Will genome detection replace serology in blood screening for microbial agents?

Development and clinical validation of a one-step pentaplex real-time reverse transcription PCR assay for detection of hepatitis virus B, C, E, Treponema pallidum, and a human housekeeping gene

BACKGROUND

With the safety of blood transfusion being a major public health concern, the development of a rapid, sensitive, specific, and cost-effective multiplex PCR assay for simultaneous detection of hepatitis B virus(HBV), hepatitis C virus (HCV), hepatitis E virus (HEV), and Treponema pallidum(T. pallidum) in blood is crucial.

METHODS

Five primer pairs and probes were designed towards conserved regions of target genes and used to establish a one-step pentaplex real-time reverse transcription PCR(qRT-PCR) assay for simultaneous detection of HBV, HCV, HEV, T. pallidum, and RNase P(housekeeping gene), providing sample quality check. The clinical performance of the assay was further determined with 2400 blood samples from blood donors and patients in Zhejiang province, and compared the results with commercial singleplex qPCR and serological assays.

RESULTS

The 95% limit of detection(LOD) of HBV, HCV, HEV, and T. pallidum were 7.11 copies/µL, 7.65 copies/µL, 8.45 copies/µL, and 9.06 copies/µL, respectively. Moreover, the assay has good specificity and precision. Compared to the singleplex qPCR assay, the novel assay for detecting HBV, HCV, HEV, and T. pallidum presented 100% clinical sensitivity, specificity, and consistency. Several discrepant results between serological and pentaplex qRT-PCR assays were found. Of 2400 blood samples, there were 2(0.08%) HBsAg positive samples, 3(0.13%) anti-HCV positive samples, 29(1.21%) IgM anti-HEV positive samples and 6(0.25%) anti-T. pallidum positive samples proven negative in nucleic acid detection. 1(0.04%) HBV DNA positive sample and 1(0.04%) HEV RNA positive sample were detected negative by serological testing.

CONCLUSIONS

The developed pentaplex qRT-PCR is the first assay on simultaneous, sensitive, specific, and reproducible detection of HBV, HCV, HEV, T. pallidum, and RNase P in a single tube. It could detect pathogens in blood during the window period of infection and is a good tool for effectively screening blood donors and early clinical diagnosis.

Evaluation of serological transfusion-transmitted viral diseases and mutliplex nucleic acid testing in malaysian blood donors

BACKGROUND

Transmission of infectious diseases is a recognized complication of blood transfusion and blood products. Nucleic acid testing (NAT) may contribute to improved efficiency of blood screening and thereby increase the safety margin for transfused blood.

METHODS

Unscreened blood samples from 1388 randomized donors were selected for this study at the Transfusion Medicine Unit of Hospital Universiti Sains Malaysia (HUSM). Informed consent was obtained from all donors and blood samples were tested for HIV, HBV and HCV serologically and by NAT assay.

RESULTS

Of the 1,388 tested samples, 1,360 were non-reactive for both assays. Four samples (0.29%) were both serologically and NAT reactive. The remaining twenty-four samples were divided into two groups. Of these, five samples (0.366%) were NAT reactive and nineteen samples (1.37%) were serologically reactive. However, serology confirmation tests run on the latter nineteen samples were non-reactive.

CONCLUSIONS

Hence, NAT adds benefit of detecting "false positive" reactions via standard serology, the cost of administering NAT also need further consideration and study.

Design and development of an in-house multiplex RT-PCR assay for simultaneous detection of HIV-1 and HCV in plasma samples

BACKGROUND AND OBJECTIVES

HIV-1 and HCV infections are life threatening problems in patients who receive blood products. Serological methods have proven useful in detecting these infections, but there are setbacks that make it challenging to detect these infectious agents. By the advent of Nucleic Acid Testing (NAT) methods, especially in multiplex format, more precise detection is possible.

MATERIALS AND METHODS

We have developed a multiplex RT-PCR assay for simultaneous detection of HIV-1 and HCV. Primers were designed for highly conserved region of genome of each virus. Using these primers and standard plasmids, we determined the limit of detection, clinical and analytical specificity and sensitivity of the assay. Monoplex and multiplex RT-PCR were performed.

RESULTS

Analytical sensitivity was considered to be 100 and 200 copies/ml for HIV-1 and HCV, respectively. High concentration of one virus had no significant effect on the detection of the other one with low concentration. By analysis of 40 samples, clinical sensitivity of the assay was determined to be 97.5%. Using different viral and human genome samples, the specificity of the assay was evaluated to be 100%.

CONCLUSIONS

The aim of this study was to develop a reliable, rapid and cost effective method to detect HIV-1 and HCV simultaneously. Results showed that this simple and rapid method is perfectly capable of detecting two viruses in clinical samples.

