West Nile virus transfusion-transmission risk in Australia associated with a seasonal outbreak in the United States

Background West Nile virus (WNV) is a potentially transfusion-transmissible virus endemic in the US. The aim of this study was to estimate the monthly WNV transfusion transmission (TT) risk in Australia associated with donors returning from the US in 2018 and consider the implications for mitigation strategies. Study Design and Methods We used a probabilistic risk model to estimate the monthly WNV TT risks for each outbreak state/district in the US for the 2018 transmission season and the cumulative monthly risk for all US states/districts. Results The highest monthly cumulative transfusion risk in Australia occurred in August 2018 when 746 West Nile neuroinvasive disease cases were reported in the US and the estimated mean WNV TT risk in Australia was 1 in 1.0 x 10(8) donations (95% confidence interval [CI]: 1.6 x 10(8)-7.0 x 10(7)). The highest risk during August was associated with California, with a mean risk of 1 in 4.1 x 10(8) donations (95% CI: 2.9 x 10(8)-6.6 x 10(8)), representing 24% of the total risk in Australia. The cumulative TT risk in Australia for the other 11 months varied from 1 in 1.5 x 10(8) donations (95% CI: 2.3 x 10(8)-1.0 x 10(8)) in September to 1 in 3.9 x 10(10) donations (95% CI: 6.1 x 10(10)-2.7 x 10(10)) in February. Discussion Our modeling indicates that the WNV TT risk in Australia associated with seasonal outbreaks in the US is extremely small and may not warrant donation restrictions for donors returning from the US.