Donor screening assays more sensitive than diagnostic assays for Zika

^{Photo by Daniel Gay}

Blood in bags and vials

New research suggests assays used to screen donated blood for the Zika virus are more sensitive than assays used to help physicians diagnose Zika infection.

The study showed that donor screening assays could detect Zika virus RNA with greater sensitivity than diagnostic real-time polymerase chain reaction (RT-PCR) assays.

However, the evidence also indicated that increasing the volume of blood analyzed can increase the sensitivity of diagnostic assays.

This research was published in Transfusion in a special issue focusing on Zika and other transfusion-transmitted viruses.

The researchers compared 17 nucleic acid amplification technology assays used at 11 different labs. (Some of the 17 assays were actually the same assays used at different labs.)

One of the donor screening assays was the Procleix Zika virus assay, which was co-developed by Hologic, Inc. and Grifols Diagnostic Solutions, Inc. and used at Hologic.

The other donor screening assay was the cobas Zika test, which was developed by Roche Molecular Systems, Inc. and used in the company’s lab.

The RT-PCR diagnostic assays included the US Centers for Disease Control and Prevention’s (CDC) Singleplex (1087, 4481) and Trioplex assays—both low input (LI) and high input (HI)—which were used at the CDC labs in Puerto Rico (PR) and Fort Collins (FC).

Modified versions of the CDC’s assays were also used at the Blood Systems Research Institute (BSRI) in San Francisco, the University of California (UC) Davis, the Institut Louis Malarde (ILM) in French Polynesia, and 2 labs in Brazil—Fundação Pró-Sangue and Laboratório Richet.

The US Food and Drug Administration (FDA) used its own RT-PCR test, and the Etablissement Francais du Sang (EFS) in France used the Altona RealStar ZIKV RT-PCR assay.

Results

The various assays were used on plasma samples positive for 2 different strains of Zika virus—1 from Brazil and 1 from French Polynesia—as well as Zika-negative control samples.

The researchers found the donor screening assays provided comparable sensitivity and were more sensitive than each of the diagnostic RT-PCR assays.

So the team compared results with the 2 donor screening assays combined to results with the RT-PCR assays, which they grouped into 9 categories based on similar intended applications, methodologies, and results.

The 95% limit of detection (LOD₉₅) and 50% limit of detection (LOD₅₀) for the assays were as follows.

The researchers noted that the donor screening assays were about 10-fold to 100-fold more sensitive than the standard input RT-PCR assays.

However, the CDC’s assays were performed with low and high inputs of plasma. And increasing the sample input volume increased the limit of detection by 10-fold to 30-fold.

“The results of this study, that evaluated 17 Zika virus assays in 11 laboratories and documented excellent sensitivity of the 2 donor screening assays manufactured by Roche and Grifols, were critical to support the decision by the US Food and Drug Administration and blood industry to implement investigational screening of donors in Puerto Rico in April 2016 and the entire US by the end of 2016,” said study author Michael Busch, MD, PhD, of BSRI.

“Given the sensitivity of these assays, the FDA approved clinical trials using individual donation screening and rescinded earlier policies precluding transfusion of blood collected in Puerto Rico and deferral from donation by donors who had traveled to Zika risk countries throughout the US. This screening has detected over 350 infected blood donations in Puerto Rico and dozens of infected donations in the continental US.”