The analytical sensitivity of each primer set was determined in the single virus testing using FDA/CBER panels (kindly provided by Dr. Stephen Kerby, FDA/CBER) consisting of various amounts of the viruses (0-1,000 genome copies/ml) spiked into the ''normal'' human plasma. Panels for the following viruses were used in testing: HIV-1 (three different panels), HIV-2, HBV (based on genotype A), HCV (genotype 1b), and WNV (based on strain HU2002). These panels have been used for testing of commercially licensed NAT assays and their development was described previously [15] . Three separate HIV-1 RNA panels were used for testing. The first consisted of various amounts of an HIV-1 group M subtype B isolate: 0, 5, 10, 25, 50, 100, and 500 copies/ml. The second consisted of 25 samples representing various concentrations of HIV-1 groups O and N, and group M subtypes A, C, D, E, F and G: 10, 100 and 1,000 copies/ml for each virus. The third panel consisted of HIV-1 circulating recombinant forms (CRFs) AE and AG: 100, 1,000, and 10,000 copies/ml for each CRF. NP24 CAACTTCATCCACGTTTCACC a -to simplify the process of evaluation we used our primer names with sequential numbers, however some of the primers have been designed previously with their original names in the articles listed in the last column of this [25] [26] . HIV-1 groups and subtypes are based on designations reported by the NIH ARRRP. Low passage virus stocks were prepared and median tissue culture infective dose (TCID 50 )/ml of virus containing supernatant determined in fresh human PBMCs isolated as previously described [27] . Infectious unit (IU) of the virus stocks in TCID 50 s were titrated for each isolate and the number of IU used for viral RNA isolation and PCR was calculated based on the dilution factor (1:100) and ranged from ,10 to 2,500 or 1 to 3.4 log 10 TCID 50 per PCR reaction.