Diphtheria outbreak response for health professionals

Background

Diphtheria is a serious infectious notifiable disease caused by certain strains of Corynebacterium bacteria.

It can cause respiratory or cutaneous (skin) infections. The bacteria produce a toxin that can cause life-threatening complications including:

  • upper airway obstruction
  • heart damage
  • kidney damage
  • brain and nerve damage

Diphtheria spreads through:

  • respiratory droplets (coughing or sneezing)
  • direct contact with skin lesions

An outbreak of diphtheria was reported from the Northern Territory and Western Australia at the end of 2025, with cases increasing significantly in early 2026. A small number of cases of diphtheria associated with this outbreak were notified in South Australia in April 2026. The outbreak is predominately impacting Aboriginal people.

Vaccines to protect against diphtheria have been safely used in our immunisation programs to protect young children, teenagers and pregnant women against diphtheria for many years.

For general information on diphtheria see Diphtheria - including symptoms, treatment and prevention.

A public health diphtheria outbreak response has been implemented to keep people safe and to limit and prevent further cases of diphtheria in SA.

The outbreak response includes:

Clinical presentation

There are two main forms of diphtheria: respiratory and cutaneous. Milder illness is more common in persons who are vaccinated.

Respiratory diphtheria

Respiratory diphtheria primarily affects the tonsils, pharynx, nose and larynx. In severe cases it causes a pseudomembrane at the back of the throat presenting a risk for airway obstruction.

Symptoms and signs of respiratory diphtheria may include:

  • Fever
  • Sore throat
  • Malaise
  • Enlarged tender cervical lymph nodes
  • Difficulty swallowing
  • Discharge from the nose

Signs of severe respiratory diphtheria include:

  • Clinical evidence of pseudomembrane in inadequately vaccinated person
  • Bull neck / progressive lymphadenopathy
  • Stridor
  • Signs of sepsis (delayed capillary refill, cold extremities or tachycardia)
  • Respiratory distress such as chest in-drawing or central cyanosis.

Cutaneous diphtheria

Cutaneous diphtheria causes a non-healing ulcer or sore.

Symptoms and signs of cutaneous diphtheria may include:

  • Chronic non-healing ulcer which may be
    • Painful or mildly tender
    • Have a punched out appearance
    • Have purulent discharge or slough
    • Have a grey or white membrane covering the base
  • Skin sore which may have surrounding redness and crusting and be difficult to distinguish from impetigo

Diphtheria can cause cardiac (cardiomyopathy, myocarditis), neurological (peripheral neuropathy and cranial neuropathies) and kidney complications.

 The case fatality rate for untreated, never vaccinated cases of diphtheria is approximately 30% and between 5-10% for classic respiratory diphtheria, even with appropriate treatment.

Mode of transmission

Transmission occurs person to person via respiratory droplets or direct contact with respiratory secretions or cutaneous exudate of an infected person. It is also spread from indirect contact with items contaminated with nose, throat or wound discharges.

Incubation period

Usually 2 to 5 days (range 1-10 days)

Infectious period

The period of communicability is variable. It remains infectious while bacterial shedding occurs. However, persons who are asymptomatic carriers are generally considered less infectious.

The infectious period likely starts for respiratory cases 7 days prior to symptom onset and for cutaneous cases the date of skin infection.

Without treatment persons with diphtheria can remain infectious for weeks to several months.

Respiratory diphtheria is considered infectious until demonstration of two negative throat swabs.

Cutaneous diphtheria is considered infectious until at least 72 hours of appropriate antibiotics and the wound can be covered.

Diagnosis

Preliminary diagnosis is usually made based on clinical presentation. Where diphtheria is suspected it is imperative to begin presumptive therapy quickly before confirmatory test results are available.

Diphtheria is diagnosed by testing (for PCR and culture) appropriate clinical specimens. Suitable samples include oropharyngeal or throat swabs, nasal and nasopharyngeal swabs, skin ulcer swabs, pseudomembrane tissue, sputum and sterile site samples. Ideally two samples should be collected from each suspected case. Where possible samples should be taken before antibiotics are commenced.

Infection control

For patients with suspected or confirmed diphtheria the following measures should be taken:

  • For suspected or confirmed respiratory diphtheria use standard, contact and droplet precautions. Recommended PPE includes gown, gloves, eye protection and surgical mask. Wear a PFR if performing aerosol generating procedures (e.g. intubation).
  • For suspected or confirmed cutaneous diphtheria where respiratory diphtheria has been excluded, use standard and contact precautions. Recommended PPE includes at a minimum gown and gloves, and where there is risk of blood or body fluid exposure, also wear a mask and eye protection, such as when irrigating wounds. Wear a PFR if performing aerosol generating procedures.

For further details see:

Treatment

Diphtheria is treated with antibiotics. Severe cases require hospitalisation and diphtheria antitoxin. For further details see: Interim Management of Diphtheria in Clinical Settings in South Australia (PDF 390KB).

Contacts of persons with diphtheria should be managed as per the:

Isolation and exclusion period

  • Exclude cases of respiratory diphtheria from work, school and childcare until completion of appropriate antibiotics and clearance testing returns a negative result. Where possible, cases should have two nasopharyngeal and/or throat swabs at least 24 hours after completion of the antibiotic course, and at least 24 hours apart.
  • Exclude cases of cutaneous diphtheria from work, school and childcare until wounds are healing or clinically improving, can be covered with an occlusive waterproof dressing, have completed recommended vaccination and at least 72 hours of appropriate antibiotics.

Prevention

Exclude persons with diphtheria as per isolation and exclusion period.

Vaccination recommended against diphtheria. For more information see Diphtheria Outbreak Response Immunisation Program.

Notification

The Communicable Disease Control Branch, South Australia, should be notified on suspicion of diphtheria on 1300 232 272 (24 hours/7 days) to enable prompt public health follow up.