Screening Blood Donations for Zika, Costly With Low Yields

Screening the entire U.S. blood supply for Zika virus may not be worth the $42 million price tag. Fifteen months of screening all donations to the American Red Cross yielded only nine Zika-positive donors, according to a study published May 10 in the New England Journal of Medicine, and of these only four had an acute infection.

The American Red Cross processes more than 40 percent of the nation’s blood donations. In June 2016 the organization began screening for Zika RNA using the Procleix Zika Virus Assay on the Panther System (Grifols Diagnostic Solutions) under a Food and Drug- (FDA-) approved investigational-new-drug protocol in 16-member minipools. Testing began with donations from five southeastern U.S. states thought to be at high risk. In August 2016, in light of revised FDA guidance, the American Red Cross began testing all blood donations nationally and began the migration from minipool testing to individual donation testing using the same transcription-mediated amplification (TMA) technology.

Donations that initially were reactive were retested in triplicate with the same testing platform. Additional confirmatory testing of reactive donations involved real-time reverse-transcriptase polymerase chain reaction, IgM serologic testing, and red-cell TMA. To assess the sensitivity of minipool TMA, positive individual donations were tested in triplicate in exploratory 16-sample minipools that mixed the reactive donation with 15 nonreactive donations. Costs were calculated for testing conducted between June 2016 and September 2017. The American Red Cross and Grifols Diagnostic Solutions funded this analysis.

The researchers found that of the 4,325,889 donations that were screened over the 15-month period, 9 percent were initially tested in 24,611 minipools, with no reactive donations detected. Of the 3.9 million donations that were subsequently tested individually, 160 were initially reactive with nine confirmed as positive — a rate of confirmed Zika-positive donations of 1 per 480,654. The remaining 151 initially reactive donations were ultimately deemed nonreactive based on alternate nucleic acid testing, serologic testing, or additional TMA testing. Overall, testing yielded a positive predictive value, 5.6%; specificity, 99.997 percent.

Four of the nine confirmed-positive donations were IgM-negative, meaning the blood was collected before seroconversion had occurred. Three of these four donations had enough sample left over to be tested using minipool TMA and all three were reactive. The five confirmed, IgM–positive donations were nonreactive in TMA minipool testing and detection of Zika RNA at index using alternate nucleic acid testing was unsuccessful.

Each confirmed-positive donor consented to participate in the Zika Virus Follow-up Study and provided follow-up samples. Zika RNA levels in red cells ranged from 40 to 800,000 copies per milliliter and were detected up to 154 days after donation, versus 80 days in plasma at levels of 12 to 20,000 copies per milliliter.

Costs for minipool nucleic acid testing were $6, which is similar to that for other transfusion-transmitted viruses for which minipool nucleic acid testing is currently used, the authors say. Costs were $10 for individual-donation nucleic acid testing. Overall, the cost of Zika testing was approximately $41.7 million over the 15-month study period, or approximately $5.3 million per Zika RNA–positive donation.

The authors say this projects to $137 in annual screening costs nationally, which would pose “an additional strain” on the blood industry.

“The argument we’re trying to make is that Zika should be treated just like West Nile or HIV …  and not have to test each donation individually. Because it’s certainly a waste of resources and a waste of our capacity,” senior author Susan Stramer, from the American Red Cross, told STAT News.

Back in December 2017 the expert Blood Products Advisory Committee advised the  FDA that the blood supply operators be allowed to revert to pooled testing for Zika. But as of mid-May, the FDA hasn’t instituted the change.

“There is no doubt that Zika poses a major public health threat. However, the actual and perceived risks to the blood supply seem to be conflated,” writes Evan Block, M.B.Ch.B., from Johns Hopkins University in Baltimore, Md., in an accompanying editorial. Yet, Block and colleagues say, “Cessation of blood-donation screening may actually prove to be far more challenging than the decision to start. Indeed, there is no historical precedent for the termination of a blood-donation testing program for a given pathogen.”

Takeaway: Individual testing of all U.S. blood donations is costly with very low yield. The blood industry is awaiting a possible recommendation by the FDA to return to pooled testing.