The risk of dengue transmission by blood during a 2004 outbreak in Cairns, Australia

BACKGROUND: Dengue virus (DENV) is a Flavivirus transmitted by the Aedes mosquito. The related arbovirus, West Nile virus, has been shown to be transfusion transmitted, which, added to the four recorded dengue transfusion-associated cases, indicates that DENV is also transfusion transmitted. The purpose of this study was to assess the risk of transfusion-transmitted DENV during a 2004 outbreak in the Australian city of Cairns. STUDY DESIGN AND METHODS: A mathematical model was constructed to estimate the risk of transfusion-transmitted dengue. The model's central premise is that the transmission risk is proportional to the frequency of dengue-viremic donations and correlates with the incidence of asymptomatic dengue viremia among the population at large. RESULTS: The modeling predicted that the total number of DENV infections (clinical plus subclinical) among the population at large during the entire outbreak ranged from 156 to 569 with the epidemic peak occurring between February 8 and March 6, 2004. The overall transmission risk during the entire outbreak was estimated as 1 in 19,759 (range, 1 in 3404 to 75,486) peaking at 1 in 5968 (range 1 in 1028 to 22,800). CONCLUSION: By use of the most conservative estimates for key variables, the risk of collecting a viremic donation could have been as high as 1 in 1028 during the peak of the 2004 outbreak. The model can be used to determine transfusion transmission risk levels during DENV outbreaks and inform decisions as to when fresh component restriction measures are required to minimize transfusion transmission risk.