Diphtheria a Communicable Disease Incident of National Significance – 26 May 2026

26 May 2026: Australia’s Chief Medical Officer has declared diphtheria a Communicable Disease Incident of National Significance (CDINS). This assists enhanced coordination of national and jurisdictional control efforts. Diphtheria notifications in Australia have been increasing since October 2025, with a marked increase since February 2026.

In 2026 there have been more than 230 cases, with the majority in the Northern Territory and Western Australia. This is an approximately 30‑fold increase compared with the same period from 2022 to 2025. Most cases have been among Aboriginal and Torres Strait Islander people. Cases have mainly been in very remote, remote and in outer regional areas.

Seven cases of diphtheria have been notified in South Australia (SA).

Diphtheria is caused by toxin-producing  Corynebacterium diphtheriae or, rarely other diphtheria-toxin producing Corynebacterium species. The incubation period is usually 2 to 5 days (range 1-10 days). It is spread from human to human via respiratory droplets or contact with skin lesions, or indirect contact, and causes respiratory or cutaneous infections. There can be cardiac, neurological or renal complications. The case fatality rate for respiratory diphtheria is 5-10%. Vaccination provides strong protection against the severe effects of diphtheria toxin, but diphtheria can occur in persons who are age appropriately vaccinated and vaccination does not consistently prevent carriage or spread.

Diphtheria – including symptoms, treatment and prevention

Diphtheria is an infection of the throat and nose caused by a toxin produced by the bacterium Corynebacterium diphtheriae.

Diphtheria has been rare in Australia since the introduction of an effective vaccine, but a century ago, was the most common infectious cause of death. Outbreaks still occur in countries where vaccination rates are not high.

Diphtheria is a notifiable condition¹

How diphtheria is spread

People can carry the diphtheria bacterium harmlessly in the nose and throat (‘carriers’). The diphtheria bacterium is spread when an infected person (patient or carrier) talks, coughs or sneezes small droplets containing infectious agents into the air. The droplets in the air may be breathed in by those nearby. The diphtheria bacterium is also spread by indirect contact with hands, tissues or other articles soiled by nose and throat discharges, or by indirect contact with skin sores.

Signs and symptoms of diphtheria

Symptoms include:

• sore throat
• swollen neck glands
• discharge from the nose.

The bacteria can also produce a toxin capable of damaging nerves or the heart.

Occasionally these bacteria can cause skin infections, usually in people with poor health or poor hygiene.

Diagnosis of diphtheria

Diphtheria is suspected when a white or grey membrane is seen on the back of the throat and is confirmed when the bacteria are seen under the microscope and grown in the laboratory.

Incubation period

(time between becoming infected and developing symptoms)
Usually 2 to 5 days.

Infectious period

(time during which an infected person can infect others)

Without antibiotic therapy, usually less than 2 weeks but occasionally as long as 6 months. A person is no longer infectious after treatment with appropriate antibiotics.

Treatment of diphtheria

Specific treatment with antibiotics and an antidote to the toxin is available.

Prevention for diphtheria

• People with diphtheria need to be kept in isolation until they are certified to be free of the disease by SA Health’s Communicable Disease Control Branch (CDCB).
• Contacts of people with diphtheria need to be investigated for the disease, receive antibiotics and receive vaccination if required. A contact is any person who has been close enough to an infected person to be at risk of having acquired the infection from that person.
• Family or household contact with diphtheria should be excluded from childcare, preschool, school and work until cleared to return by the CDCB.
• Contacts whose work involves food handling or caring for unimmunised children are excluded from work until they certified to be free of the disease by the CDCB.
• Widespread immunisation against diphtheria is the only effective control. The diphtheria vaccine is administered through the National Immunisation Program. The first dose of diphtheria vaccine, in combination with other vaccines, is now recommended to be given at 6 weeks of age. For adolescents and adults, the combined diphtheria, tetanus, pertussis vaccine is preferred, if not given previously, as it provides additional protection against whooping cough (pertussis).
• People travelling to countries where diphtheria is common should have received a full course of immunisation and consider a booster dose of vaccine in discussion with their doctor.

Diphtheria Outbreak Response Immunisation Program

The state-funded Diphtheria Outbreak Response Immunisation Program (the Program) has been introduced in response to an increase in diphtheria cases in Aboriginal communities.

Vaccination against diphtheria is most effective at preventing severe disease. Vaccines to protect against diphtheria have been around and safely used in our immunisation programs to protect young children, teenagers and pregnant women against diphtheria for many years.

Diphtheria vaccine program priority areas

• Anangu Pitjantjatjara Yankunytjatjara (APY) Lands
• Oak Valley
• Yalata
• Ceduna (and surrounds)
• Oodnadatta
• Coober Pedy

Free funded diphtheria-containing vaccines are available for the following priority groups:

High and medium risk contacts¹ of a confirmed diphtheria case who have not had a diphtheria-containing vaccination in the past 12 months.

• Low risk contacts¹ who have not had a diphtheria-containing vaccination in the past 5 years.
• Aboriginal people 10 years and older residing in SA who have not had a diphtheria-containing vaccination in the past 5 years

¹Contacts as identified in the SA Health – Diphtheria Contact Management Table.

Children, adolescents and women who are pregnant living in priority outbreak areas should be age appropriately vaccinated as per the National Immunisation Program.

https://www.sahealth.sa.gov.au/wps/wcm/connect/public+content/sa+health+internet/conditions/immunisation/immunisation+programs/diphtheria+immunisation+program