OPHEPR; Melioidosis - Profile for Healthcare Workers

Causative Agent: Melioidosis is caused by the gram-negative bacillus Burkholderia pseudomallei. The bacteria are widely distributed in the soil and water in Southeast Asia and northern Australia. Both humans and other susceptible animals may contract the disease.

Routes of Exposure: Humans are primarily exposed to melioidosis through direct contact with a contaminated source, such as soil or stagnant surface water.

Infective Dose & Infectivity: The infective dose is assumed to be low and all people are considered susceptible. In asymptomatic individuals severe injuries, burns, or debilitating disease may precipitate clinical onset of melioidosis.

Incubation Period: The incubation period can be as short as 2 days. However, years may elapse between the presumed exposure and the appearance of clinical disease.

Clinical Effects: The clinical manifestations of melioidosis include local skin infection, lung involvement, bacteremia, chronic suppurative infection in many organ systems, and neurologic infection. The most likely presentation due to bioterrorism would be pulmonary infection due to aerosolized bacteria. Inhalational melioidosis is an acute pyogenic process that can resemble plague pneumonia, with fever, severe systemic symptoms, and consolidative pneumonia. Secondary bacteremia can result in a papular or pustular rash that resembles smallpox lesions. Chest X-rays can show a variety of infiltrates, often upper lobe infiltrates that cavitate.

Lethality: Mortality from severe pneumonia and septicemia may be as high as 50%. In localized skin disease the mortality is low.

Transmissibility: Infection with B. pseudomallei generally occurs when contaminated soil or water comes in contact with lacerated or abraded skin. Melioidosis can also be acquired through aspiration or ingestion of water or inhalation of dust contaminated with the organism. Person-to-person transmission through direct contact may also be possible.

Primary contaminations & Methods of Dissemination: As a bioterrorism weapon, melioidosis would most likely be delivered via aerosolization.

Secondary Contamination & Persistence of organism: Only three cases of secondary infection have been reported. In one case it is thought that a caretaker acquired the disease from a patient with chronic melioidosis. The other two cases are believed to have occurred as a result of sexual contact following a chronic prostate infection.

Decontamination & Isolation:

Patients – Standard precautions should be practiced. Contact precautions should be used with sputum, sinus drainage, skin lesions and secretions.
Equipment, clothing & other objects – 0.5% hypochlorite solution (one part household bleach and 9 parts water = 0.5% solution) is effective for environmental decontamination.

Laboratory testing: Gram stain of lesion exudates reveals small gram-negative bacteria. These stain irregularly with methylene blue. A four-fold increase in titer supports the diagnosis of melioidosis. A single titer above 1:160 with a compatible clinical picture suggests active infection.

Therapeutic Treatment: The current treatment of choice for severe melioidosis is ceftazidime and trimethoprim-sulfamethoxazole, although other broad spectrum antibiotic regimens are being evaluated. After several weeks of IV therapy, prolonged oral antibiotic treatment of 3-5 months or more is required to decrease the chance of relapse.

Prophylactic Treatment: There is no vaccine available for human use. There is no pre-exposure or post exposure medication for preventing melioidosis, although trimethoprim-sulfamethoxazole has been suggested.

Differential Diagnosis: The differential diagnosis for severe pneumonia should include unusual organisms such as plague, tularemia, and inhalational anthrax. Considerations for acute febile pustular skin lesions include staphylococci, gonorrhea, secondary syphilis, ecthyma gangrenosum, and smallpox.

References:

Chin J. Control of Communicable Diseases Manual, Seventeenth Edition, American Public Health Association; 2000.
Marty AM. Melioidosis and Glanders In: Physician’s Guide to Terrorist Attack. Roy MJ, ed. Physician’s Guide to Terrorist Attack. Totowa, NJ: Humana Press, Inc.; 2004:143-159
Kortepeter M, Christopher G, Cieslak T, et al. Medical Management of Biological Casualties Handbook, U.S. Army Medical Research Institute of Infectious Diseases, U.S. Department of Defense; 2001: 37-42

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