Melioidosis

Queensland Health Guidelines for Public Health Units

Revision History

VersionDateChanges
1.0February 2010 Full revision of guideline. 
2.0 August 2023Full revision of guideline

Infectious agent

The agent is a bacterium, Burkholderia pseudomallei (B. pseudomallei).

Case definition and notification criteria

Report only laboratory confirmed cases.

Confirmed case
A confirmed case requires laboratory definitive evidence.

Laboratory definitive evidence
Isolation of B. pseudomallei from any site.

Notification procedure

Pathology laboratories

Melioidosis is notifiable on pathological diagnosis.

Objectives of surveillance

  1. To monitor the epidemiology of melioidosis in Queensland.
  2. To identify disease clusters so that appropriate public health action can be taken.

Public health significance and occurrence

B. pseudomallei, the causative agent of melioidosis, is a gram-negative environmental bacterium widely found in soil and water of tropical and sub-tropical regions. It is an opportunistic human pathogen. B. pseudomallei is endemic to Northern Australia, the Pacific Islands, South East Asia and South Asia/Indian subcontinent. Areas of highest documented global burden of human disease include Northern Australia and Thailand1. Annual case numbers worldwide for 2015 were estimated at 165,000 with a predicted 89,000 deaths2. The true global distribution of B. pseudomallei and burden of disease is unknown or under reported due to limited laboratory capacity in some endemic regions1.

Human and environmental isolates collected from 30 countries across Australasia, Asia, Africa, Central and South America support the hypothesis that Australia was the early reservoir of bacteria with onward transmission attributed to the movement of humans and cargo. Australasian and South East Asian isolates demonstrate increased genetic diversity and specific virulence factors that may contribute to geographically distinct clinical manifestations3.

Cases notified in Queensland are often seasonal in nature (December – May) and are commonly reported in residents of the Torres and Cape, North West, Cairns and Hinterland and Townsville regions. Although there are increasing reports of cases in other parts of Queensland including South East Queensland4. Cases are predominantly seen in residents however can present in travelers.

Increased incidence of melioidosis can be observed following tropical storms and extreme weather5, 6, 7. Rise in temperature, global precipitation patterns and an increased incidence of extreme weather events are expected to change the global epidemiology of melioidosis8.

Mortality rates overall are reported from less than 10 percent in Australia up to 40 percent in Thailand. Higher case fatality rates can be associated with limited diagnosis and treatment options in low resource countries9. Increasing incidence of melioidosis in endemic areas of Australia over time has not been associated with increased mortality, likely due to improvements in sepsis recognition and access to critical care resources10, 11, 6.

Aboriginal and Torres Strait Islander peoples are disproportionately affected by melioidosis in endemic regions of Australia11, 12. The average notification rate in Aboriginal and Torres Strait Islander Queenslanders between 2012-2016 was 5.7 cases per 100,000 population per year compared to 0.4 cases per 100,000 population per year for non-Indigenous Australians4. In far north Queensland melioidosis cases among Aboriginal and Torres Strait Islander persons were of younger age and had a higher case fatality rate10.

B. pseudomallei is identified as a potential bioterrorism agent13.

Clinical features

Melioidosis is a bacterial infection which most commonly presents clinically as septicaemia and/or pneumonia. Other presentations include skin abscesses or ulcers, genitourinary infection, neurological disease, osteomyelitis or septic arthritis and deep tissue abscesses in the internal organs such as the liver, prostate or spleen4, 10, 12.

Cutaneous melioidosis often presents as a non-healing ulcer or skin abscess14.

Low incidence rates of disease are observed among children. Children are more likely than adults to present with single skin abscesses without fever or bacteremia6, however fatalities and bacteremia have been reported15. A cluster of paediatric cutaneous melioidosis has been reported in association with a mud play event in northern Queensland in 2022 (A. Preston-Thomas, personal communication, December 2022).

Chronic melioidosis (symptoms ≥ 2 months) can present with subacute pulmonary disease or non-healing skin infections, and generally has a more benign course than acute disease.

Recurrence of melioidosis is uncommon. The Darwin 30-year prospective melioidosis study reported a 5 percent recurrence rate among 1,148 primary infections6. Recurrent melioidosis, identified by culture positive disease post treatment completion, can be described as a relapse or new infection depending on epidemiological information and comparative genomic typing. Disease recurrences, sometimes years following initial presentation, can be associated with inadequate source control or duration/compliance of eradication therapy10.

