Melioidosis (Burkholderia pseudomallei)
2023 Case Definition

Background

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. Person-to-person transmission is extremely rare. B. pseudomallei infection has been identified in humans and multiple animal species. The median incubation period is 9 days but ranges from a few hours to decades after exposure. There is no vaccine, and even with treatment, case fatality rates range from 10-50%.¹

Melioidosis may present as a localized infection, pneumonia, bacteremia, or disseminated infection. Patients generally present with acute illness, but 15% present with chronic infection, with symptoms lasting over two months.² Clinical presentation may overlap with other diseases, complicating the diagnosis.³

Clinical Criteria

In the absence of a more likely diagnosis, at least one of the following signs or symptoms:

• Fever (temperature > 38.0°C [100.4°F])
• Muscle aches
• Ulcer
• Nodule
• Skin abscess
• Pneumonia
• Headache
• Chest pain
• Anorexia
• Respiratory distress
• Abdominal discomfort
• Joint pain
• Disorientation
• Weight loss
• Seizure
• Organ abscess (liver, lung, spleen, prostate, or brain)
• Encephalomyelitis/meningitis/extra-meningeal disease

Laboratory Criteria

Confirmatory laboratory evidence:

• Isolation of B. pseudomallei from a clinical specimen

Presumptive laboratory evidence:

• Evidence of a fourfold or greater rise in B. pseudomallei antibody titer by indirect hemagglutination assay (IHA) between acute- and convalescent-phase serum specimens obtained at least two weeks apart, OR
• Evidence of B. pseudomallei deoxyribonucleic acid (DNA) (for example, by Laboratory Response Network [LRN]-validated nucleic acid amplification test) in a clinical specimen

Supportive laboratory evidence:

• Single B. pseudomallei total antibody titer of greater than or equal to 1:40 by serology in one or more serum specimens

Note: The categorical labels used here to stratify laboratory evidence are intended to support the standardization of case classifications for public health surveillance. The categorical labels should not be used to interpret the utility or validity of any laboratory test methodology.

Epidemiologic Linkage

A person with at least one of the following findings:

• History of travel to or residence in a region endemic for melioidosis, OR
• Known exposure to B. pseudomallei as a result of intentional release or known product/source exposure (outside of laboratory), OR
• Known exposure to B. pseudomallei as a result of an occupational risk (i.e., laboratory exposure)

Criteria to Distinguish a New Case from an Existing Case

An infection would be counted as a new infection if a person is culture-positive within an 18-month time period with an isolate that is distinct from the previous infection by whole genome sequencing.

Note: Recurrent melioidosis can be defined as a re-presentation with B. pseudomallei culture-positive clinical disease occurring <18 months following initial diagnosis and after the time designated for treatment completion (both intravenous and oral phases) for the previous episode, irrespective of whether the patient was adherent to the therapy or initially lost to follow-up. Recurrent cases will not be counted as a new case for surveillance purposes. Epidemiological and exposure information can be used to determine if it is a new or recurrent infection, as can whole genome sequencing, if an isolate is available.

Suspect

• Meets clinical criteria AND supportive laboratory evidence AND epidemiologic linkage.
• Meets vital records criteria AND supportive laboratory evidence AND epidemiologic linkage.
• Meets other criteria AND supportive laboratory evidence AND epidemiologic linkage.

Probable

• Meets clinical criteria AND presumptive laboratory evidence AND epidemiologic linkage.
• Meets vital records criteria AND presumptive laboratory evidence AND epidemiologic linkage.
• Meets other criteria AND presumptive laboratory evidence AND epidemiologic linkage.

Confirmed

• Meets confirmatory laboratory evidence.

• A person whose healthcare record contains a recent diagnosis of melioidosis

 Vital Records Criteria

• A person whose death certificate lists melioidosis as a cause of death or a significant condition contributing to death

• Melioidosis (Burkholderia pseudomallei) | 2012 Case Definition