Overview
Diphtheria is a rare but serious infectious disease caused mainly by toxin-producing strains of Corynebacterium diphtheriae and, less often, Corynebacterium ulcerans. It can infect the throat and nose or the skin. The most serious illness happens when the bacteria produce diphtheria toxin, which can damage the heart and nerves.
Outbreak update as of June 2026: Australia is experiencing its largest diphtheria outbreak in decades. As at 1 June 2026, 288 cases had been notified in 2026, mainly in the Northern Territory and Western Australia, with smaller numbers in South Australia and Queensland. About two-thirds of cases have been cutaneous disease and about one-third are respiratory diphtheria. Most cases have occurred in Aboriginal and Torres Strait Islander people and in rural and remote communities.
For Aotearoa New Zealand, the overall risk of importation is considered low, but diphtheria should be considered in returning travellers with severe throat illness or non-healing skin ulcers.
Immunisation remains the best protection against diphtheria. Ensuring people are up to date with the National Immunisation Schedule, including booster doses where appropriate, provides the strongest protection against disease.
We will continue to monitor the situation closely and provide updated advice to the sector if the risk assessment or recommendations change.
Introduction
While some diphtheria cases may be mild, the bacteria can produce dangerous toxins that cause severe complications - which can be life-threatening. Complications include heart trouble, paralysis, and kidney failure. Cases of diphtheria in New Zealand have declined significantly over the last century with very few cases reported in the last 50 years.
Although diphtheria is now uncommon in New Zealand, it has resurged in several parts of the world since 2020, including large outbreaks in West Africa, a major multi-country outbreak in Europe in 2022, and ongoing transmission in Australia in 2025-2026. This means New Zealand cases are still most likely to be linked to travel or close contact with someone exposed overseas.
Transmission
Diphtheria is spread by close personal contact with someone who is infected or is a carrier of the bacteria and shows no symptoms. Spread commonly occurs via respiratory droplets, originating from a cough or a sneeze. The bacteria can also spread through contaminated objects or food.
Traditional tattooing has also been implicated in cases of skin infection in New Zealand.
People can carry the bacteria without feeling unwell, and skin infection can help the bacteria spread to others. Vaccination provides excellent protection against the harmful effects of diphtheria toxin, but it does not always prevent a person from carrying the bacteria or transmitting it to others.
As milder disease can still result in vaccinated people, diphtheria should remain a consideration in individuals presenting with compatible symptoms following travel to outbreak areas or countries where diphtheria is endemic.
Symptoms
Symptoms usually start 2-5 days after exposure.
Respiratory diphtheria causes inflammation of the upper respiratory tract, including the nose and throat. Symptoms may include sore throat, breathing problems, bloody or watery drainage from the nose, hoarseness, a bark-like cough and painful swallowing. Swelling of the throat and neck is characterised by a ‘bull neck’.
Cutaneous diphtheria is a skin infection that usually presents as chronic, non-healing sores or shallow ulcers, sometimes covered by a grey membrane. The diphtheria toxin can cause serious complications affecting the heart, nerves, and kidneys.
Prompt assessment and management are required if diphtheria is suspected. However, some cases may not experience any symptoms.
Treatment
People suspected of having diphtheria will be given an antitoxin injection. Antitoxin works best when given early because it only neutralises toxin that has not yet bound to tissues. Infection is then treated with antibiotics, such as benzathine penicillin or erythromycin. Reduced susceptibility to some commonly used antibiotics has been reported in recent outbreak strains, and laboratory testing and specialist advice may be needed to guide antibiotic treatment.
Cutaneous diphtheria also needs wound care because skin lesions can stay infectious and heal slowly. Additional treatment may include intravenous fluids, oxygen, bed rest, heart monitoring, use of a breathing tube, and correction of any blocked airways.
A person with diphtheria and their close contacts will be managed by public health services. This may include isolation, testing, preventive antibiotics for contacts, and catch-up or booster vaccination. People who recover from diphtheria should still be vaccinated because infection does not reliably provide long-term protection.
Risks
Respiratory diphtheria can still be fatal even with treatment. Recent evidence shows that full vaccination greatly lowers the risk of severe disease and death, but unvaccinated or under-vaccinated people remain at highest risk, especially young children. Cutaneous disease is often less toxic, but it remains important as it can sustain transmission and lead to respiratory cases.
The effects of diphtheria can range from mild to severe.
- For those infected, there is the potential for the diphtheria bacteria to release harmful toxins which can spread through the blood stream and affect major organs
- Diphtheria toxin can cause significant damage to the heart, nerves, and kidneys
- Diphtheria can be fatal - 5-10% of those infected die, even with treatment.
Prevention
Vaccination is the best protection against diphtheria. Long-term protection requires a full primary course followed by booster doses across the life course.
If you are travelling to an outbreak setting, make sure you are up to date with diphtheria containing vaccines.
