Original Research Article Melioidosis in the Torres Strait Islands: an 11 year audit 2001-2012
AM S J
Dr. Kathrin Rac BMSc, MBBS Intern, Princess Alexandra Hospital
Kathrin is a recent graduate with an interest in neurosurgery. She is currently completing her Graduate Certificate in Research Methods. She enjoys reading, playing tennis, yoga and travelling.
Dr. Michael McLaughlin MBBS Intern, Cairns Base Hospital
Michael is a recent graduate with an interest in global, developmental and public health. He is currently completing his Masters in Public Health and Tropical Medicine.
Melioidosis is an infection of concern to global health. It is caused by the intracellular gram-negative bacterium Burkholderia pseudomallei, which is found in the soil and fresh waters of endemic regions. This study identified the average annual incidence of melioidosis in the Torres Strait region between 2001-2012, and compared this to one other similar study, which identified the average annual incidence between 1995-2000. Patient demographics, clinical presentation, outcomes and risk factors were compared to other available studies. In this retrospective study of melioidosis in the Torres Strait, 31 cases were identified over an 11-year period, representing an annual incidence of 37 cases per 100,0000 population. Of these cases, 84% recovered, 16% required intensive care unit (ICU) admission, 3% had a relapse and two patient deaths occurred. The mortality rate was 6.4%. Pneumonia accounted for fifteen presentations (48%) and splenic abscesses for ten presentations (32%), with nine patients presenting with septic arthritis of a joint (29%). Other presentations included hepatic (19%), prostatic (19%), renal (10%), skin (6%), pancreatic (3%), scrotal (3%) and spinal abscesses (3%). Four presented with bacteraemia alone (13%) and one case presented with urethritis (3%). Risk factors included diabetes mellitus (68%), excessive alcohol intake (35%), renal disease (12%), autoimmune disease (6%), malignancy (4%) and the use of immunosuppressive medication (2%).
Introduction Melioidosis is an infection caused by the intracellular gram-negative bacterium Burkholderia pseudomallei, which is found in the soil and fresh waters of endemic regions. [1] Endemic regions include Southeast Asia and Northern Australia, with peaks of infection occurring during the wet seasons. [2] Melioidosis is of global public health significance, and may be thought of as an emerging infection across tropical regions. [3] The Torres Strait is a tropical region comprised of 274 islands between the Cape York Peninsula of mainland Australia and Papua New Guinea (PNG). According to the 2006 Australian Bureau of Statistics (ABS) census data, the region has a total population of 7,624, with 82.5% identifying as Indigenous. [4] Half of this population is clustered within the central island group located closest to Thursday Island (TI), which is the commercial and governmental centre of the region. Hospital services are also centralised at TI, however, the closest tertiary referral centre for the Torres Strait region is the Cairns Base Hospital, located 800km south of TI. Melioidosis is endemic in the Torres Strait, with the most recent average annual incidence reported to be 42.7 cases per 100,000. [5] This is significantly greater than other centres such as Darwin, where the annual incidence was noted to be 19.6 cases per 100,000 between 1986 and 2008. [6] However, during periods of extreme climate, such as during years of significant heavy rainfall, this incidence dramatically increases. This was observed in Darwin between 2009 and 2010, during which the annual incidence increased to 50.2 cases per 100,000, as a result of a heavy wet season. [7] The variability in annual incidence
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highlights the significant relationship between the transmission of melioidosis and certain environmental factors, such as rainfall level. [1,2] The transmission of melioidosis most commonly occurs through percutaneous inoculation, and less commonly through inhalation, aspiration and ingestion. [2] A range of host and environmental factors must also exist for an individual to be infected. This includes reduced host immunity and the significant environmental exposure to the pathogen which occurs in endemic regions. [1] This was demonstrated in the study by Kanaphun et al. conducted in northeast Thailand, in which serological studies of 80% of the population exhibited positivity for antibodies against B. pseudomallei by four years of age. [18] There is clear significant environmental exposure in populations of northeast Thailand, yet only 20% of these children developed a symptomatic infection. [1,18] In addition, of the adults infected with symptomatic melioidosis, over 80% displayed reduced host immunity, with most affected by diabetes mellitus or renal failure. [8] In comparison, studies conducted in Australia demonstrated that most individuals were affected by excessive alcohol consumption and diabetes mellitus. [9] The clinical syndrome associated with the infection of B. pseudomallei is diverse and can affect a variety of organs. Both domestic and international literature overwhelmingly demonstrated the lung as the most commonly affected organ, with pneumonia being the most common clinical presentation of melioidosis. [7,9] Other clinical presentations include symptoms of septicaemia such as fever, malaise, pain in the joints or abdomen, which may be the result of abscess formation in the liver, prostate, kidney, skin or pancreas. The incubation period varies, as B. pseudomallei can remain dormant for a prolonged period of time. This makes it difficult to establish the exact period of infection. In most cases, a diagnosis of melioidosis is made through positive cultures demonstrating the growth of B. pseudomallei. Serological evidence can also be used to demonstrate past infections, or the presence of rising titres can provide a diagnosis in the absence of positive cultures. [2] Recurrence of melioidosis can occur in 15% of individuals within ten years of the primary infection, with 50% of these occurring within the first twelve months. [10] Overall, 25% of individuals with recurrence will die. [10] Risk factors for recurrence include severity of initial