Performance evaluation of the new fully automated human immunodeficiency virus antigen-antibody combination assay designed for blood screening

BACKGROUND

Before the introduction of human immunodeficiency virus (HIV) combination assays, serologic diagnosis of HIV infection was performed with assays that detected either antibodies or p24 antigen. Owing to the capability to detect the early appearance of p24 antigen, combination assays that are designed for simultaneous detection of antibodies and antigen can significantly reduce the diagnostic window.

STUDY DESIGN AND METHODS

Specificity and sensitivity of a commercially available HIV antigen-antibody combination assay (Abbott PRISM; assay is not licensed by the FDA for use in the United States) were evaluated in a multicenter study by testing volunteer blood donors, hospitalized patients, seroconversion panels, and p24 antigen and HIV antibody subtype panels. Performance data were compared to a commercially available HIV combination assay and the PRISM HIV O Plus assay.

RESULTS

Apparent specificity of 99.95 percent was observed in the donor population for the PRISM HIV antigen-antibody combination assay, and better seroconversion sensitivity was demonstrated compared with another combination assay and the PRISM HIV O Plus assay. Analytical HIV antigen detection sensitivity averaged 33 pg per mL on the Agence Française de Sécurité Sanitaire des Produits de Santé (AFSSAPS) panel. Furthermore, comparable antigen sensitivity was demonstrated for 32 HIV-1 group M subtype and group O panels. The PRISM HIV combination assay detected all HIV-1 group M and O and HIV-2 antibody-positive specimens evaluated.

CONCLUSIONS

The PRISM HIV antigen-antibody combination assay demonstrated a significant reduction of the window period for diagnosis of HIV infection. The assay demonstrated enhanced specificity and sensitivity along with broad subtype detection. The assay performance represents the "state-of-the art" technology for serologic blood screening of HIV infection.

Evaluation of processing characteristics of photochemically treated pooled platelets: target requirements for the INTERCEPT Blood System comply with routine use after process optimization

To ensure good performance of pathogen inactivation with the INTERCEPT blood system, specific target requirements must be met for platelet dose, volume, plasma content and residual red blood cells (RBCs) prior to photochemical treatment (PCT). A two-arm in vitro study was conducted to compare quality parameters of pooled platelet concentrates (PCs), either treated (test units) or nontreated (control units). PCs meeting European requirements were evaluated with reference to their compliance with INTERCEPT guard bands. Of 50 PCs (25 tests and 25 controls) meeting European quality requirements, 24% (three test and three controls units) did not reach INTERCEPT requirements, particularly in terms of sufficient volumes and RBC contamination. The buffy-coat optimization procedure assessed prior to this study ensured plasma contents well within target limits of 30 to 45%. Due to PCT-related in-process loss of 11% in volume (34.38 +/- 3.94) and in platelet dose (0.41 +/- 0.14), the mean platelet dose was significantly (P < 0.001) lower in test units: 3.1 +/- 0.3 versus 3.6 +/- 0.4 x 10(11). After treatment, six of the overall 25 test units (25%) would not have met the European guideline for platelet dose (3.0 x 10(11)). Before implementation of techniques for pathogen reduction, each centre should optimize processing steps during a validation procedure to ensure PC complying with INTERCEPT targets before and European targets after treatment. Besides buffy-coat optimization for sufficient plasma reduction, centrifugation profiles need to be optimized as well to prevent PC with low volumes and, in particular, with higher than acceptable RBC contamination.

Functional characteristics of buffy-coat PLTs photochemically treated with amotosalen-HCl for pathogen inactivation

BACKGROUND

One blood system for PLTs (INTERCEPT, Baxter Transfusion Therapies) is based on photochemical treatment (PCT) with small molecules that target cross-link nucleic acids (Helinx technology, Cerus Corp.) with amotosalen-HCl (S-59) and UVA light (320-400 nm) to inactivate pathogens and WBCs.

STUDY DESIGN AND METHODS

A two-arm in vitro study was conducted to compare pooled buffy-coat-derived PLT concentrates (PCs) treated with the INTERCEPT blood system, resuspended in PLT additive solution (PAS) III (InterSol, Baxter Transfusion Therapies), and stored for up to 7 days (test units, n = 20) with unpaired, nontreated PCs, resuspended in PAS II (T-Sol, Baxter Transfusion Therapies), and prepared at the same center in the same manner (control units, n = 18).

