Infectious diseasesepidemiology and surveillance

Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures | Additional sources of information

Victorian statutory requirement

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.

School exclusion is not required.

Infectious agent

Burkholderia pseudomallei are small gram-negative, aerobic bacillus. It was previously named Pseudomonas pseudomallei or Whitmore’s bacillus.

Identification

Clinical features
Pneumonia is the most common clinical presentation of melioidosis, ranging from a mild respiratory illness to a severe pneumonia with septicaemia, with a mortality rate often over 50%. 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 these people the infection can re-activate from a latent form many years later.

Method of diagnosis
A definitive diagnosis of melioidosis can only be made by isolation of the organism from the respiratory tract, lung, blood or other sites.

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.

Incubation period

Australian data suggests an incubation period of 1–21 days. This can be prolonged in infections which initially become latent.

Public health significance & occurrence

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. The incidence of 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%. The majority of cases in northern Australia occur during the wet season in November to April. Disease can affect all ages but is more common in adults and predominantly occurs in males and Australian Aboriginals. Risk factors for disease include diabetes, chronic lung and renal disease and excess alcohol consumption.

Reservoir

Burkholderia pseudomallei have been found in soil and water in tropical regions of northern Australia and South East Asia.

Mode of transmission

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

Period of communicability

The disease is only very rarely transmitted person to person.

Susceptibility & resistance

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

Control measures

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

Control of case
A history of travel to northern Australia or tropical regions of South East Asia should be determined.

Initial intensive antibiotic therapy usually consists of trimethoprim/sulfamethoxazole with ceftazidime, meropenem, or imipenem. The trimethoprim/sulfamethoxazole component is usually continued for three months to ensure eradication. Consult the current version of Therapeutic guidelines: antibiotic (Therapeutic Guidelines Limited). 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
Investigation of potential sources is important. Human carriers are not known.

Control of environment
Not applicable.

Outbreak measures

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 of Health for further investigation.

Additional sources of information

• Currie, BJ, Fisher, DA, Howard, DM, Burrow, JNC et al. 2000, ‘Endemic melioidosis in tropical northern Australia; a ten year prospective study and review of the literature’, Clin Infect Dis, vol. 31, pp. 981–986.
• Currie, BJ 2000 ‘Melioidosis: an Australian perspective of an emerging infectious disease’, Recent Adv Microbiol, vol. 8, pp. 1–75.
• Currie, BJ, Fisher, DA, Howard, DM, Burrow, JNC et al. 2000, ‘The epidemiology of melioidosis in Australia and Papua New Guinea’, Acta Tropica, vol. 74, pp. 121–127.
• Northern Territory Centre for Disease Control