One of Australia's worst diphtheria outbreaks has officially claimed its first fatality after tests confirmed the disease was the probable cause.
However, authorities say the rate of cases has dramatically dropped in the Northern Territory at the centre of the outbreak following a vaccination blitz.
NT Health on Tuesday confirmed a man's death in April was diphtheria-related after autopsy results from an overseas laboratory were returned.
"The final toxicology tests have come back demonstrating that the diphtheria bug is producing a toxin that can cause these health effects," NT Chief Health Officer Paul Burgess said.
"We now say that is probable as the cause of death for that individual."
He also dismissed reports that a second man had died from the disease on Sunday.
"I would like to be very clear that that sad death that happened in Alice Springs Hospital was not associated with diphtheria," he said.
The NT has the bulk of the nation's 248 reported cases to date, with 163 currently in the territory - 48 of them being the potentially deadly respiratory infection.
The remainder are in Western Australia, South Australia and Queensland.
However NT Health Minister Steve Edgington said the territory's rate had declined following a $7.2 million federal funding package to combat the disease and improve vaccination rates.
"We have seen a reduction in the number of reported cases and while we're not out of the woods it is important to recognise that that reduction has continued," he said.
Dr Burgess said the rate had roughly halved from up to 22 cases a week at its peak to only nine in the past seven days, with more than 10,000 residents immunised.
Health authorities have been working in partnership with Aboriginal health agencies to get people vaccinated in remote communities where the virus has spread.
"We've done a mountain of work in terms of improving our vaccination rates," Dr Burgess said.
"In the last seven weeks alone, more than 10,000 vaccines are in arms protecting Territorians against diphtheria.
"Our aim is by the end of this year to have vaccine rates as high as we can to really terminate this outbreak."
The NT had very high vaccination rates in Aboriginal communities of above 90 per cent but that had dropped to 89 per cent, he said.
When hundreds of cases were first reported last week, Federal Health Minister Mark Butler said the outbreak was about 30 times greater than the average number of diphtheria cases nationally over the past five years.
Compared to the current 248 cases, there were 26 reported in 2025 and only nine in 2024.
Dr Burgess said it was likely the current diphtheria strain was imported from overseas into northern Queensland in 2022 as its "genetic fingerprint" was evident in the NT outbreak.
