Melioidosis

Notification requirement for melioidosis

Notification is not required, although it is recommended that cases of melioidosis with a history of travel to northern Australia be reported to public health units in the relevant state or territory.

Primary school and children’s services centres exclusion for melioidosis

Exclusion is not required.

Infectious agent of melioidosis

Burkholderia pseudomallei is a small Gram-negative aerobic bacillus. It was previously named Pseudomonas pseudomallei or Whitmore’s bacillus.

Identification of melioidosis

Clinical features

Pneumonia is the most common clinical presentation of melioidosis, ranging from a mild respiratory illness to severe pneumonia with septicaemia, with a mortality rate often more than 50 per cent. Other presentations include skin abscesses or ulcers; internal abscesses of the prostate, kidney, spleen and liver; fulminant septicaemia; and neurological illnesses, such as brainstem encephalitis and acute flaccid paralysis. Asymptomatic infection can occur, and in a small proportion of such cases the infection can reactivate from a latent form many years later. Chronic tuberculosis-like presentations can also exist. Pneumonia as the primary presentation is associated with the highest mortality.

Diagnosis

A definitive diagnosis of melioidosis can only be made by isolation of the organism from the upper or lower respiratory tract, blood or other sites. Swabs for melioidosis culture can be taken from the throat, the rectum and any wounds. Urine and sputum can also be cultured.

The likelihood of a bacterial diagnosis is increased by using selective culture media (modified Ashbrown’s broth), frequent sampling (sputum, throat, rectal and ulcer swabs) and collection of blood cultures.

Melioidosis serology with an indirect haemagglutination titre of > 1:40 is suggestive of past exposure, not specifically reflective of active infection.

Incubation period of melioidosis

Australian data suggests an incubation period of 1–21 days. This can be prolonged in infections that initially become latent, with reported latency periods of up to 62 years.

Public health significance and occurrence of melioidosis

Melioidosis is endemic in South-east Asia and northern Australia. It is now recognised in the northern areas of the Northern Territory as the most common cause of fatal community-acquired bacteraemic pneumonia, and as the most common cause of severe community-acquired sepsis in Thailand. Cases of melioidosis have also been documented from Papua New Guinea, Fiji and New Caledonia; the extent of endemicity in the Pacific islands remains to be defined. The incidence of the disease in Victorian residents is unknown.

In a 10-year prospective study in the Northern Territory, 252 cases were identified, with a case-fatality rate of 19 per cent. The majority of cases in northern Australia occur during the wet season from November to April. Disease can affect people of all ages but is more common in adults and predominantly occurs in males and Aboriginal or Torres Strait Islander people. Risk factors for disease include diabetes, chronic lung and renal disease and excessive alcohol consumption.

Reservoir of Burkholderia pseudomallei

Burkholderia pseudomallei has been found in soil and water in tropical regions of northern Australia and South-east Asia. Lung colonisation, rather than pathological infection, is rare and is associated only with cystic fibrosis or severe bronchiectasis.

Mode of transmission of Burkholderia pseudomallei

Infection is thought to be acquired through percutaneous inoculation, although inhalation and ingestion are also possible routes.

Period of communicability of melioidosis

The disease is only very rarely transmitted from person to person.

Susceptibility and resistance to melioidosis

Disease in humans is uncommon even among residents of epidemic areas who have close contact with soil or water containing the infectious agent. Approximately two-thirds of cases have a predisposing medical condition or represent recrudescence in asymptomatically infected individuals.

Control measures for melioidosis

Preventive measures

There is no vaccine available. Basic hygiene can help to limit the spread of many diseases, including melioidosis, and measures such as wearing shoes outside may prevent acquisition.

Control of case

A history of travel to northern Australia or tropical regions of South-east Asia should be ascertained.

Initial intensive antibiotic therapy consists of 2 weeks of ceftazidime or a carbapenem antibiotic, often combined with trimethroprim-sulfamethoxazole (TMP-SMX), followed by at least 3 months of TMP-SMX monotherapy. Treatment is usually considered for culture-positive patients. Consult the current version of Therapeutic guidelines: antibiotic. Specialist infectious disease advice should be sought for all cases.

Follow-up of cases and adherence to eradication therapy are critical to prevent relapse, which can be fatal.

Control of contacts

The investigation of potential sources is important. Human carriers are not known.

Control of environment

Not applicable.

Outbreak measures for melioidosis

Melioidosis has been identified as a potential bioterrorism agent. Any case or cases presenting without a clear history of exposure in an endemic area should be reported to the department for further investigation.

Additional sources of information

Currie, BJ 2000, ‘Melioidosis: an Australian perspective of an emerging infectious disease’, Recent Advances in Microbiology, vol. 8, pp. 1–75.