2026 — More Than 17 Times the Previous Peak of 31 Cases in 2022. the Cases Have Been Reported Primarily in the Northern Territory

The federal government says it is delivering a $13 million package to support affected jurisdictions responding to the outbreak. The latest report from the Australian Centre for Disease Control (CDC) notes cases peaked between late May and early June this year and have since declined across affected jurisdictions. The CDC told the ABC that in the last fortnight 26 cases were reported, compared to almost 80 at the height of the outbreak.

However, public health experts warn a drop in testing means actual numbers could be higher. Megan Campbell, a public health physician and medical adviser at the National Aboriginal Community Controlled Health Organisation (NACCHO), said while the lower case numbers were encouraging, testing rates had not been consistently high across affected areas. "We're just a little bit cautious about how we interpret that data when we're hearing that testing is quite low in some parts of Australia, Dr Campbell said.

"So we do worry with that drop in numbers that part of that may be due to a lack of testing in some areas. Diphtheria is a highly contagious and dangerous bacterial infection that can affect the nose, throat, airways or the skin. It is treated with antibiotics, and vaccination is considered the primary line of defence.

The disease spreads through respiratory droplets from coughing or sneezing, or direct contact with infected wounds. Most cases this year have spread through skin lesions, with the vast majority among Aboriginal and Torres Strait Islander people in outer regional and remote areas. Professor of epidemiology at Adelaide University, Adrian Esterman, said while the type of diphtheria which mainly affected the skin was generally milder, that could mean it sometimes went undetected or could be mistaken for something else.

"Unfortunately Aboriginal children and adults are prone to skin lesions, especially in crowded housing." He said if people had scabies or insect bites, that could increase the risk of diphtheria spreading. Dr Campbell urged people in affected regions to remain vigilant and proactive in being tested. "We still really want people to be coming in early for testing if they've got skin infections or skin sores or a sore throat," she said.

"Serious illness can occur from diphtheria and the hospitalisation rate for this outbreak has been around 20 per cent … we really do want people to keep thinking about diphtheria and keep talking to their health professionals and coming in to get their vaccination. Once a leading cause of childhood deaths and historically known as the "strangling angel", diphtheria has been considered largely eliminated in Australia since the 1950s, on the back of routine vaccination use. Governments and public health experts have attributed this outbreak to a complex cluster of factors, such as waning immunity and housing conditions.

The CDC report said a high proportion of people with diphtheria in 2026 had received at least three valid vaccine doses. However, CDC epidemiologist Stephanie Williams said vaccine immunity wanes over time, and urged people to stay up to date with vaccines and boosters." "Whilst those antibody levels generally do decline over time, they are still providing some protection [and] when we look at the cases in this outbreak, we have seen mostly mild disease, Dr Williams said. Experts note the outbreak has disproportionately affected people in lower socio-economic areas, where poor housing conditions and crowding have meant the disease has spread easily." "What I'm talking about is overcrowded housing, housing that's not been designed or maintained for large families and where there's inadequate health hardware in the home, Dr Campbell said. "So that's making sure there's enough space, enough beds and bedding, enough towels, consistent water, soap and so on so that people can maintain a healthy living situation.