Human T-lymphotropic virus-1 serology in the Northern Territory: 2008-2011

A retrospective observational study of human T-lymphotropic virus-1 (HTLV-1) serology requests made to the Northern Territory Government Pathology Service (NTGPS) between 2008 and 2011, was undertaken to review aspects of HTLV-1 sero-epidemiology and performance of the assays. A total of 5686 HTLV-1 serology requests, representing 3555 individual patients, were received during the study period; 368 HTLV-1 confirmed positive serology results were identified from the 3555 individual patients included in the sample. There was a distinct difference in the performance of the two antibody assays in use during this period, with the Serodia particle agglutination having a 5.7% indeterminate positivity rate compared to 18.1% indeterminate positivity rate of the Abbott HTLV 1/2 assay. We believe this is partially a serological anomaly related to current Australian western blot positive interpretative criteria, rather than false positive screening assay results. The majority (99.7%) of positive results occurred in Indigenous patients. The HTLV-1 positive rate varied geographically from a regional high of 51.7%, and falling inversely with distance from Central Australia. Patients with positive serology had a mean age of 49.9 (±13.9) years, with positivity occurring equally in males and females.