Comparison of the analytical and operational performance of two viral nucleic acid test blood screening systems: Procleix Tigris and cobas s 201.

BACKGROUND: The operational and analytical performance of two automated triplex hepatitis B virus (HBV), hepatitis C virus (HCV), and human immunodeficiency virus (HIV) nucleic acid test (NAT) systems were compared in four screening laboratories of the French Blood Service. STUDY DESIGN AND METHODS: Two laboratories evaluated the Procleix Tigris system (Chiron/Gen-Probe) in individual donation (ID) format and two sites used the cobas s 201 system (Roche Molecular Systems) on minipools (MPs) of six donations. The analytical sensitivity, the specificity, and operational performance were compared. RESULTS: The ID to MP-NAT relative sensitivity factors in standard dilution panels of different genotypes varied between 8.7 and 21.9 for HCV RNA, 6.7 and 14.8 for HIV RNA, and 0.71 and 11.6 for HBV DNA. Tigris was 800-fold more sensitive than cobas s 201 (1:6) for a HIV group O sample, but did not detect the HIV-2 sample picked up by cobas s 201 with equal sensitivity as the HIV-1 group M samples. The specificity of both NAT systems after initial screening of 10,520 donations with Tigris and 1444 test pools on s 201 was 99.9 percent for both systems, but reached 100 percent after the repeat and pool resolution test algorithms. A higher throughput of the pool test protocol on cobas s 201 became apparent when the daily workload was more than 400 donations. CONCLUSIONS: Tigris ID-NAT format was significantly more sensitive than cobas s 201 MP-NAT in detecting HCV RNA and HIV RNA dilution panels, but despite the 1:6 dilution factor in s 201 the difference in sensitivity was not significant for some of the HBV genotype panels. Both NAT systems demonstrated acceptable operational performance, but for routine use further improvement in system reliability is desirable.

Sensitivity of two hepatitis B virus, hepatitis C virus (HCV), and human immunodeficiency virus (HIV) nucleic acid test systems relative to hepatitis B surface antigen, anti-HCV, anti-HIV, and p24/anti-HIV combination assays in seroconversion panels.

BACKGROUND: Accurate determination of the infectious window period (IWP) that remains with individual-donation (ID) or minipool (MP) NAT compared to those with serology assays is essential for residual risk estimations. STUDY DESIGN AND METHODS: The relative sensitivity of the Procleix Tigris system (Gen-Probe/Chiron) used in ID-NAT format and cobas s 201 (Roche Molecular Systems) applied in 1:6 diluted samples to mimic six-minipool (MP6) nucleic acid test (NAT) was assessed by quadruplicate testing of five seroconversion panels per marker. A mathematical analysis based on the log-linear increase of viremia in the ramp-up phase, as established with bDNA 3.0 assays enabled estimation of the IWP for human immunodeficiency virus (HIV) and hepatitis B virus (HBV) assays. RESULTS: The mean IWPs were Tigris HIV RNA 5.5 days, s 201 (1:6) HIV RNA 7.4 days, GenScreen Plus p24/anti-HIV 17.8 days, PRISM anti-HIV 19.0 days, Tigris HBV DNA 20.6 days, s 201 (1:6) HBV DNA 22.6 days, Bio-Rad hepatitis B surface antigen (HBsAg) 37.8 days, and PRISM HBsAg 35.5 days. At estimated 50 percent NAT seroconversion rates, s 201 (1:6) and Tigris showed mean window-period reduction times (WPRTs) of 30.5 to 35.5 days to hepatitis C virus antibody (anti-HCV) assays, 10.4 to 13.5 days to anti-HIV, or combination p24/anti-HIV assays and 12.8 to 17.2 days to HBsAg assays. CONCLUSIONS: Tigris ID-NAT detected HIV RNA 2 days earlier than s 201 MP6-NAT, but the difference in sensitivity between the two NAT systems was not significant in HBV seroconversion panels. Insufficient seroconversion samples were available for reliable modeling of WPRT in early HCV infection, but 1.4 to 2.0 days could be predicted by translating analytical sensitivity data. Both multiplex NAT systems demonstrate significant WPRTs compared to (combined) antigen and antibody assays.

Evaluation of the enhanced bacterial detection system for screening of contaminated platelets.

