What Is Diphtheria? Symptoms, Spread & Why Australia Is Seeing Cases Again

There are diseases most of us assume are no longer a real concern in Australia. Diphtheria is one of them. Decades of routine childhood vaccination pushed it to the margins, and it has been uncommon here for so long that many people have never seen a case.

So when health authorities began reporting a sharp rise in diphtheria notifications in early 2026 up till today, it caught attention.

Australia is now in the middle of its largest recorded diphtheria outbreak. The cases have been concentrated in remote and outer regional areas, and Aboriginal and Torres Strait Islander communities have been disproportionately affected. 

Diphtheria is a bacterial infection that can affect the throat, airways or skin. In serious cases, it can interfere with breathing and damage the heart and nervous system. The good news is that it is preventable, treatable, and well understood by public health teams. 

In this article, we explain what diphtheria is, how it spreads, the symptoms to look out for, and why some communities are being more affected than others.

What is diphtheria?

Diphtheria is a bacterial infection that can affect the throat, airways or skin. It is caused by toxin-producing bacteria, most commonly Corynebacterium diphtheriae, and sometimes Corynebacterium ulcerans. The toxin is what makes diphtheria potentially serious, because it can damage tissue and, in more severe cases, affect the heart, nerves and breathing.

There are two main ways diphtheria may appear: respiratory diphtheria and cutaneous diphtheria, which means skin diphtheria.

Respiratory diphtheria

Respiratory diphtheria affects areas such as the nose, throat and airways. It may start with symptoms that feel similar to other infections, such as a sore throat, fever or swollen neck glands. However, in more serious cases, a thick greyish-white coating can form over the throat or tonsils. This can make breathing difficult and may require urgent medical care.

Cutaneous diphtheria

Cutaneous diphtheria affects the skin. It may appear as slow-healing sores, ulcers or infected wounds, often on the legs or arms. These skin infections may not always look dramatic at first, but they can still spread the bacteria to others if they are not treated properly. In the current Australian outbreak, the Australian Centre for Disease Control have reported a high proportion of cutaneous diphtheria cases, with about 30% of cases classified as respiratory diphtheria.

What are the symptoms of diphtheria?

The symptoms of diphtheria can look different depending on where the infection develops. Some people may have symptoms that seem mild at first, while others can become seriously unwell. This is why diphtheria can sometimes be difficult to recognise early.
We’ve established before that there are two main types to be aware of: respiratory diphtheria and cutaneous diphtheria, also known as skin diphtheria.

Respiratory diphtheria symptoms

Respiratory diphtheria affects the nose, throat and airways. It may start like a common throat infection or cold, which can make it easy to overlook in the early stages.

Symptoms may include:

• Sore throat
• Mild fever or chills
• Swollen glands in the neck
• Difficulty swallowing
• Hoarse voice
• Tiredness or generally feeling unwell
• Nasal discharge

In more serious cases, a thick greyish-white coating, or membrane, can form at the back of the throat, nose or tonsils. This can make it hard to breathe or swallow and may become life-threatening if not treated quickly. The Australian Centre for Disease Control notes that the toxin produced by the bacteria can also lead to serious complications such as inflammation of the heart or paralysis.

Skin diphtheria symptoms

Cutaneous diphtheria affects the skin. It may begin when bacteria enter through a cut, bite, scratch or existing wound.

Symptoms may include:

• Slow-healing sores or ulcers
• Infected wounds that do not improve as expected
• Sores often appearing on the legs or arms
• A grey, moist-looking scab or coating over the wound
• Redness, swelling or discomfort around the affected area

Skin diphtheria is often less severe than respiratory diphtheria, but it is still important. The bacteria can spread from infected wounds to other people through close contact or shared items, especially if the wound is not covered or treated.

Because symptoms can vary, anyone with a persistent sore throat, breathing difficulty, or slow-healing skin sores should seek medical advice. This is especially important for people living in, working in, or travelling through areas where diphtheria cases have been reported.

How does diphtheria spread?

Diphtheria spreads through close contact with an infected person. How it spreads can depend on whether the infection is in the throat and airways, or on the skin.

Respiratory diphtheria can spread when an infected person coughs or sneezes, releasing tiny droplets into the air. Another person may become infected if they breathe in those droplets, especially during close contact. It can also spread through direct contact with saliva or respiratory secretions.

Cutaneous diphtheria, can spread through direct contact with infected sores, ulcers or wounds. This may happen through skin-to-skin contact, or through contaminated items such as towels, bandages, clothing, bedding or utensils.

Why is Australia seeing diphtheria cases again?

There is no single confirmed reason why Australia is seeing more diphtheria cases again. Public health authorities are still monitoring the outbreak and investigating how it is spreading. However, experts believe several factors may be contributing at the same time.

