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Diphtheria outbreak update

Australia is currently experiencing the biggest diphtheria outbreak since records began. Public health authorities in impacted states and territories, primarily the Northern Territory, Western Australia and South Australia, are working hard to manage and contain the outbreak.

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Current status

Diphtheria notifications in Australia have been increasing since October 2025, with a marked increase since February 2026.

Diphtheria is caused by toxin-producing Corynebacterium diphtheriae or, sometimes, Corynebacterium ulcerans bacteria. 

The type of symptoms depend on where the infection happens in the body – either the respiratory tract or the skin. 

Cutaneous (skin) diphtheria symptoms include skin ulcers with a bluish appearance, often on the legs or arms, and infection of pre-existing skin lesions. Cutaneous diphtheria infections need wound management as they are slow healing and can become chronic if left untreated. These types of infections rarely cause the serious complications seen in respiratory diphtheria.

Respiratory diphtheria symptoms can include fever and sore throat.  A greyish-white membrane can form over the throat and tonsils to obstruct the airway causing difficulty breathing. The toxin made by the bacteria can cause myocarditis (inflammation of the heart) and paralysis. Without proper treatment, this can be fatal.

This year, there have been 230 cases of diphtheria notified in Australia, representing an approximately 30‑fold increase compared with the same period from 2022 to 2025. 

The most up to date numbers on diphtheria cases are reported through the National Notifiable Diseases Surveillance System, and our weekly epidemiology reports.

Cases are mostly from the Northern Territory and Western Australia, with additional cases reported in Queensland and South Australia.

The outbreak is characterised by a high proportion of cutaneous diphtheria, with about 30% of cases classified as respiratory diphtheria. 

Overall, most cases are considered to have had relatively mild disease, likely reflecting the protective effect of prior vaccination. 

Vaccination provides strong protection against the severe effects of diphtheria toxin, although it does not consistently prevent carriage or transmission.

The majority of cases have been among Aboriginal and Torres Strait Islander people and in outer regional and remote areas of the Northern Territory and Western Australia.  

Since records began in 1991, most years recorded somewhere between zero and 12 cases per year. The years with the highest number of cases previously were 2022, with 31 cases, and 2025, with 26 cases. 

Higher-risk areas

Areas considered higher risk for diphtheria currently include: 

  • any location in the Northern Territory  
  • the Kimberley, Goldfields and Pilbara regions in Western Australia  
  • the far northwest of South Australia.  

Public health response

The impacted states and territories are taking action to manage the outbreak responses in their jurisdictions.  

This includes: 

  • quickly identifying and treating people with diphtheria 
  • identifying, vaccinating, and testing close contacts – and giving preventive antibiotics, if these are indicated 
  • educating people with diphtheria and their contacts about the disease and steps they can take to minimise the risk of transmission 
  • promoting vaccination and making it easier to access.  

We support the response through national guidance, surveillance, and reporting. 

To help guide the states and territories in their outbreak responses, the Australian CDC in collaboration with the Communicable Diseases Network Australia urgently developed national guidance on diphtheria outbreak management.    

We monitor and report on diphtheria cases through the National Notifiable Diseases Surveillance System, to help us understand trends in diphtheria activity, impact and severity.  

 All of this information combined is critical in supporting public health units in the affected jurisdictions make important decisions on what action to take.

But it takes time for public health measures to reduce the intensity and impact of the outbreak in affected communities.  

Prevention

Vaccination is the best way to protect against illness and severe complications from diphtheria. 

We do know that most cases are mild, due to previous vaccination. However, people who are vaccinated can still carry and transmit the disease if infected. People who are unvaccinated, or whose last vaccine dose was greater than 10 years ago are at greatest risk of becoming severely unwell with diphtheria. 

For those living in or travelling to higher-risk areas, it is recommended that you consider a booster every 5 years. 

Learn more

Learn more about diphtheria webpage and see our weekly epidemiology reports.  

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