Getting to know the unknown

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 × 10⁸ donations (95% confidence interval [CI]: 1.6 × 10⁸ -7.0 × 10⁷ ). The highest risk during August was associated with California, with a mean risk of 1 in 4.1 × 10⁸ donations (95% CI: 2.9 × 10⁸ -6.6 × 10⁸ ), 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 × 10⁸ donations (95% CI: 2.3 × 10⁸ -1.0 × 10⁸ ) in September to 1 in 3.9 × 10¹⁰ donations (95% CI: 6.1 × 10¹⁰ -2.7 × 10¹⁰ ) 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.

Modeling the West Nile virus transfusion transmission risk in a nonoutbreak country associated with traveling donors

BACKGROUND

West Nile virus (WNV) is a mosquito-borne virus and transfusion transmission (TT) has been demonstrated. The European Union and neighboring countries experience an annual transmission season.

STUDY DESIGN AND METHODS

We developed a novel probabilistic model to estimate the WNV TT risk in Australia attributable to returned donors who had travelled to the European Union and neighboring countries during the 2018. We estimated weekly WNV TT risks in Australia for each outbreak country and the cumulative risk for all countries.

RESULTS

Highest mean weekly TT risk in Australia attributable to donors returning from a specific outbreak country was 1 in 23.3 million (plausible range, 16.8-41.9 million) donations during Week 39 in Croatia. Highest mean weekly cumulative TT risk was 1 in 8.5 million donations (plausible range, 5.1-17.8 million) during Week 35.

CONCLUSIONS

The estimated TT risk in Australia attributable to returning donors from the European Union and neighboring countries in 2018 was very small, and additional risk mitigation strategies were not indicated. In the context of such low TT risks, a simpler but effective approach would be to monitor the number of weekly reported West Nile fever cases and implement risk modeling only when the reported cases reached a predefined number or trigger point.

Estimation of mosquito-borne and sexual transmission of Zika virus in Australia: Risks to blood transfusion safety

BACKGROUND

Since 2015, Zika virus (ZIKV) outbreaks have occurred in the Americas and the Pacific involving mosquito-borne and sexual transmission. ZIKV has also emerged as a risk to global blood transfusion safety. Aedes aegypti, a mosquito well established in north and some parts of central and southern Queensland, Australia, transmits ZIKV. Aedes albopictus, another potential ZIKV vector, is a threat to mainland Australia. Since these conditions create the potential for local transmission in Australia and a possible uncertainty in the effectiveness of blood donor risk-mitigation programs, we investigated the possible impact of mosquito-borne and sexual transmission of ZIKV in Australia on local blood transfusion safety.

METHODOLOGY/PRINCIPAL FINDINGS

We estimated 'best-' and 'worst-' case scenarios of monthly reproduction number (R0) for both transmission pathways of ZIKV from 1996-2015 in 11 urban or regional population centres, by varying epidemiological and entomological estimates. We then estimated the attack rate and subsequent number of infectious people to quantify the ZIKV transfusion-transmission risk using the European Up-Front Risk Assessment Tool. For all scenarios and with both vector species R0 was lower than one for ZIKV transmission. However, a higher risk of a sustained outbreak was estimated for Cairns, Rockhampton, Thursday Island, and theoretically in Darwin during the warmest months of the year. The yearly estimation of the risk of transmitting ZIKV infection by blood transfusion remained low through the study period for all locations, with the highest potential risk estimated in Darwin.

CONCLUSIONS/SIGNIFICANCE

Given the increasing demand for plasma products in Australia, the current strategy of restricting donors returning from infectious disease outbreak regions to source plasma collection provides a simple and effective risk management approach. However, if local transmission was suspected in the main urban centres of Australia, potentially facilitated by the geographic range expansion of Ae. aegypti or Ae. albopictus, this mitigation strategy would need urgent review.

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.

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.