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Diphtheria

Current outbreak – May 2026

Australia is currently experiencing the largest diphtheria outbreak on record, with cases increasing since October 2025 and rising sharply from February 2026. (1) The majority of cases have been identified in the Northern Territory and Western Australia, with additional cases in Queensland and South Australia. (1) To date, 230 cases of diphtheria have been notified in Australia, representing a substantial increase compared with 2022, when 31 cases were reported. (1)

The Australian Centre for Disease Control has characterised this outbreak as having a high proportion of cutaneous diphtheria, with approximately 30% of cases classified as respiratory diphtheria. (1)

What is it? 

Diphtheria is a communicable disease caused by the Corynebacterium diphtheriae and  Corynebacterium ulcerans bacteria, which can cause serious respiratory and skin infections. (2, 3) Prior to accessible and widespread vaccination for diphtheria, an estimated 1 million cases of diphtheria and 50,000 – 60,000 deaths occurred annually in low and middle-income countries. (4) Following the expanded and accessible diphtheria vaccination programs, reported cases decreased by over 90%. (4)

Symptoms of respiratory diphtheria include a fever, severe sore throat, malaise, runny nose, and a grey or black membrane coating on the tonsils and throat caused by bacterial-produced toxins, which can lead to breathing and swallowing problems(5). Symptoms of cutaneous diphtheria include skin ulcers and wounds that are sore, full of pus and may be surrounded by greyish skin patches(5).

How is it transmitted? 

Diphtheria is spread through the infectious respiratory particles of a carrier or infected person, via direct deposition of particles on the exposed facial mucosa of a person, or through contact transmission of a contaminated surface. (6)

Symptoms of diphtheria can occur between 2-5 days after infection, and can last for four to six weeks in people who are untreated. (3, 5)

Transmission terminology

The use of the term ‘infectious respiratory particles’, rather than ‘droplet’, is used to more accurately recognise the differences in respiratory particle sizes and transmission routes (7, 8). This is in line with ACIPC’s Policy Statement, Terminology for pathogens that transmit through the air (7).

At risk groups 

Diphtheria is usually considered to be of low incidence in Australia, New Zealand and other high-income countries due to high rates of childhood vaccination(5, 8), however, it still exists in many settings where vaccines are not available or vaccination rates are low.

People at risk of diphtheria include those who are unvaccinated, those who have not received booster vaccinations, and travellers to or from areas with known diphtheria cases and outbreaks, including South East Asia, and Eastern Europe. (2, 5)

Prevention 

Vaccination is the best way to prevent diphtheria infection. Diphtheria vaccination should be administered to children in a multi-dose schedule, as a booster to adolescents, and as a booster dose every ten years for adults(8, 9).

Cases of diphtheria should be managed with preventative measures that include strict hand hygiene, respiratory etiquette, and the use of PPE consistent with standard and transmission-based precautions when in a healthcare facility. Regular cleaning with a detergent and disinfectant of contaminated and high-touch surfaces will prevent contact transmission.

Key messages: 

  • Diphtheria is a vaccine preventable disease, with booster vaccinations needed to maintain immunity.  
  • Vaccination is free through the National Immunisation Program for children and pregnant women.  

References 

  1. Australian Center for Disease Control. Diptheria outbreak update Canberra: Australian Center for Disease Control,; 2026 [Available from: https://www.cdc.gov.au/newsroom/news-and-articles/diphtheria-outbreak-update.
  2. Centres for Disease Control and Prevention (CDC). Diphtheria Atlanta: Centres for Disease Control and Prevention; 2022 [Available from: https://wwwnc.cdc.gov/travel/diseases/diphtheria.
  3. NSW Health. Diphtheria fact sheet Sydney: NSW Government; 2022 [updated 14 November 2022. Infectious diseases fact sheet]. Available from: https://www.health.nsw.gov.au/Infectious/factsheets/Pages/diphtheria.aspx.
  4. World Health Organization. Diphtheria vaccine: WHO position paper. 2017;92:417-36.
  5. Better Health Channel. Diphtheria Melbourne: Victorian Department of Health 2017 [updated 29-08-2017. Available from: https://www.betterhealth.vic.gov.au/health/healthyliving/diphtheria#symptoms-of-diphtheria.
  6. National Health and Medical Research Council (NHMRC). Australian Guidelines for the Prevention and Control of Infection in Healthcare. Canberra: National health and Medical Research Council; 2019.
  7. Australasian College for Infection Prevention and Control. Terminology for pathogens that transmit through the air. Australasian College for Infection Prevention and Control, ; 2026 February 2025.
  8. Health New Zealand Te Whatu Ora. Te rongoā āraimate mō te pakaua hukihuki, te whakapokenga korokoro me te mare tekekō (Boostrix). Tetanus, diptheria and whooping cough vaccine (Boostrix) New Zealand: Health New Zealand; 2023 [
  9. Australian Technical Advisory Group on Immunisation (ATAGI). The Australian Immunisation Handbook. Canberra: Australian Government Department of Health and Aged Care; 2022.

 

UPDATED 21 May 2026