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Diphtheria is one of those diseases most of us haven’t heard of.
It’s so rare in Australia that many doctors haven’t seen a case outside a textbook.
Which is where we like diseases to stay – filed alongside smallpox and iron lungs under ‘things we beat’.
So what is causing its resurgence?
The Forgotten Disease
Diphtheria is an infectious, toxin-driven bacterial disease.
The bacterium that causes diphtheria (Corynebacterium diphtheriae or C. ulcerans) is unremarkable. The real damage comes from the toxin it releases. The bacterium is the courier, delivering a toxic parcel you didn’t order.
The first and most deadly form (C. diphtheriae) sets up shop in the nose and throat. For a few days, you might assume it was just a bad cold – fever, sore throat, general misery.
But within days, the toxin can produce a thick grey membrane across the throat. It can cause swelling in the neck, difficulty swallowing and eventually block the airway completely. Left untreated, it can creep into the heart and nervous system.
The second form (C. ulcerans) infects the skin and causes large, slow-healing ulcers.
The development of a vaccine in the 1930s made diphtheria something we didn’t have to worry about. And eventually … we stopped.
Forgotten But Not Gone
Diphtheria was a common cause of death in Australian children before vaccinations became routine. In contrast, it caused two deaths in unvaccinated adults here in the 20 years prior to the COVID-19 pandemic.
Credit: Shutterstock
With 442 cases reported this year, Australia is experiencing its largest diphtheria outbreak since national records began in 1991.
The outbreaks are concentrated in Aboriginal communities across the Northern Territory, Western Australia, South Australia and Queensland.
Diphtheria spreads as you would expect – coughing, close contact, infected wounds or surfaces – and it spreads faster in areas where healthcare is harder to access and homes are crowded.
This isn’t a mysterious outbreak. It’s a predictable one.
Lessons For The Future
The response – expanded vaccine access, treatment and local outreach – is already working, with the number of new cases falling.
This is exactly what vaccines are supposed to do: work so well you forget why you needed them.
That’s the paradox at the heart of public health. Success looks like nothing happening. And nothing happening, for long enough, makes it easy to forget why it was necessary in the first place.
While our attention shifts to newer threats, old ones can continue to lurk in the background.
Infectious diseases don’t take turns – they take opportunities. Diphtheria’s return isn’t evidence that vaccines failed. It’s a reminder of what they were quietly doing all along.
