David D. Blaney, Jay E. Gee
Burkholderia pseudomallei, a saprophytic gram-negative bacillus, is the causative agent of melioidosis. The bacteria are found in soil and water, widely distributed in tropical and subtropical countries.
Transmission can occur through subcutaneous inoculation, ingestion, or inhalation; person-to-person transmission is extremely rare but may occur through contact with the blood or body fluids of an infected person.
Melioidosis is endemic to Southeast Asia, Papua New Guinea, much of the Indian subcontinent, southern China, Hong Kong, and Taiwan and is considered highly endemic to northeast Thailand, Malaysia, Singapore, and northern Australia. Sporadic cases have been reported among residents of or travelers to Aruba, Colombia, Costa Rica, El Salvador, Guatemala, Guadeloupe, Honduras, Martinique, Mexico, Panama, Venezuela, and many other countries in the Americas, as well as Puerto Rico. In northeastern Brazil, clusters of melioidosis have been reported. The true extent of the distribution of the bacteria remains unknown and is considered underreported or unrecognized in many tropical and subtropical areas, and more than 165,000 cases are estimated to occur annually.
The risk is highest for adventure travelers, ecotourists, military personnel, construction and resource extraction workers, and other people whose contact with contaminated soil or water may expose them to the bacteria; infections have been reported in people who have spent less than a week in an endemic area. Cases, especially presenting as pneumonias, are often associated with periods of high rainfall such as during typhoons or the monsoon season. Risk factors for invasive melioidosis include diabetes, excessive alcohol use, chronic renal disease, chronic lung disease (such as cystic fibrosis or chronic obstructive pulmonary disease), thalassemia, and malignancy or other non-HIV-related immune suppression.
Incubation period is generally 1–21 days; with a high inoculum, symptoms can develop in a few hours. Melioidosis may also remain latent for months or years before symptoms develop. Melioidosis may occur as a subclinical infection, localized infection (such as cutaneous abscess), pneumonia, meningoencephalitis, sepsis, or chronic suppurative infection. The latter may mimic tuberculosis, with fever, weight loss, productive cough, and upper lobe infiltrate, with or without cavitation. More than 50% of cases present with pneumonia.
Culture of B. pseudomallei from blood, sputum, pus, urine, synovial fluid, peritoneal fluid, or pericardial fluid is diagnostic. Indirect hemagglutination assay is a widely used serologic test but is not considered confirmatory. Diagnostic assistance is available through CDC (www.cdc.gov/ncezid/dhcpp/bacterial_special/zoonoses_lab.html).
Intravenous ceftazidime, or meropenem for severe cases with sepsis, is typically used for initial treatment, for a minimum of 14 days; depending on response to therapy, this initial treatment may be extended for up to 8 weeks. This is usually followed by 3–6 months of eradication treatment with an oral agent such as trimethoprim-sulfamethoxazole. Relapse may be seen, especially in patients who received a shorter-than-recommended course of therapy.
Travelers should use personal protective equipment such as waterproof boots and gloves to protect against contact with soil and water in endemic areas and thoroughly clean skin lacerations, abrasions, or burns contaminated with soil or surface water.
CDC website: www.cdc.gov/melioidosis
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