Diphtheria returns to the Northern Territory
The NT Centre for Disease Control is investigating a diphtheria outbreak in the Northern Territory. Four cases of respiratory diphtheria have been notified since 23 March 2026 - two in Darwin and two in Alice Springs - alongside 37 cases of cutaneous (skin) diphtheria notified since May 2025. A public health alert was issued on 31 March 2026.
This outbreak is quite unusual. Respiratory diphtheria has not been seen in the Territory for over 26 years. The skin form is more common, but the recent cluster of respiratory cases has prompted heightened vigilance from clinicians and public health authorities.
While a diphtheria outbreak might be very unusual in Australia, it isn't unusual when considering infectious disease globally. Between 12,000 and 24,000 cases are reported to WHO on an annual basis.
In 2023/24, more than 28,000 cases and 828 deaths were reported across Nigeria, Guinea, Mauritania, and South Africa, with more than 80% of cases coming from Nigeria. According to the report on the outbreak, only 24% of cases were fully vaccinated, with 70% under the age of 15 years.
Outbreaks of vaccine preventable disease are often a reflection of the impact of vaccine shortages, armed conflict, and poverty on vaccination programs.
What is diphtheria?
Diphtheria is caused by a bacterium, Corynebacterium diphtheriae. The bacteria produce a toxin which can have life threatening effects on the upper airway. It is also responsible for serious systemic effects on the body. These include myocarditis, and kidney damage. Humans are the only reservoir of the disease and transmission can occur through respiratory droplet infection or via direct contact with the skin. It can also be transmitted by raw milk.
Diphtheria was a common cause of death in children prior to the 1950's. It is now very rare, largely due to our very successful national immunisation program (NIP). For more background on why this disease has faded from public consciousness in Australia, see our earlier article: Diphtheria; the forgotten disease.
Cases of diphtheria are more likely to enter Australia from overseas and this is where secondary prevention is necessary. Contacts of a case are monitored for illness and swabs are taken from the upper airway. A vaccine booster is given if they are not up to date. Health Departments have the right to pursue contacts of cases.
Diphtheria is a notifiable disease in Australia.
Signs and symptoms
Respiratory diphtheria can present with a sore throat, mild fever, and loss of appetite. In more severe cases, a thick grey membrane can form across the back of the throat, and swelling of the lymph nodes and surrounding tissue can produce a characteristic "bull-neck" appearance. Untreated, respiratory diphtheria can be life-threatening and breathing may become difficult.
Cutaneous (skin) diphtheria typically presents as chronic, slow-healing sores or shallow ulcers, often on the legs, which may also become covered by a grey membrane.
The bacteria spread through respiratory droplets from coughing or sneezing, and through direct contact with skin sores.
How is it prevented?
Primary prevention is by vaccination. Diphtheria is a component of the Infanrix hexa, or Vaxelis vaccine. It is given in the first year of life. A child is born with the mother's immunity and this wanes over time. Doses of the vaccine are given at 2, 4 and 6 months with a booster of a diphtheria containing vaccine at 4 years. This provides the child with their own immunity.
In the NT, the diphtheria vaccine is free through the National Immunisation Program for children at 6 weeks, 2, 4, 6 and 18 months, and again at 4 and 12 years. Adults are recommended to have a booster every 10 years, and pregnant women are recommended a single dose of dTpa between 20 and 32 weeks of each pregnancy to provide protection to newborns.
It is also a component of the triple antigen (diphtheria/tetanus/pertussis, dTpa). This is often given after an injury (for the tetanus component) or in the 3rd trimester of pregnancy (for the whooping cough component). These "other doses" help to keep the community herd immunity high, locking out potential transmission.
Individuals are often reminded to review their routine immunisations when travelling. A common one is tetanus. It is fortunate that diphtheria, tetanus and whooping cough can all be updated in one vaccine (Adacel, Boostrix). If you are planning a trip overseas, you can book a virtual travel health consultation to review your vaccination history with one of our travel doctors.
Diphtheria is also available in combination with tetanus, whooping cough and polio (Adacel polio, Boostrix IPV) and might be considered for travellers to regions where vaccine associated polio is being reported (as of 30 March 2026). Wild polio is currently only being reported in Pakistan and Afghanistan.
