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Melioidosis – and its Wet Season connection
Dr Ella Meumann from Menzies School of Health Research discusses melioidosis, a predominantly wet season disease caused by the soil-dwelling bacterium Burkholderia pseudomallei. Ella works with Professor Bart Currie on the Darwin Prospective Melioidosis Study, which has tracked all culture-confirmed cases of melioidosis in the Top End since 1989. She acknowledges the role of her colleagues, including Dr Kay Hodgetts, who was involved with research into the Katherine region.
Hi Ella, thanks for joining us. What melioidosis symptoms should nurses be looking for?
Melioidosis has wide-ranging clinical manifestations. Pneumonia is the most common presentation, and symptoms may include fever, shortness of breath, cough, purulent sputum production, and pleuritic chest pain.
Many patients have bloodstream infection, and may have sepsis or septic shock.
Any organ system in the body can be involved. Prostatic abscess is common in men, presenting with fever and urinary retention. B. pseudomallei can cause abscesses in the liver or spleen, and bone and joint infections. Encephalomyelitis is a rare but potentially devastating presentation.
Some cases have a chronic presentation, with cough, weight loss, and a cavitary lung lesion mimicking tuberculosis. Others have a chronic non-healing skin ulcer. Such patients may be systemically well.
Melioidosis should be considered a possible diagnosis in cases of patients with sepsis, particularly during the wet season, and particularly in patients with risk factors.
Which risk factors exactly?
Through the Darwin Prospective Melioidosis Study (DPMS), we’ve identified some key risk factors, including diabetes, hazardous alcohol consumption, chronic kidney disease, and immunosuppression, for example cancer chemotherapy.
From the research, it emerged that nine patients contracted melioidosis because of Katherine River flooding in January 1998. Of the nine, five recalled an inoculating injury. Patient history seems highly relevant as well?
We think most cases are acquired either by percutaneous inoculation through skin trauma, or by inhalation of aerosolised bacteria during severe weather events. It’s not uncommon for melioidosis patients to recall a particular event, such as an injury sustained while gardening, or being caught in a severe storm.
Some people may have occupational exposures through their work outdoors. Others may undertake recreational activities that increase their exposure. Most people exposed to B. pseudomallei do not get melioidosis – it is those with comorbidities affecting the immune system who are most at risk.
What sort of incubation period are we dealing with?
Based on the time between inoculating injury and symptom onset for patients in the DPMS, the incubation period is between one to 21 days.
How is melioidosis diagnosed?
Diagnosis requires culture of B. pseudomallei from clinical specimens. We recommend collecting blood cultures, ideally two sets from different sites at different times, throat and rectal swabs in Ashdown’s medium if that’s available, and other specimens depending on the site of infection; for example, sputum, urine, skin swabs, and pus specimens. If melioidosis is suspected or there are particular environmental exposures, please document this on the pathology request form as it will inform specimen processing in the laboratory.
Melioidosis is understood to be associated with severe weather events. What role will climate change play in the spread of melioidosis?
In the Top End, the vast majority of cases occur during the wet season from November to April.
Spikes in cases, as seen in the Katherine study, can occur following severe weather events such as cyclones, high rainfall, and high winds.
It is predicted that as the climate changes there will be an increase in the frequency and severity of extreme weather events such as cyclones, and it is likely that melioidosis cases will increase in association those changes.
Is there also a chance it will head further south, as weather patterns shift?
Yes. The regions of its endemicity are predicted to expand further south in Australia.
How far south has it been found up until now?
There have been occasional cases reported in Central Australia and in Southeast Queensland, in association with periods of heavy rainfall.
What sort of health promotion messages should remote clinics focus on?
Health promotion should target those at greatest risk of becoming unwell with melioidosis – individuals with diabetes, hazardous alcohol consumption, chronic kidney disease, or other immunosuppression.
During the wet season it is recommended that people wear shoes, and gloves while gardening. People with risk factors should stay indoors during storms. This advice could be incorporated into a health check, for example.
Cultural considerations and social disadvantage may mean it is less likely for protective footwear to be worn in some remote areas. There’s clearly some complexity here?
More work needs to be done to understand the most effective ways of preventing melioidosis. It is likely that barriers exist to enacting the preventive measures described above. Some people may have housing insecurity, which may mean sleeping rough and increased B. pseudomallei exposure – addressing high homelessness rates in remote northern Australia is vital. Treatment and prevention of diabetes, chronic kidney disease, and hazardous alcohol consumption are also very important. All of this requires adequate funding and community partnerships.
What does treatment look like, and what’s the role of the remote area nurse in all of this?
Treatment includes an intensive phase of at least two weeks of intravenous antibiotics, and an eradication phase of at least three months of oral antibiotics. The duration of each phase depends on the severity of the infection and the body site that is involved, with treatment decisions made in consultation with the infectious diseases team.
Nursing staff play a key role. Remote area nurses recognise sepsis, collect appropriate specimens for culture, and start management with fluids and empiric sepsis antibiotics (as outlined in the CARPA Standard Treatment Manual) – all of that can be life-saving.
Likewise once a patient returns to a community, remote area nurses play an important role in supporting that person through the eradication phase of treatment so that they don’t have relapse of infection.
Hospital-based nurses also play an extremely important role. In the Emergency Department, the Intensive Care Unit, and on the wards, they provide expert management of sepsis. The Hospital In The Home nurses play a key role in supporting completion of intravenous treatment.
How important is fast treatment?
It can take 48 hours for B. pseudomallei to be isolated from clinical specimens and for the diagnosis of melioidosis to be made. If someone is critically unwell, there may not be time to wait for that information. The recommended antibiotics outlined in Top End sepsis guidelines including the CARPA Standard Treatment Manual have activity against B. pseudomallei.
Any takeaway messages for our readers?
I’d just like to thank all the nurses involved with the care of melioidosis patients in the Top End – you do a wonderful job!
Want to learn more about wet-weather diseases? Read the second part of our December wet-weather disease feature on Japanese encephalitis virus.