Lower vaccination coverage in some communities

One of the main suspected factors is lower vaccination coverage in some communities. This may include people who missed childhood vaccinations, people who have not received a booster for many years, or people who have had difficulty accessing vaccination services.

Diphtheria is vaccine-preventable, and vaccination provides strong protection against the severe effects of the diphtheria toxin. However, if vaccination rates fall in a community, there may be more opportunity for the bacteria to spread and cause illness.

Diphtheria has been rare for many years

Another reason diphtheria can reappear is that it has been uncommon in Australia for a long time. Because many people have never seen a case before, symptoms may not be recognised straight away.

This is especially true for skin diphtheria, which may look like a slow-healing sore, ulcer or infected wound rather than a serious bacterial infection. If cases are not identified early, the bacteria may continue to spread through close contact before treatment begins.

Remote location and healthcare access

The current outbreak has mostly affected people in outer regional and remote areas, particularly in the Northern Territory and Western Australia. In these areas, distance from healthcare services can make it harder to access vaccination, early diagnosis and treatment quickly.

This is not about where someone comes from or their background. It is more about the practical barriers that can affect health access, such as long travel distances, fewer local services and delays in getting medical care.

Misinformation and vaccine hesitancy

Health experts have also raised concerns that misinformation and vaccine hesitancy may affect some people’s decisions around vaccination. This does not entirely mean everyone who is under-vaccinated is anti-vaccine. In many cases, people may have missed doses because of access issues, lack of awareness, cost concerns, language barriers, or not knowing when boosters are due.

Clear, trusted and culturally appropriate health information is important so people can make informed decisions and access vaccination when needed.

For reliable updates, you can visit:

• Australian CDC Diphtheria resource collection — for fact sheets, brochures and community health resources.
• Australian Immunisation Handbook — for official vaccine and booster recommendations.
• National Centre for Immunisation Research and Surveillance — for vaccine research, immunisation updates and outbreak commentary.
• State and territory health departments — especially for people living in or travelling to higher-risk areas, as local advice may change quickly.

How can diphtheria be prevented? 

 Diphtheria is a vaccine-preventable disease, which means vaccination is the most important way to reduce the risk of serious illness. Good hygiene, wound care and early medical advice can also help reduce spread, especially during an outbreak.

Keep vaccinations up to date

Vaccination helps protect against the severe effects of diphtheria toxin, which is what can make the infection dangerous. In Australia, diphtheria vaccination is included in routine childhood immunisation schedules, and booster doses may be recommended at different stages of life. The Australian Immunisation Handbook recommends diphtheria-toxoid vaccine as part of the childhood schedule at 2, 4, 6 and 18 months, and again at 4 years of age.

Adults may also need boosters, especially if they are unsure when they last had a diphtheria-containing vaccine. People living in or travelling to higher-risk areas are advised to check their vaccination status and speak with a healthcare professional. The Australian CDC says people travelling to higher-risk areas should consider vaccination if they have not had a diphtheria vaccine in the past 5 years.

Wear a mask when respiratory symptoms are present

Because respiratory diphtheria can spread through droplets from coughing and sneezing, wearing a mask may help reduce the spread of respiratory droplets when someone is unwell or in close-contact settings.

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Seek medical advice early

Early diagnosis and treatment can help reduce the risk of complications and prevent further spread. Anyone with symptoms such as a persistent sore throat, breathing difficulty, swollen neck glands, or slow-healing skin sores should seek medical advice, especially if they live in or have recently travelled to a higher-risk area.

It is best to call ahead before visiting a clinic or hospital if diphtheria is a concern, so staff can give the right advice and take precautions if needed.

Take care of cuts, sores and wounds

Because skin diphtheria can spread through infected sores or ulcers, good wound care is important. Clean cuts, bites and scratches properly, keep wounds covered, and avoid sharing towels, bandages, clothing or bedding if someone has an infected sore.

Slow-healing wounds, ulcers or skin infections should be checked by a healthcare professional rather than left untreated.

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Practise good hygiene

Simple hygiene steps can also help reduce the spread of many infections, including diphtheria. This includes washing hands regularly, covering coughs and sneezes, disposing of used tissues, and avoiding close contact with others when unwell.

For skin infections, it is also important to avoid touching sores and then touching other people or shared items.

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Clean and disinfect shared surfaces

Diphtheria can spread through close contact with respiratory secretions, infected wounds, and sometimes contaminated personal or household items. Regular cleaning of high-touch surfaces and shared items using suitable cleaners and disinfectants may help reduce contact transmission, especially in homes, clinics, schools, care settings or shared living environments.

Follow public health advice

During an outbreak, public health teams may provide specific advice for affected communities. This may include testing, antibiotics, vaccination clinics, contact tracing or advice for close contacts.

The Australian CDC says current public health responses include identifying and treating cases, testing close contacts, offering vaccination and antibiotics when indicated, and educating people about symptoms and prevention.