VIROLOGYHTLV-1 is rare in Far North Queensland despite a significant burden of classically associated diseases
Introduction
Human T-cell lymphotropic virus type 1 (HTLV-1) is an oncogenic retrovirus endemic to Australia. The prevalence in Indigenous people living in central Australia is amongst the highest in the world,1 which has led some authors to suggest that the clinical burden of HTLV-1 may be underestimated in Australia.2 This has resulted in calls for increased testing for HTLV-1, to better characterise the epidemiology of the infection and to inform prevention strategies.3, 4
Far North Queensland (FNQ) shares many similarities with central Australia. Approximately 42% of Indigenous Australians in FNQ live in remote communities where there is reduced access to healthcare and significant socioeconomic disadvantage. The Australian Bureau of Statistics' Socio-Economic Indexes for Areas places 80% of the Torres Strait Islands and Cape York Peninsula population in the lowest two socioeconomic quintiles.5, 6, 7
The prevalence of HTLV-1 in FNQ has not been reported, but diseases that have an established connection to the virus—T-cell leukaemia/lymphoma, myelopathy and scabies—are all seen locally, with the burden of scabies particularly significant.8 Other conditions that have been linked to HTLV-1 infection, including bronchiectasis, polymyositis and arthritis are also common.8, 9 This study was performed to determine the prevalence of HTLV-1 infection in FNQ, and the attributable burden of disease. Given recent calls to increase testing for HTLV-1, the study also aimed to assess local clinicians' awareness of the virus.
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Methods
We reviewed all HTLV-1 serology tests requested in the public health system in FNQ between January 1999 and December 2016 using Queensland Health's laboratory electronic results database. For each test performed the person's demographics, the rationale for testing and the test's result were recorded. The population of FNQ has grown from 222,451 in 1999 to 279,354 people in 2016, 15% of whom identify as Indigenous Australians.6, 7, 10 Over the study period, the following assays were used: HTLV1
Results
During the study period, 444 tests were performed on 409 people who had a median age of 50 years (interquartile range 37–60 years, range 2–91 years); 217 (53%) were male; 171 (42%) identified as Indigenous Australians. The annual number of tests increased from one test in 1999 to 126 tests in 2016 (p for trend < 0.001) (Fig. 1). People from throughout FNQ, including people living in remote communities were tested (Fig. 2). HTLV-1 serological testing most commonly occurred in the setting of a
Discussion
Diseases that have been associated with HTLV-1 are common in FNQ, but the infection itself is extremely rare. In the last 18 years, only four cases of HTLV-1 infection have been identified, three of which occurred in the same family, two of which were asymptomatic. This reported low prevalence does not appear to be explained by inadequate testing as the number of serology requests performed annually has increased significantly. It also does not appear to be explained by a lack of awareness, as
Conclusions
In summary, while there is a significant burden of bronchiectasis and skin disease in FNQ, this appears to be unrelated to HTLV-1 infection, which is extremely rare in the region. Despite targeted testing of patients with haematological malignancies and myelopathy, only a single case has been identified in patients with these two conditions in the last 18 years. Local clinicians appear to be aware of the disease and are testing and contact tracing appropriately. A greater focus on blood borne
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