Laboratory

Diagnostic gold standard is culture from specimens including blood, respiratory secretions, urine, cerebrospinal fluid (CSF) or wound swabs. Suspicion of melioidosis should be noted on the pathology request to allow for specific media if required.

Serology has limited utility in the diagnosis of acute melioidosis, particularly in endemic areas1.

PCR testing of clinical specimens for B. pseudomallei is also limited due to genetic variability and lack of validation1.

Reservoir

The organism is saprophytic and is found in certain soils and waters. Various animals including sheep, goats, horses, swine and rodents can become infected and transfer the agent to new environmental foci.

Mode of transmission

Transmission is usually via direct contact with contaminated soil or water through overt or inapparent skin wounds. Transmission is also believed to occur via inhalation/aspiration or ingestion of contaminated water droplets, soil or dust. The proportion of cases attributable to inhalation versus percutaneous is unknown and thought to be dependent on geographical location, weather patterns, occupational/recreational behaviour and host factors16.

Zoonotic transmission is not known to occur.

Incubation period

Usual incubation period ranges between 1-21 days, (mean 9 days). However, years may elapse between presumed exposure and appearance of clinical disease, although prospective studies suggest this is very uncommon17. Rapid onset within hours can occur in association with inhalation and a high infective dose18.

Period of communicability

Person to person transmission is very rare. Neonatal cases have been documented following perinatal transmission and breast feeding in association with mastitis. Laboratory-acquired infections are rare18.

Susceptibility

Disease in humans is uncommon even among people in endemic areas who have close contact with soil or water containing the infectious agent.

Clinical illness, severe disease and death following exposure to B. pseudomallei is strongly dependent on host risk factors such as diabetes, hazardous alcohol use, chronic renal disease, chronic lung disease or immunosuppression12,18. Other contributing factors include the strain of B. pseudomallei, virulence factors, route of infection and exposure dose6.

Management

Cases

Investigation

In consultation with the attending medical practitioner, ascertain possible source of infection, including recreational or occupational activities that may lead to potential exposure to contaminated soil, water or travel. This may be of particular importance for cases occurring outside known endemic areas.

Treatment

Recognition of sepsis and rapid commencement of intensive (usually intravenous) antibiotic treatment according to Therapeutic Guidelines1 and specialist advice is important. Required empiric therapy may differ from guideline recommendations in temperate regions. Specialist advice should be sought about long-term eradication therapy to prevent relapse.

Counselling

The case should be advised of the nature of the infection and its mode of transmission.

Contacts

Contact tracing

Contact tracing is not required. Consideration may be given to informing others potentially exposed to the possible source of the infection.

Community clusters

If there is any temporal and geographical clustering of cases, further steps may need to be taken urgently. These may include:

  • examining the genetic relationship of the ‘cluster’ isolates using molecular techniques
  • collecting appropriate soil and/or water samples for culture for B. pseudomallei
  • notification to local health care providers (GPs, community health centres, hospitals) about the cases/cluster, with a request to be alert for signs and symptoms of melioidosis
  • implementation of a communication strategy to inform the local community about the cases or disease cluster and to recommend measures to minimise the risk of infection.

Preventive measures in endemic areas

Health education

  • Avoid contact with soil or muddy water, particularly after heavy rains.
  • Wear footwear and use gloves for gardening or while working outdoors, especially for those with predisposing conditions.
  • Open wounds, lesions or burns should be protected from coming into contact with potentially contaminated soil or water through the use of waterproof dressings. If potential exposure occurs skin should be washed thoroughly.
  • Foot and wound care and infection prevention is important for people with diabetes.
  • Consider wearing a mask when using a high-pressure hose around soil or spraying high-pressure bore water.
  • Participants in activities involving exposure to mud in endemic areas should be cautioned about potential risk of melioidosis. A risk assessment may be required prior to undertaking these activities where large numbers of participants are anticipated.

