Australia is in the midst of its worst diphtheria outbreak in over three decades, with more than 230 cases since the start of the year, increasing markedly since February – underscoring the need to ensure patients’ vaccinations are up to date, experts say.

Most cases have occurred in the Northern Territory (133), followed by Western Australia (79), while six have been reported in South Australia and three in Queensland, with the vast majority being in remote and very remote areas (82%) and about 15% in outer regional areas, according to the latest data released by the Australian Centre for Disease Control last week.

According to the Australian CDC, the entire Northern Territory, the Kimberley, Goldfields and Pilbara regions in Western Australia and the far northwest of South Australia are currently considered higher risk for diphtheria.

Last week the government announced $7.2 million in funding to help the NT government and Aboriginal Community Controlled Health services respond to the outbreak.

The majority of cases (94%) have been in Aboriginal and Torres Strait Islander people, and while the cause of the outbreak is not yet known, socioeconomic factors and crowding likely play a role, says Dr Archana Koirala, a paediatrician, infectious disease specialist and clinical researcher at the University of Sydney.

Up-to-date vaccination is key

Notably, around 90% of cases in this outbreak have occurred in people who have already had at least one dose of the vaccine – with 45% of people who contracted diphtheria having had five doses.

“They’re not an unvaccinated cohort, and because of that, the disease seems to be on the mild side, albeit there has been one person who has died with diphtheria,” Dr Koirala says.

Ensuring patients are up-to-date with their immunisation is crucial, she says.

Nationally, the diphtheria combination vaccine (dTpa) is funded under the NIP for children at 2 months, 4 months, 6 months, 18 months, 4 years, and 12 to 13 years, as well as for pregnant women.

The Australian Immunisation Handbook also recommends boosters for other adults, including travellers to countries where health services are difficult to access (every 10 years) and to places where the risk of diphtheria is higher (every five years). The full recommendations are explained in the AIH here.

New guidance in the NT

In the Northern Territory, an additional dTpa dose is now recommended for Aboriginal and Torres Strait Islander people and frontline workers in remote communities if it has been more than 5 years since their previous dose. That includes teachers, police, healthcare, child care and aged care workers, paramedics and correctional facility staff.

Additional doses are also funded in the NT for other adults not in those groups if it has been more than 10 years since their last dose – as well as for people with a mild case of diphtheria or who have been in close contact with someone who has diphtheria.

Be vigilant

Dr Koirala says it’s also important monitor the outbreak, “because it has spread to an extent where we didn’t anticipate. Even in areas where you might think that you don’t have an outbreak, be vigilant.”

“If someone comes in with a diphtheria-like illness or has travelled to an outbreak setting, then keep that differential in your mind.”

“Make sure that your cohort is immunised and up-to-date, and report everything that they’re given into AIR, even if it’s not NIP funded,” she adds.