vaccination was the norm," MacIntyre said.
"We urgently need tools to monitor and detect health misinformation that can help us intervene early with health promotion to improve vaccine confidence."
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