Melioidosis, most common in Southeast Asia and northern Australia, is caused by the environmental gram-negative bacillus Burkholderia pseudomallei. The latest review in our Medical Progress series considers recent developments in pathogenesis, diagnostics, and treatment.
Melioidosis, caused by the environmental gram-negative bacillus Burkholderia pseudomallei, is classically characterized by pneumonia and multiple abscesses, with a mortality rate of up to 40%. It is an important cause of community-acquired sepsis in Southeast Asia and northern Australia.
• Where is melioidosis endemic?
Among the major regions where melioidosis is endemic, the Top End of the Northern Territory in Australia and northeast Thailand represent hot spots, with annual incidence rates of up to 50 cases per 100,000 people. Melioidosis is the third most common cause of death from infectious disease in northeast Thailand, exceeded only by HIV infection and tuberculosis. Malaysia, Singapore, Vietnam, Cambodia, and Laos are also endemic regions. Reports have expanded the endemic zone to areas of the Indian subcontinent, southern China, Hong Kong, Taiwan, various Pacific and Indian Ocean islands, and parts of the Americas.
• How is melioidosis transmitted and what are the risk factors for acquiring infection?
Melioidosis primarily affects persons who are in regular contact with soil and water. Infection results from percutaneous inoculation (e.g., by means of a penetrating injury or open wound), inhalation (e.g., during severe weather or as a result of deliberate release), or ingestion (e.g., through contaminated food or water). Melioidosis is predominantly seasonal; 75 to 81% of cases occur during the rainy season. Incidence peaks between 40 and 60 years of age, but melioidosis is well recognized in children. Melioidosis has been transmitted to infants through breast milk from mothers with mastitis. Since up to 80% of patients with melioidosis have one or more risk factors for the disease, it has been suggested that melioidosis should be considered an opportunistic infection that is unlikely to have a fatal outcome in a previously healthy person, provided that the infection is diagnosed early and appropriate antibiotic agents and intensive care resources are available.
Morning Report Questions
Q: What are the clinical manifestations of melioidosis?
A: In a descriptive study involving 540 patients in tropical Australia over a 20-year period, the primary presenting feature was pneumonia (in 51% of patients), followed by genitourinary infection (in 14%), skin infection (in 13%), bacteremia without evident focus (in 11%), septic arthritis or osteomyelitis (in 4%), and neurologic involvement (in 3%). Over half of patients have bacteremia on presentation, and septic shock develops in approximately one fifth. Internal-organ abscesses and secondary foci in the lungs, joints, or both are common.
Q: How is melioidosis treated and what is the expected course?
A: Melioidosis has a notoriously protracted course; cure is difficult without a prolonged course of appropriate antibiotics. The treatment of melioidosis consists of an intensive phase of 10 to 14 days of ceftazidime, meropenem, or imipenem administered intravenously, followed by oral eradication therapy, usually with trimethoprim-sulfamethoxazole (TMP-SMX) for 3 to 6 months.
B. Pseudomallei is inherently resistant to penicillin, ampicillin, first-generation and second-generation cephalosporins, gentamicin, tobramycin, streptomycin, and polymyxin.