Trends in residual risk of transfusion-transmitted viral infections in France between 1992 and 2000

[Trends in residual risk of transfusion-transmitted viral infections (HIV, HCV, HBV) in France between 1992 and 2002 and impact of viral genome screening (Nucleic Acid Testing)]

BACKGROUND

Monitoring trends in residual risk of transfusion-transmitted viral infections is important to assess improvements in blood safety. These trends were analysed over nine overlapping periods of 3 years from 1992 to 2002. The 2000-2002 estimates were compared to the results of HIV-1 and HCV NAT implemented on all blood donations in July 2001.

METHOD

As risk is mainly associated with the window period, residual risks were estimated by multiplying incidence rates by the durations of the window periods. For the first seven periods, incidence rates were calculated from data collected by the blood centres belonging to the Transfusion-Transmissible Agents Working Group which collect more than 50% of blood donations in France, and for the two last periods, on the overall blood supply.

RESULTS

On the 2000-2002 period, residual risks without NAT were estimated at 1 in 1,400,000 for HIV, at 1 in 1,000,000 for HCV and at 1 in 400,000 for HBV. With minipool NAT, the residual risk become nearly two times lower for HIV (1 in 2.5 million donations) and seven times lower for HCV (1 in 6.65 million donations). For HIV, of the 4.9 million donations screened with NAT between July 2001 and June 2003, two were remote thanks to the NAT, which is consistent with the NAT expected yield. Concerning HCV, one out of the four WP predicted cases was detected with NAT. Without NAT, the overall residual risk for the three viruses combined (HIV, HCV, HBV) decreased from 1 in 65,000 to 1 in 235,000 donations between 1992 and 2002. Since the implementation of NAT, the current overall residual risk is 1 in 325,000 donations (28% less than without NAT).

CONCLUSION

NAT results confirm the validity of residual risk estimates given by the model, and the limited benefit of genomic screening due to the very low level of residual risk at the time of its implementation.

Transfusion-transmitted hepatitis E caused by apparently indigenous hepatitis E virus strain in Hokkaido, Japan

BACKGROUND

In industrialized countries, sporadic cases of hepatitis E have been reported in individuals who have never been in an endemic area. Hepatitis E virus (HEV) infection commonly occurs via the fecal-oral route but a potential risk of transfusion transmission route has been suggested.

STUDY DESIGN AND METHODS

A 67-year-old Japanese male patient who had never been abroad received a transfusion of blood from 23 voluntary donors and developed acute hepatitis with unknown etiology after transfusion. His blood samples were tested for viral markers of hepatitis viruses.

RESULTS

HAV, HBV, HCV, CMV, and EBV were ruled out as causative agents in this case. The patient's blood sample in the acute phase contained HEV RNA as well as IgM and IgG anti-HEV. HEV RNA was also detected in one of the FFP units transfused. The donor had no history of traveling abroad and had a normal ALT level at the time of donation. The PCR products from the patient and the donor showed complete identity for two distinct regions of HEV within open reading frame 1.

CONCLUSION

The patient was infected with HEV via transfused blood from a volunteer donor. A potential risk of posttransfusion hepatitis E should be considered even in nonendemic countries.

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.

Combination HCV core antigen and antibody assay on a fully automated chemiluminescence analyzer

BACKGROUND

HCV exposure among blood donors is serologically determined by detection of antibodies to HCV (anti-HCV); however, the recent development of an assay for the detection of HCV core antigen identifies infection before anti-HCV development. Simultaneous detection of HCV core antigen and anti-HCV would shorten the window period before seroconversion over conventional HCV antibody screening assays.

STUDY DESIGN AND METHODS

A prototype chemiluminescent immunoassay was developed for simultaneous detection of HCV core antigen and anti-HCV in human sera and plasma. The assay was performed on a single-channel instrument representing an automated serologic analyzer (PRISM, Abbott Laboratories) system. Sensitivity and specificity were evaluated by testing 23 HCV seroconversion panels and plasma or sera from volunteer blood donors.

