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Since 2015, when a Zika virus (ZIKV) epidemic spread through South America and the Caribbean, bringing neurologic sequelae including congenital microcephaly, transfusion-transmitted infection (TTI) has been a concern. Individual donor nucleic acid testing (ID-NAT) for ZIKV was instituted for donated blood from Puerto Rico in March 2016. This testing was extended to all 50 states and Washington D.C. later that year. Testing identified 257 ZIKV RNA positive donations in Puerto Rico and 54 in the rest of the U.S., at an estimated cost of about $5.3 million for each interdicted ZIKV positive unit of blood. In July 2018, the FDA recommended replacement of ID-NAT with mini-pool testing (MP-NAT) as a first step.
Researchers constructed a recipient-level microsimulation model of these blood screening practices to inform a cost-benefit analysis. They varied the model to account for seasonal variation in prevalence of mosquitos and ZIKV, geographic source of the donation, and travel histories to endemic areas.
Even with a highly inflated acceptable cost per quality-adjusted life years gained of $1 million, universal screening using ID-NAT was not cost-effective in the 50 states and Washington D.C. In Puerto Rico, ID-NAT was cost-effective during the initial season, but not compared with alternative methods such as MP-NAT. At current levels of ZIKV prevalence, no screening measures, outside of those targeted to a high-risk population, will be cost-effective.
Russell WA et al. Screening the blood supply for Zika virus in the 50 U.S. states and Puerto Rico: A cost-effectiveness analysis. Ann Intern Med 2019 Jan 8; [e-pub]. (https://doi.org/10.7326/M18-2238)
Ellingson KD and Kuehnert MJ.Blood safety and emerging infections: Balancing risks and costs. Ann Intern Med 2019 Jan 8; [e-pub]. (https://doi.org/10.7326/M18-3527)
Comment
Statistical models, as good as they can be, are just that. As we used to say in the early days of AIDS, statistics are patients without the tears. The goals should be to identify high-risk recipient populations (e.g., pregnant women receiving many units from endemic areas) for which screening would be cost-effective. As an excellent editorial emphasizes, infections with ZIKV and other arboviruses are dynamic situations with variability in almost every aspect of transmission. Improving vector control and screening methods will be vital in protecting the most people at the lowest cost.