Emerging infectious disease outbreaks: estimating disease risk in Australian blood donors travelling overseas.

BACKGROUND AND OBJECTIVES: International travel assists spread of infectious pathogens. Australians regularly travel to South-eastern Asia and the isles of the South Pacific, where they may become infected with infectious agents, such as dengue (DENV), chikungunya (CHIKV) and Zika (ZIKV) viruses that pose a potential risk to transfusion safety. In Australia, donors are temporarily restricted from donating for fresh component manufacture following travel to many countries, including those in this study. We aimed to estimate the unmitigated transfusion-transmission (TT) risk from donors travelling internationally to areas affected by emerging infectious diseases. MATERIALS AND METHODS: We used the European Up-Front Risk Assessment Tool, with travel and notification data, to estimate the TT risk from donors travelling to areas affected by disease outbreaks: Fiji (DENV), Bali (DENV), Phuket (DENV), Indonesia (CHIKV) and French Polynesia (ZIKV). RESULTS: We predict minimal risk from travel, with the annual unmitigated risk of an infected component being released varying from 1 in 1·43 million to <1 in one billion and the risk of severe consequences ranging from 1 in 130 million to <1 in one billion. CONCLUSION: The predicted unmitigated likelihood of infection in blood components manufactured from donors travelling to the above-mentioned areas was very low, with the possibility of severe consequences in a transfusion recipient even smaller. Given the increasing demand for plasma products in Australia, the current strategy of restricting donors returning from select infectious disease outbreak areas to source plasma collection provides a simple and effective risk management approach.

Reconsideration of blood donation testing strategy for human T-cell lymphotropic virus in Australia.

BACKGROUND AND OBJECTIVES: Universal testing of blood donations for human T-cell lymphotropic virus (HTLV) in Australia may no longer be appropriate given the low prevalence of HTLV infection and the mitigating effect of universal leucodepletion for cellular components. This study aimed to determine the most appropriate HTLV testing strategy using the Risk-Based Decision-Making Framework for Blood Safety. MATERIALS AND METHODS: The risk of HTLV transfusion-transmission using three testing strategies (universal, new-donor and no testing) and cost-effectiveness of the first two strategies were assessed using adaptations of published mathematical models. RESULTS: The overall prevalence for 2004-2014 was three HTLV-positives per million donations. It was estimated that annually, universal testing incurred a cost of approximately AUD $3 million and prevented 83 HTLV-positive cellular components from being issued, and new-donor testing cost approximately $225 000 and prevented 81 components. The number of cases of transfusion-transmitted HTLV and HTLV-associated disease prevented per year by universal and new-donor testing was essentially equivalent. According to preset risk thresholds, the risk of transfusion-transmission was negligible for universal and new-donor testing, and minimal without testing. CONCLUSION: Transfusion-transmission of HTLV is a minimal risk in Australia even without testing. However, any revision of testing strategy must consider not only risk and cost-effectiveness, but also stakeholder, ethical and regulatory perspectives. Considering all relevant criteria, new-donor testing is judged the optimal strategy because it is able to achieve almost the same outcomes as universal testing, at a fraction of the cost.

Hepatitis E virus RNA in Australian blood donors: prevalence and risk assessment.

BACKGROUND AND OBJECTIVES: Hepatitis E virus (HEV) is a known transfusion-transmissible agent. HEV infection has increased in prevalence in many developed nations with RNA detection in donors as high as 1 in 600. A high proportion of HEV infections are asymptomatic and therefore not interdicted by donor exclusion criteria. To manage the HEV transfusion-transmission (TT) risk some developed nations have implemented HEV RNA screening. In Australia, HEV is rarely notified; although locally acquired infections have been reported, and the burden of disease is unknown. The purpose of this study was to determine the frequency of HEV infection in Australian donors and associated TT risk. MATERIALS AND METHODS: Plasma samples (n = 74 131) were collected from whole blood donors during 2016 and screened for HEV RNA by transcription-mediated amplification (TMA) in pools of six. Individual TMA reactive samples were confirmed by RT-PCR and, if positive, viral load determined. Prevalence data from the study were used to model the HEV-TT risk. RESULTS: One sample in 74 131 (95% CI: 1 in 1 481 781 to 1 in 15 031) was confirmed positive for HEV RNA, with an estimated viral load of 180 IU/ml, which is below that typically associated with TT. Using a transmission-risk model, we estimated the risk of an adverse outcome associated with TT-HEV of approximately 1 in 3·5 million components transfused. CONCLUSION: Hepatitis E virus viremia is rare in Australia and lower than the published RNA prevalence estimates of other developed countries. The risk of TT-HEV adverse outcomes is negligible, and HEV RNA donor screening is not currently indicated.

Refining the risk estimate for transfusion-transmission of occult hepatitis B virus.

BACKGROUND AND OBJECTIVES: We previously published a model to estimate the residual risk (RR) for occult hepatitis B infection (OBI) in the absence of universal anti-HBc testing. To incorporate new information on the epidemiology of OBI, we describe model refinements and estimate a more accurate HBV RR due to OBI in Australia. MATERIALS AND METHODS: In our original model, the OBI risk, p(OBI), was defined by the rate of 'non-detection' by the HBV DNA screening test in use, p(NAT non-detection), and the average infectivity of blood components from OBI donors, p(transmission). We revised the model by integrating three refinements: that donations with anti-HBs levels of >10 IU/l, or donations solely for manufactured plasma products, be excluded from the risk calculation, and an updated estimate of p(transmission). RESULTS: Refining our OBI RR model resulted in a more than 10-fold reduction in the reported RR risk to recipients from OBI in our donor population. Based on the use of a common data set, the mean OBI RR risk decreased from 1 in 374 354 donations (95% CI: 1 in 191 940-1 072 681) to 1 in 3 984 033 (95% CI: 1 in 1 146 188-65 268 257) for the refined model. CONCLUSION: Our model refinements provide a more realistic measure of the HBV RR in the donor population. Unlike the previous model, the new model demonstrates that the risk of HBV due to OBI in the Australian blood donor population is negligible, and further potentially cost-ineffective risk management strategies are not currently warranted.

Re-evaluating the residual risk of transfusion-transmitted Ross River virus infection.

BACKGROUND AND OBJECTIVES: Ross River virus (RRV) is an enveloped, RNA alphavirus in the same antigenic group as chikungunya virus. Australia records an annual average of 5000 laboratory-confirmed RRV infections. While RRV is currently geographically restricted to the Western Pacific, the capacity of arboviruses for rapid expansion is well established. The first case of RRV transfusion-transmission was recently described prompting a comprehensive risk assessment. MATERIALS AND METHODS: To estimate the RRV residual risk, we applied laboratory-confirmed RRV notifications to two published models. This modelling generated point estimates for the risk of viraemia in the donor population, the risk of collecting a viraemic donation and the predicted number of infected components. RESULTS: The EUFRAT model estimated the risk of infection in donors as one in 95 039 (one in 311 328 to one in 32 399) to one in 14 943 (one in 48 593 to one in 5094). The point estimate for collecting a RRV viraemic donation varied from one in 166 486 (one in 659 078 to one in 49 158) (annualized national risk) to one in 26 117 (one in 103 628 to one in 7729) (area of high transmission). The modelling predicted 8-11 RRV-infected labile blood components issued in Australia during a 1-year period. CONCLUSION: Considering the uncertainty in the modelled estimates, the unknown rate of RRV donor viraemia and the low severity of any recipient RRV infection, additional risk management for RRV in Australia will initially be restricted to strengthening the messaging to donors regarding prompt reporting of any postdonation illnesses.