RESULTS

PLT dose (x 1011/unit +/- SD) on Day 1 immediately following PCT was 3.0 +/- 0.4 for test units and 3.2 +/- 0.4 for control units. After 7 days of storage, the pH of all test units was maintained above 6.8. No marked trend was observed in the hypotonic shock response (HSR). Values among study groups were similar at the end of observation period: 68 +/- 11 percent for control unites versus 67 +/- 8 percent for test units (p > 0.05). Aggregation response to ristocetin was slightly lower in test units: at Day 7, 65 +/- 10 percent versus 76 +/- 6 percent (p < 0.05). Significantly higher (p < 0.001) glucose consumption, lactate production, and CD62P expression were observed in test units.

CONCLUSION

Compared to nontreated PLTs, the PCT process was associated with a variety of differences of in vitro analyses. Although significant, these changes were relatively small in most cases. Characteristics correlated with survival in vivo such as HSR and swirling were comparable between both study groups, indicating that the viability of the majority of cells appears to have persisted throughout 7 days of storage. The impact of this finding, however, remains to be investigated in clinical trials performed with 7-day stored PLTs.

HCV viral load in anti-HCV-reactive donors and infectivity for their recipients

BACKGROUND

An attempt has been made to determine the minimum level of HCV nucleic acid in donors associated with infection of recipients. This is important for considerations about assay sensitivity, use of minipool versus single-donation testing, and continued use of serologic testing.

STUDY DESIGN AND METHODS

A total of 5387 specimens from the Transfusion-Transmitted Viruses Study in the 1970s were screened for antibody to HCV (anti-HCV). The outcome in recipients of seroreactive donations was examined for viremia and seroconversion. Present techniques for both groups included third-generation EIA, RIBA, quantitative RT-PCR assay, and transcription-mediated amplification (TMA) assay.

RESULTS

A total of 156 recipients of components from 180 anti-HCV-reactive donors were identified. One-hundred seven of these were HCV-naïve before transfusion and received a single, confirmed seropositive unit; 94 (88%) became infected. Eighty-five recipients had donors whose HCV RNA level was quantifiable by RT-PCR (range, 182-3,310,000 copies/mL). Eighty-three (98%) seroconverted. Of the remaining 22, a total of 10 received units positive for HCV RNA detected only by TMA; all 10 recipients seroconverted. Of the remaining 12 recipients of anti-HCV+, TMA-negative units, 1 recipient seroconverted.

CONCLUSIONS

High rates of transmission were seen at all levels of viremia, and one donor transmitted with undetectable levels in the TMA assay. Current HCV RNA testing will therefore not interdict all infectious units, even with single-donation testing, and serologic screening must be continued.

Impact of changes in viral marker screening assays

BACKGROUND

Monitoring the performance of routinely used infectious disease serologic tests is necessary to evaluate their effectiveness in identifying true-positive units and erroneously disqualifying safe blood donors.

METHODS

With two large screening test data sets collected between 1991 and 1998 and between 1997 and 2000, the impact of changes in screening assays for HIV, HCV, and HBsAg was analyzed with regard to the prevalence of confirmed-positive, indeterminate, and confirmed-negative results and the deferral of donors with an indeterminate or negative results (donor loss).

RESULTS

The prevalence of indeterminate results and donors loss increased significantly in the 6 months after introduction of an HIV-1/2 EIA. A second-generation HCV EIA increased the detection of confirmed-positive donations in repeat donors (p < 0.001) and increased the prevalence of indeterminate donations. Implementation of a third-generation HCV EIA resulted in a significant decrease in indeterminate results in first-time donors. Nonspecific test results increased when HBsAg test kits from a different manufacturer were introduced or different lots of HIV antibody screening test kits from the same manufacturer were used.

CONCLUSION

Introduction of newly licensed versions of assays, switching kit manufacturers, and lot-to-lot variations have an impact on rates of deferrals of safe donors as well as sensitivity of routine screening. Before considering changes in screening tests, blood centers should be aware of, and evaluate, the potential impact on donor loss.

Transfusion risks of yesterday and of today

The viral safety of the blood supply provided by serological tests alone decreased the residual risk of viral transmission to less than 1:250,000 for hepatitis C virus (HCV) and 1:1.3 M for HIV in the EU and the USA in 2000. This was further improved to 1:2-4 M by the introduction of nucleic acid testing (NAT) for HCV and HIV RNA that considerably reduced the risk of window period transmission. However, over the past 20 years, the successive introduction of up to 10 direct or surrogate viral markers enormously complicated the screening process and testing errors have become the main residual risk of viral transmission by transfusion. At over $ 2 M per QALY, the very low cost-effectiveness of NAT and some other tests overburdens limited funds that might be better used for other health care priorities. At the same time, haemovigilance programmes have shown that blood transfused to the wrong patient and a range of immunological consequences of transfusion caused two deaths per million transfusions and little is done to prevent them. There are means of limiting these serious hazards of transfusion that should become the priority in blood safety.