RESULTS

The prototype HCV core antigen and antibody combination assay detected 80 of 89 (89.9% ) HCV RNA-positive and antibody-negative specimens from 23 panels, thereby reducing the seroconversion window period by an average of 34.3 days compared to PRISM HCV antibody detection. All PRISM HCV antibody-positive specimens were detected by the combination assay for a relative sensitivity of 100 percent. The repeatedly reactive rate was 0.20 percent based on testing of 3017 screened anti-HCV-negative sera and plasma.

CONCLUSIONS

The prototype combination assay was shown to detect HCV core antigen and anti-HCV simultaneously and significantly closed the time gap between the initial detection of HCV RNA and the first appearance of detectable antibodies to HCV.

[Application of molecular biology to blood transfusion safety: the nucleic acid testing]

Nucleic Acid Testing (NAT) for HIV-1 and HCV has been introduced in France and became mandatory for all homologous blood donations since July 1st 2001 in addition to serology screening. Previously, a feasibility study led to the selection of 2 technologies : a TMA based assay (Chiron) uses the Procleix HIV-/HCV assay on pools of 8 samples and a PCR based assay from BioMérieux-Roche which is a combination of an RNA extraction system (NucliSens, BioMérieux) with a fully automated system for nucleic acid amplification and detection (Cobas Amplicor, Roche). This system uses the Cobas Ampliscreen HCV test v.2.0 and the The Cobas Ampliscreen HIV test v1.5, on 24 sample pools. Pooling was required because single-donation testing is not yet feasible, as a result of the limitations in automation available for all current NAT technologies. The two technologies were easily implemented and showed nearly the same detection limit for HCV RNA and HIV-1 RNA. During a one-year period, from July 1st 2001 to June 30, 2002, out of the 2.5 million donations tested, the NAT yield resulted in one HIV-1 RNA positive-antibody negative donation and one HCV RNA positive-antibody negative donation. Two HIV NAT positive-antibody negative donations were missed by minipool NAT because a very low viral load. Moreover, the NAT implementation did not impact on blood component availability, including platelet concentrates.

[Prevalence of HBV, HCV, HIV and HTLV in autologous blood donors in France between 1993 and 2000]

The epidemiological surveillance of autologous blood donors has been carried out in France since 1993. The number of autologous donors increased regularly from 1993 to 1997 but has decreased during the last three years to become less than 50,000 in 2000. The sex-ratio was stable over time (0.85 male for 1 female). The population of autologous donors grew older between 1993 and 2000: the proportion of those aged under 50 years old decreased from 29% in 1993 to 18% in 2000 while the proportion of those over 69 increased from 22 to 34%. Between 1993 and 2000, HbsAg prevalence decreased by a factor of 2.5 and HCV prevalence by a factor of 5. For HIV, a slight decrease was observed and the prevalence of HTLV was stable over time. In 2000, HCV prevalence (0.23%) was two times higher than HBsAg prevalence (0.12%), fifteen times higher than HTLV prevalence in Continental France (0.015%) and one hundred times higher than HIV prevalence (0.002%). The prevalence was similar in men and women for HCV, about two times higher in men than in women for HBsAg and three times higher for HIV. On the contrary, HTLV prevalence was about two times higher in women than in men. HBsAg and HCV prevalence rates were also calculated by age group. The prevalence rates for HBsAg increased up to the 30-39 age group among women and the 40-49 age group among men; then the rates decreased but were higher in men than in women. For HCV, while the prevalence increased continuously with age among women, a peak was reached for men in the 30-39 age group followed by a decrease up to the 50-59 age group and the prevalence was stable afterwards. The very low level of the current risk of transmitting viral infections by homologous transfusion and technical changes in autologous transfusion seem to be the two main factors that contributed to the recent decline in the number of autologous donors. The decrease in HBsAg and anti-HCV prevalence between 1993 and 2000 is multifactorial, but the drop observed for HCV is probably linked to a decrease in HCV prevalence of the general population over the last ten years.