What is melioidosis and why do cases spike after flooding and heavy rainfall?

The Guardian

05-03-2025

After major floods in north Queensland at the start of this year, 119 cases of the bacterial disease melioidosis were reported – more than three times the number of cases reported in the same period in 2024.
Of these cases, 106 were from the areas around Cairns and Townsville. Sixteen people have died so far.
So what is the potentially fatal disease, why are we seeing a spike in cases and what could it mean for people in the aftermath of Tropical Cyclone Alfred?
Melioidosis is a rare but potentially fatal bacterial disease which occurs when people have significant contact with contaminated water or soil.
Associate Professor Jeffrey Warner, a microbiology researcher from the Australian Institute of Tropical Health and Medicine at James Cook University, describes melioidosis as an 'opportunistic infection' preying on people with pre-existing health conditions such as diabetes and kidney problems as well as those who take immune-suppressing medicines. Heavy consumers of alcohol are more at risk, while people in good health are generally not susceptible to serious illness.
Warner says melioidosis is a 'great mimicker' of other infections, commonly presenting as a severe chest infection with symptoms of cough, fevers and chills. But it can also affect the skin and internal organs.
This mimicry can be dangerous, Warner warns, as the disease is very aggressive and resistant to most antibiotics used to treat standard infections. So rapid identification of melioidosis is critical to ensure correct 'top shelf' antimicrobial treatment. If untreated, pneumonia and sepsis can develop.
Melioidosis can be fatal in up to 20% of treated cases, but Warner says people often die with the organism (from complications such as renal failure) not from it.
Melioidosis is caused by the bacterial species Burkholderia pseudomallei which are found in the soil and water of tropical regions and considered endemic in Queensland and the Northern Territory. The bacteria is usually located deep in the soil but can be freed by environmental disruption, particularly floods and rainfall. It is most likely to occur in muddy soils. Infection can then occur when the bacterial cells enter susceptible people's bodies through cuts, sores, breathing it in or drinking dirty water.
According to a spokesperson for Queensland Health, there have been 119 cases including 16 deaths due to melioidosis in 2025, as of 5 March.
Warner says the number of cases in such a brief period is unprecedented but not surprising, because extreme weather is known to cause more cases. Given the number of cases, the rate of fatalities is within the expected rate of 5-10%, he says. 'Even when people present in well resourced hospitals, the disease can be fatal.'
Because many older Australians come to Queensland to retire, they often have a higher prevalence of comorbidities, such as diabetes, that are associated with increased incidence of disease and fatality rates, he says.
The disease is spread through environmental exposure – it does not usually spread between people or animals.
The bacterial species is spread through the environment by rainfall, runoff water or potentially winds. 'Humans can influence its moving around by disrupting the environment … its growing health burden is at the intersection of changing climate, environment and land use,' Warner says.
The bacteria typically prefers soils in the tropics, but there is evidence when climate and environmental change moves the bacteria to a non-tropical environment, it can persist, Warner says.
Warner says Tropical Cyclone Alfred, expected to hit Queensland's south-east coast, could bring a spike in a number of infections associated with floods and rainfall generally, but the vast majority won't be melioidosis.
Since 2013, cases of melioidosis outside north Queensland have only been in the single digits, Warner says. In 2024 there were 10 cases for whole year in the south of the state, so there is a 'little bit of evidence that meliodosis may be on the uptick but it's nowhere near as significant as up in the north'.
People affected by the cyclone in the state's south-east could be more significantly affected by mosquito-borne infections, skin lesions caused by other fungi and bacteria in the environment or gastro if sewerage systems don't work, he says.
However, it is possible the bacteria which causes melioidosis could travel through aerosolisation. People could potentially breathe it in when particles are carried in the air due to rains and winds during cyclonic events, he says.
A spokesperson for Queensland Health encouraged Queenslanders to take precautions including wearing waterproof boots and protective gloves during cleanup following flooding events and always avoid contact with flood water if they have any broken skin or wounds.