BACKGROUND: The Pall third-generation enhanced bacterial detection system (eBDS) was recently approved for detection of bacterial contamination in leukoreduced platelets (PLTs). The method is based on the measurement of the oxygen content as a marker for bacteria. eBDS incorporates major modifications including removal of the sample-set filter, modification of the culture medium, and incubation with agitation of the sample pouch. STUDY DESIGN AND METHODS: Ten whole blood-derived random-donor PLT units collected on Day 1 after donation and 10 single-donor apheresis PLT units were spiked with low levels of bacteria in three different blood transfusion centers. Inoculation was performed at a final concentration of 5 to 50 colony-forming units per mL with reference strains of five organisms involved in severe transfusion-associated infections. PLT units were stored at 22 degrees C for 24 hours before sampling. Six sample sets were then sterile-connected to each unit and placed on a horizontal agitator at 35 degrees C for 18 or 24 hours of incubation. RESULTS: No false-positive results were obtained, indicating a 100 percent specificity of the assay. Of 126 spiked sample pouches tested, 61 of 63 (96.82%) and 63 of 63 (100%) were detected positive after 18 or 24 hours of incubation, respectively. In the two missed cases that failed to detect Bacillus cereus, the measured oxygen was slightly above the detection threshold but was markedly different from the negative samples. CONCLUSION: The eBDS method allows definitive testing of PLTs as soon as 42 hours after collection and offers an alternative culture method to the BacT/ALERT system.

Is an assay for simultaneous detection of hepatitis C virus core antigen and antibody a valuable alternative to nucleic acid testing?

BACKGROUND: A new enzyme immunoassay based on the simultaneous detection of nucleocapsid proteins of hepatitis C virus (HCV) and anti-HCV (Monolisa HCV antigen-antibody Ultra, Bio-Rad) was evaluated as an alternative to nucleic acid testing (NAT) for the diagnosis of HCV infection during the window period in blood donations. STUDY DESIGN AND METHODS: The study included 107 sequential samples from 10 HCV seroconversion commercial panels; 81 samples were in the preseroconversion phase, and 26 were collected after seroconversion. All samples were tested with HCV antigen-antibody assay and the two minipool (MP) NAT procedures that are routinely used in France (transcription-mediated amplification in pools of 8 and COBAS AmpliScreen HCV test [Roche Diagnostic] in pools of 24 donations). RESULTS: From the 44 samples collected during window period that were MP-NAT-positive, 31 (70.5%) were also positive with the Monolisa HCV antigen-antibody assay. The mean delay in detecting HCV infection between these two methods was 5.1 days (range, 0-24 days). The Monolisa HCV antigen-antibody assay led to a reduction in the window period of 26.8 days (range, 0-72 days). All samples collected after seroconversion were detected with the HCV antigen-antibody assay. The specificity analyzed in 2503 consecutive blood donations was estimated at 99.88 percent. CONCLUSION: This new developed assay presents an improvement for the detection of HCV infection, especially in the early phase of infection when antibodies are undetectable. Although less sensitive than NAT, this assay could be a suitable solution for blood screening in developing countries where NAT (or HCV core antigen-specific assay) is not affordable or its implementation is not feasible.

HIV antibody screening remains indispensable for ensuring viral safety of blood components despite NAT implementation.

BACKGROUND: The main objective of the implementation of NAT for the screening of blood-borne viruses was to compensate for the failure of serologic assays during the window period. Because this new screening procedure theoretically covers the entire period of infectivity, the necessity for maintaining serologic assays in blood screening strategy could become questionable. STUDY DESIGN AND METHODS: To investigate this issue, a panel of 35 samples has been studied by NAT. These samples had been collected from HIV-1 antibody-positive individuals presenting a persistently low viral RNA load (<400 copies/mL) in the absence of antiviral therapy. All samples were analyzed with the minipool (x8) NAT routinely used in blood bank setting (HIV-1 and HCV assay based on transcription-mediated amplification) and with single-donation testing. RESULTS: The minipool NAT failed to detect the presence of HIV RNA in 15 of the 35 samples (11 remained negative when retested). Single-donation testing gave negative results in 4 samples (3 remained negative when retested). Fourteen of the 18 samples with a viral load greater than 50 copies per mL were positive by minipool NAT versus 6 of the 17 samples with fewer than 50 copies per mL (p = 0.02). CONCLUSION: The results clearly demonstrate that anti-HIV screening should not be withdrawn from biologic qualification procedures of blood donations, even when single NAT is performed.