Melioidosis

Overview

Melioidosis is caused by the environmental bacterium Burkholderia pseudomallei (B. pseudomallei). Infection typically occurs through direct contact with contaminated soil or water via subcutaneous inoculation, ingestion, or inhalation. Melioidosis may present as a localised infection, pneumonia, bacteraemia, or disseminated infection.

Disease epidemiology

The disease is endemic to Southeast Asia and Northern Australia where B. pseudomallei is found in soil and water. Cases have been reported in Singapore and other parts of the world, including Asia, the Pacific, the Americas, the Caribbean, and the Middle East.

Pathogen(s)

Burkholderia pseudomallei.

Transmission

Transmission of melioidosis occurs through:

• Direct inoculation of contaminated soil or water through small cuts or abrasions

• Inhalation of contaminated soil dust

• Ingestion or aspiration of contaminated water

Incubation period: Typically 9 days; range is 1 to 21 days. May remain latent for months to years before symptoms develop.

Infectious period: Not considered contagious; person-to-person spread is extremely rare.

Clinical features

The presentation of Melioidosis is variable and can mimic many other conditions (e.g. tuberculosis). Melioidosis infections can be subclinical, localised or disseminated. Common presentations include:

• Pneumonia (most common);

• Localised skin ulcers or abscesses;

• Osteomyelitis; or

• Meningoencephalitis

Depending on the site of infection, common symptoms that patients may experience are fever, headache, cough, chest pain, myalgia.

It should also be considered as a differential in a patient presenting with visceral abscesses (e.g. liver, spleen, kidney, or prostate). Involvement of joints, bones, viscera, lymph nodes, skin, or brain are also possible. Patients are often bacteraemic and can develop a fulminant infection with septic shock. The mortality rate is high in these cases. Some patients may experience relapses even after appropriate antibiotic therapy has been administered for the initial infection.

Risk factors

Risk factors include:

• Exposure to soil or surface water in occupational (e.g. military, farming, or construction work), or recreational (e.g. adventure travellers) activities;

• Comorbidities such as diabetes mellitus, chronic renal disease, chronic lung disease (like chronic obstructive pulmonary disease (COPD), or bronchiectasis, liver disease or thalassaemia)

• Cancer, or another condition that weakens the immune system

• Heavy alcohol use

Diagnosis 

Melioidosis is diagnosed when a laboratory test detects B. pseudomallei in samples from blood, respiratory specimens such as sputum, throat swabs, wound specimens, urine, or fluid obtained from infected site, via PCR or bacterial culture.

Serology (e.g. indirect haemagglutination test) is not a reliable method of diagnosis.

Treatment and management

Patients generally require long courses of antibiotics.

Treatment consists of an initial intensive therapy, followed by an oral eradication therapy. In the initial intensive phase of therapy, intravenous antibiotics (ceftazidime or meropenem) are given. This is followed by oral eradication therapy, trimethoprim-sulfamethoxazole (TMP-SMX) or amoxicillin/clavulanic acid (co-amoxiclav). The treatment duration varies depending on disease severity, and patient’s overall health, immune status and response.

It is important to ensure that the antibiotics are adhered to for the length of time prescribed, to prevent early recrudescence or subsequent relapse.

Abscesses should be drained when possible.

Precaution, prevention, and control

Standard precautions apply in healthcare settings. Post-exposure prophylaxis (such as TMP-SMX (first choice) or co-amoxiclav (second-line choice)) should be given to laboratory personnel with high risk of exposure or vulnerability to B. pseudomallei for 21 days.

Patients with known risk factors should cover all cuts and minimise contact with soil and surface water. Protective clothing (gloves and boots) is recommended for those with occupational exposure to soil and water. In endemic areas, skin wounds that have become contaminated with soil or surface water should be immediately and thoroughly cleaned. 

There is no available vaccine for melioidosis.

Notification

Melioidosis is a notifiable disease under the Infectious Diseases Act.

Who should notify:

• Laboratories

When to notify:

• Laboratories – upon laboratory confirmation

How to notify:

• Please refer to the Infectious Disease Notification ↗ (opens in new tab) for more information.

Notification timeline:

• Within 72 hours

Resources

Please refer to the Weekly Infectious Diseases Bulletin for the numbers of confirmed Melioidosis cases in Singapore.

For more information on Melioidosis, please refer to the Centers for Disease Control and Prevention ↗ (opens in new tab) website.

For general travel advisory, please refer to Health Advice for Travellers.