What is it?

Diphtheria is a rare but potentially life-threatening acute illness caused by the bacteria Corynebacterium diphtheriae. This bacteria can produce a potent toxin which causes serious disease. It mostly commonly causes an acute respiratory illness characterised by a “pseudo membrane” which forms over the pharyngeal area (throat).

Other less common forms of illness caused by C. diphtheriae include laryngeal/tracheobronchial diphtheria, nasal diphtheria and cutaneous diphtheria.

What to look for

The incubation period is 2-5 days. Early symptoms include low-grade fever, lethargy and malaise. Affected people may develop a sore throat, which may cause pain on swallowing or a hoarse voice.

One to two days after symptom onset, a “pseudo membrane” develops in 95% of cases, which appears as a thick, grey and leathery membrane at the back of the throat. This is formed from cell debris and inflammatory exudate. Breathing difficulty may occur, especially if part of the membrane dislodges and obstructs the airway.

Toxin-related complications include myocarditis (heart muscle inflammation), neuropathy (nerve damage) and in rare cases, acute tubular nephropathy (kidney damage).

How is it transmitted?

Diphtheria is very contagious and is spread by inhalation of respiratory droplets from an infected person. Diphtheria can also be spread via skin lesions, in cases of cutaneous diphtheria, and the bacteria can also survive on environmental surfaces for weeks.  Asymptomatic carriers may transmit the bacteria.

Humans are the only known reservoir for diphtheria.

Epidemiology

In the pre-vaccine era, young children (< 10 years old) were at highest risk for contracting diphtheria.  Diphtheria previously represented one of the leading causes of death in childhood, with an associated mortality rate of 5-10%.

Diphtheria is now rare in high income countries with high vaccination coverage, but remains endemic in many lower income countries. Outbreaks across the globe continue to be an issue, with 16,000 cases worldwide reported in 2018.

Cases in Australia are more commonly associated with the return of international travellers.

Prevention

Diphtheria is vaccine-preventable, with protection available through administration of combination vaccines routinely administered via the National Immunisation Program (NIP) at:

  • 6 weeks, 4 months and 6 months – Infanrix hexa
  • 18 months – Infanrix/Tripacel
  • 4years – Infanrix IPV/Quadracel
  • 12-13 years (Year 7) – Boostrix

Additional doses of Boostrix are recommended and funded for pregnant women during every pregnancy (regardless of how closely spaced). Further doses are recommended (not funded) for adults at ≥ 50 years of age, if their last dose was more than 10 years ago. Regular boosters are recommended every 10 years for travellers to high risk countries, and for some high-risk laboratory workers.

Injection site pain is commonly reported following diphtheria vaccination. This is usually mild and resolves within a few days. Uncommon side effects reported include headache, lethargy, malaise and fever.

Resources

Authors: Julia Smith (RCH Immunisation Fellow) and Rachael McGuire (MVEC Education Nurse Coordinator)

Date: April 2022

Materials in this section are updated as new information and vaccines become available. The Melbourne Vaccine Education Centre (MVEC) staff regularly reviews materials for accuracy.

You should not consider the information in this site to be specific, professional medical advice for your personal health or for your family’s personal health. For medical concerns, including decisions about vaccinations, medications and other treatments, you should always consult a healthcare professional.