Screening the blood supply for West Nile virus RNA by nucleic acid amplification testing.

BACKGROUND: The use of nucleic acid amplification tests of "minipools" of 16 samples to screen blood donors for West Nile virus RNA began in July 2003. We report the yield and characteristics of positive donations and the incremental yield and safety of nucleic acid amplification tests of individual donations. METHODS: Reactive minipools were analyzed to identify the individual reactive donations. For the regions with the highest yield on minipool testing, retrospective nucleic acid amplification testing was performed on individual donations that were negative on minipool testing. Reactive donations were confirmed by alternative nucleic acid amplification tests and IgM and IgG tests, and donors were followed to document seroconversion. RESULTS: From July 1 through October 31, 2003, 677,603 donations were prospectively screened for West Nile virus by minipool testing, yielding 183 confirmed viremic donations (0.027 percent, or 1 in 3703 donations). Retrospective individual testing of 23,088 donations from high-prevalence regions that were negative on minipool testing yielded 30 additional units with a low level of viremia, with 14 additional viremic units detected by prospective testing of individual donations late in the 2003 transmission season. Of all the viremic units detected, 5 percent were detected only by individual testing and were negative for IgM antibody, 29 percent were detected by individual testing after IgM seroconversion, and 66 percent were detected by minipool testing. West Nile virus infection was confirmed in both recipients of IgM-negative units that were reactive on individual testing, whereas neither recipient of antibody-positive blood components that were reactive on individual testing was infected. In 2004, prospective testing of individual donations in regions that yielded donations that were reactive on minipool testing resulted in a 32 percent incremental yield of units with a low level of viremia that would have been missed by minipool testing. CONCLUSIONS: Although nucleic acid amplification testing of minipools of blood donations prevented hundreds of cases of West Nile virus infection in 2003, it failed to detect units with a low level of viremia, some of which were antibody-negative and infectious. These data support the use of targeted nucleic acid amplification testing of individual donations in high-prevalence regions, a strategy that was implemented successfully in 2004.

Clinical significance of nondiscriminated reactive results with the Chiron Procleix HIV-1 and HCV assay.

BACKGROUND: A NAT was developed (Procleix multiplex, Chiron Corporation) to simultaneously detect HIV-1 and HCV RNA with multiplex transcription-mediated amplification (mTMA) on pooled or single donations. HIV-1 and/or HCV RNA discriminatory probes confirm infection and discriminate the virus type. When a multiplex reactive sample does not react in discriminatory assays, the result is considered nondiscriminated reactive (NDR) and the donor status is uncertain. This study was designed to determine the clinical significance of NDR results. STUDY DESIGN AND METHODS: Three years of donor NAT and serology results were reviewed to determine HCV and HIV-1 infection rates as well as NDR events. Index NDR and seronegative donations were retested by mTMA and serology. Follow-up samples were tested by serology, mTMA, and PCR (selected samples). RESULTS: From April 1999 through April 2002, 5.1 million donations were screened with Procleix HIV-1 and HCV mTMA. The observed NDR rate declined from 0.014 percent (1 in 7242) to 0.0053 percent (1 in 18,795). None of the 462 donors with index NDR donations and additional NAT and serology data (from 724 donation and follow-up samples) were found infected. CONCLUSION: In most NDRs, the original mTMA reactivity is not reproducible and likely related to technical errors (mTMA cross-contamination). The retest and clinical follow-up data, combined with published evidence that the two discriminatory assays have the same sensitivity as multiplex HIV-1 and HCV, support the recommendation that donors with an NDR result for whom the multiplex reactivity cannot be reproduced should either not be notified or be deferred or should be counseled that they are not infected and expeditiously reinstated.