Highly sensitive multiplex assay for detection of human immunodeficiency virus type 1 and hepatitis C virus RNA

Various nucleic acid assays have been developed and implemented for diagnostics and therapeutic monitoring of human immunodeficiency virus type 1 (HIV-1) and hepatitis C virus (HCV) infections. The high-throughput, semiautomated assays described here were developed to provide a method suitable for screening plasma specimens for the presence of HIV-1 and HCV RNAs. Three assays were developed: a multiplex HIV-1/HCV assay for simultaneous detection of HIV-1 and HCV, and discriminatory assays for specific detection of HIV-1 and HCV. The assay systems utilize three proprietary technologies: (i) target capture-based sample preparation, (ii) transcription-mediated amplification (TMA), and (iii) hybridization protection assay (HPA). An internal control is incorporated into each reaction to control for every step of the assay and identify random false-negative reactions. The assays demonstrated a sensitivity of at least 100 copies/ml for each target, and they detected with similar sensitivity all major variants of HCV and HIV-1, including HIV-1 group O strains. Assay sensitivity for one virus was not affected by the presence of the other. The specificity of these TMA-driven assays was >or=99.5% in both normal donor specimens and plasma containing potentially interfering substances or other blood-borne pathogens. Statistical receiver operating characteristic plots of 1 - specificity versus sensitivity data determined very wide analyte cutoff values for each assay at the point at which the assay specificity and sensitivity were both >or=99.5%. The sensitivity, specificity, and throughput capability predict that these assays will be valuable for large-volume plasma screening, either in a blood bank setting or in other diagnostic applications.

Significant closure of the human immunodeficiency virus type 1 and hepatitis C virus preseroconversion detection windows with a transcription-mediated-amplification-driven assay

While the present generation of serology-based assays has significantly decreased the number of human immunodeficiency virus type 1 (HIV-1) and hepatitis C virus (HCV) infections acquired by transfusion, the possibility of infected donations escaping detection still exists. The average seronegative viremic window duration during which immunological assays are unable to detect the virus is estimated to be between 16 and 22 days for HIV-1 and approximately 70 days for HCV. Significant reduction of detection window duration was demonstrated using a nucleic acid amplification assay, the Procleix HIV-1/HCV Assay, which utilizes transcription-mediated amplification technology to simultaneously detect HIV-1 and HCV RNAs. For 26 commercially available HIV-1 seroconversion panels tested, specimens were reactive in the HIV-1/HCV assay at the same time as or earlier than in serological assays. Overall, the HIV-1/HCV assay was able to reduce the detection window duration by an average of 14 days and 6 days compared to tests relying on recognition of HIV-1 antibody and p24 antigen, respectively. For 24 commercially available HCV seroconversion panels tested, the specimens were reactive in the HIV-1/HCV assay at an earlier blood sampling date than in serological assays, reducing the detection window duration by an average of 26 days. Similar results were obtained in testing the HIV-1 and HCV seroconversion panels in the virus-specific HIV-1- and HCV-discriminatory assays, respectively. In conclusion, the HIV-1/HCV assay and corresponding discriminatory assays significantly reduced detection window durations compared to immunoassays.

Sensitive detection of genetic variants of HIV-1 and HCV with an HIV-1/HCV assay based on transcription-mediated amplification

This paper describes a comprehensive study of hepatitis C virus (HCV) and human immunodeficiency virus type 1 (HIV-1) genotype sensitivity of the transcription-mediated amplification (TMA)-based HIV-1/HCV assay, developed and manufactured by Gen-Probe Incorporated (San Diego, CA) for screening human plasma specimens in blood bank settings. The TMA HIV-1/HCV assay is a qualitative, in vitro nucleic acid testing system used for initial screening. HIV-1 and HCV discriminatory assays are used to distinguish between HIV-1 and HCV infection or co-infection. In this study, multiple unique specimens representing HCV genotypes 1-6 were tested at various dilutions. The results show that the TMA HIV-1/HCV assay and the TMA HCV discriminatory assay have similar HCV genotype sensitivity, as both assays detected all six genotypes at 100 copies/ml and nearly all replicates tested at 30 copies/ml. Similarly, numerous unique specimens representing HIV-1 group M subtypes (A-G), HIV-1 group N, and group O specimens were tested at various dilutions. The TMA HIV-1/HCV assay and the TMA HIV-1 discriminatory assay were found to have similar HIV-1 subtype sensitivity; all variants at 100 copies/ml and nearly all at 30 copies/ml were detected. These results indicate that the TMA assays meet the sensitivity requirements for blood screening in blood banks worldwide.