American Red Cross West Nile Virus Testing
Testing began on 5/23/2003; Updated on: 10/14/2021
This presentation contains information for West Nile Virus (WNV) Testing. It includes not only American Red Cross (ARC) information, but also information from the AABB West Nile Virus Biovigilance Network and the Centers for Disease Control and Prevention (CDC), National Center for Emerging and Zoonotic Infectious Diseases (NCEZID), Division of Vector-Borne Diseases (DVBD).
Donations that test reactive for WNV are classified as either a Presumed Viremic Donation (PVD) or non-PVD. A Presumed Viremic Donation (PVD) is defined as: 1) a WNV-initially reactive donation with a signal-to-cutoff (S/CO) ratio of greater than or equal to 17 using the WNV Transcription-Mediated Amplification (TMA) Assay or 2) a WNV-initially reactive donation with an S/CO ratio of less than 17 if upon repeat testing the sample is repeatedly reactive.
American Red Cross WNV TMA testing is routinely performed using minipools comprised of 16 samples. When WNV activity is identified in a geographic area from: a WNV-reactive donation, human WNV activity or mosquito WNV activity, testing is converted to Individual Donation Nucleic Acid Testing (ID-NAT). This is termed as “triggering for WNV ID-NAT” and the area of trigger is defined as a 50-mile radius surrounding a single zip code.
Additional testing is performed to further classify WNV reactives as confirmed or non-confirmed. PVDs have a 95% or greater chance of being confirmed by additional testing (repeat testing from an independent sample including the same or alternate WNV NAT and/or IgM reactivity at index or follow-up testing).
The “Current Red Cross Triggered Areas” map can be accessed online by hovering over the link in the header and selecting control & click. The online map is interactive and can be zoomed in/out.