References

  1. Gassiep I, Armstrong M, Norton R. Human Melioidosis. Clin Microbiol Rev 2020;33:e00006-19. https://doi.org/10.1128/CMR.00006-19.
  2. Limmathurotsakul D, Golding N, Dance DA, Messina JP, Pigott DM, Moyes CL, et al. Predicted global distribution of Burkholderia pseudomallei and burden of melioidosis. Nat Microbiol 2016;1:15008. https://doi.org/10.1038/nmicrobiol.2015.8.
  3. Chewapreecha C, Holden MTG, Vehkala M, Välimäki N, Yang Z, Harris SR, et al. Global and regional dissemination and evolution of Burkholderia pseudomallei. Nat Microbiol 2017;2:16263. https://doi.org/10.1038/nmicrobiol.2016.263.
  4. Communicable Diseases Branch. Melioidosis in Queensland 2012-2016 2017. https://www.health.qld.gov.au/__data/assets/pdf_file/0026/671183/melioidosis-qld-2012-2016.pdf.
  5. Chen Y-L, Yen Y-C, Yang C-Y, Lee MS, Ho C-K, Mena KD, et al. The Concentrations of Ambient Burkholderia Pseudomallei during Typhoon Season in Endemic Area of Melioidosis in Taiwan. PLOS Neglected Tropical Diseases 2014;8:e2877. https://doi.org/10.1371/journal.pntd.0002877.
  6. Currie BJ, Mayo M, Ward LM, Kaestli M, Meumann EM, Webb JR, et al. The Darwin Prospective Melioidosis Study: a 30-year prospective, observational investigation. The Lancet Infectious Diseases 2021;21:1737–46. https://doi.org/10.1016/S1473-3099(21)00022-0.
  7. Kaestli M, Grist EPM, Ward L, Hill A, Mayo M, Currie BJ. The association of melioidosis with climatic factors in Darwin, Australia: A 23-year time-series analysis. Journal of Infection 2016;72:687–97. https://doi.org/10.1016/j.jinf.2016.02.015.
  8. Merritt AJ, Inglis TJJ. The Role of Climate in the Epidemiology of Melioidosis. Curr Trop Med Rep 2017;4:185–91. https://doi.org/10.1007/s40475-017-0124-4.
  9. Currie BJ. Melioidosis and Burkholderia pseudomallei : progress in epidemiology, diagnosis, treatment and vaccination. Curr Opin Infect Dis 2022;35:517–23. https://doi.org/10.1097/QCO.0000000000000869.
  10. Stewart JD, Smith S, Binotto E, McBride WJ, Currie BJ, Hanson J. The epidemiology and clinical features of melioidosis in Far North Queensland: Implications for patient management. PLOS Neglected Tropical Diseases 2017;11:e0005411. https://doi.org/10.1371/journal.pntd.0005411.
  11. Hodgetts K, Kleinecke M, Woerle C, Kaestli M, Budd R, Webb JR, et al. Melioidosis in the remote Katherine region of northern Australia. PLOS Neglected Tropical Diseases 2022;16:e0010486. https://doi.org/10.1371/journal.pntd.0010486.
  12. Gassiep1 I, Ganeshalingam V, Chatfield MD, Harris PNA, Norton RE. The epidemiology of melioidosis in Townsville, Australia. Transactions of The Royal Society of Tropical Medicine and Hygiene 2022;116:328–35. https://doi.org/10.1093/trstmh/trab125.
  13. Melioidosis | CDC. 2022. https://www.cdc.gov/melioidosis/index.html (accessed August 4, 2023).
  14. Gibney KB, Cheng AC, Currie BJ. Cutaneous Melioidosis in the Tropical Top End of Australia: A Prospective Study and Review of the Literature. CLIN INFECT DIS 2008;47:603–9. https://doi.org/10.1086/590931.
  15. Smith S, Stewart JD, Tacon C, Archer N, Hanson J. Children with melioidosis in Far North Queensland are commonly bacteraemic and have a high case fatality rate. Commun Dis Intell Q Rep 2017;41:E318–21.
  16. Currie BJ. Melioidosis: evolving concepts in epidemiology, pathogenesis, and treatment. Semin Respir Crit Care Med 2015;36:111–25. https://doi.org/10.1055/s-0034-1398389.
  17. James GL, Delaney B, Ward L, Freeman K, Mayo M, Currie BJ. Surprisingly Low Seroprevalence of Burkholderia pseudomallei in Exposed Healthy Adults in the Darwin Region of Tropical Australia Where Melioidosis Is Highly Endemic. Clin Vaccine Immunol 2013;20:759–60. https://doi.org/10.1128/CVI.00021-13.
  18. Heymann DL, editor. Control of Communicable Diseases Manual. American Public Health Association; 2015. https://doi.org/10.2105/CCDM.2745.

Last updated: 10 August 2023