Revised nucleic acid test window periods: Applications and limitations in organ donation practice

BACKGROUND

Nucleic acid test window periods for HIV, HCV, and HBV facilitate estimation of the residual risk of unexpected disease transmission and assist clinicians in determining the timeframe in which a recently acquired infection is at risk of nondetection.

OBJECTIVES

Firstly, to provide revised estimates of the NAT window periods based on a currently used triplex NAT assay. Secondly, to examine their validity in organ donation and transplantation practice.

METHOD

Estimates were based on the Procleix Ultrio Elite Assay (Grifols Diagnostic Solutions Inc. California, USA). The manufacturer's X50 and X95 limits of detection (LOD) were utilised. Viral doubling times of 0.85, 0.45, and 2.56 days and conversion factors for IU per ml to copies per mL of 0.6, 3.4, and 5 were assumed for HIV, HCV, and HBV respectively. Window periods were derived from the X50 and X95 LODs, based on a range of potential inoculum volumes.

RESULTS

Calculated X50 window periods were 5.1 (4.5-5.8), 2.7 (2.4-2.9), and 16.6 (14.2-19.1) days for HIV, HCV, and HBV respectively. Calculated X50 window periods, based on whole body plasma volume, were 11.8 (10.3-13.3), 6.2 (5.6-6.8) and 36.7 (31.3-42.1) days respectively.

CONCLUSION

X50 NAT window periods were significantly shorter for HBV and HCV and sit at the lower range of previously published estimates for HIV .  Current modeling assumptions may not account for all unexpected transmission events and may no longer be suitable for application to organ donation and transplantation.

Is dual testing for hepatitis C necessary? Modelling the risk of removing hepatitis C antibody testing for Australian blood donations

BACKGROUND AND OBJECTIVES

Parallel testing of blood donations for hepatitis C virus (HCV) antibody and HCV RNA by nucleic acid testing (NAT) has been standard practice in Australia since 2000. Meanwhile, NAT technologies have improved, and HCV has become a curable disease. This has resulted in a significant reduction in the risk and clinical consequences of HCV transmission through transfusion. This study aimed to estimate the residual risk (RR) under various testing options to determine the optimal testing strategy.

MATERIALS AND METHODS

A developed deterministic model calculated the RR of HCV transmission for four testing strategies. A low, mid and high estimate of the RR was calculated for each. The testing strategies modelled were as follows: universal dual testing, targeted dual testing for higher risk groups (first-time donors or transfusible component donations) and universal NAT only.

RESULTS

The mid estimate of the RR was 1 in 151 million for universal dual testing, 1 in 111 million for targeted dual testing of first-time donors, 1 in 151 million for targeted dual testing for transfusible component donations and 1 in 66 million for universal NAT only. For all testing strategies, all estimates were considerably less than 1 in 1 million.

CONCLUSION

Antibody testing in addition to NAT does not materially change the risk profile. Even conservative estimates for the cessation of anti-HCV predict an HCV transmission risk substantially below 1 in 1 million. Therefore, given that it is not contributing to blood safety in Australia but consuming resources, anti-HCV testing can safely be discontinued.

Blood donation amongst people who inject drugs in Australia: research supporting policy change

BACKGROUND AND OBJECTIVES

Until recently, people in Australia with a history of injection drug use (IDU) were deferred indefinitely from donating blood. Knowledge gaps regarding policy non-compliance and the prevalence of blood donation practices amongst people who inject drugs (PWID) precluded changes to this policy. We sought to address these gaps and to estimate the additional risk to Australia's blood supply associated with changing the indefinite deferral policy to 1 or 5 years since last injecting episode.

MATERIALS AND METHODS

Data on blood donation amongst PWID were collected from 1853 interviews across two Australian studies of PWID conducted during 2015/16. Mathematical modelling was used to estimate the additional risk of hepatitis C (HCV)-infected window period collections as a result of changing the deferral policy.

RESULTS

A very few (2-4%) study participants reported ever donating blood after ≥1 IDU episode. Changing the deferral policy from indefinite to 1 or 5 years was estimated to result in an additional 0·00000070 (95%CI: 0·00000033-0·00000165) or 0·00000020 (95%CI: 0·00000008-0·00000041) HCV-positive window period collections per year, respectively.

CONCLUSION

Changing Australia's indefinite deferral period to 1 or 5 years since last injecting episode poses a negligible increase in the risk of HCV-infected window period collections from blood donors with a history of IDU. Our results informed a successful submission to the Australian regulator to change the deferral period from indefinite to 5 years since last injecting episode, a policy which came into effect in September 2018.

Modelling the risk of transfusion-transmitted syphilis: a reconsideration of blood donation testing strategies

BACKGROUND AND OBJECTIVES

Donor syphilis testing began in the 1940s amidst widespread transfusion-transmitted syphilis (TTS). Since then, the introduction of penicillin, pre-donation screening questionnaires and improved storage conditions have contributed to reducing transmission risk. Consequently, universal testing may no longer be cost-effective. This study analysed alternative options for donor syphilis testing to determine the optimal strategy.

MATERIALS AND METHODS

A model was developed using conservative parameter estimates for factors affecting TTS and 2009-2015 Australian donations to calculate risk outcomes (TTS infections, tertiary syphilis in recipients and transfusion-associated congenital syphilis) and cost-effectiveness of alternative testing strategies. The strategies modelled were as follows: universal testing, targeted-testing of high-risk groups (males ≤50 years old and first-time donors) and no testing.

RESULTS

The estimated risk of TTS is one in 49·5 million transfusions for universal testing, one in 6 million for targeted-testing of males ≤50 years old, one in 4 million for targeted-testing of first-time donors and one in 2·8 million for no testing. For all strategies, the risk of tertiary and congenital syphilis is <1 in 100 million. Universal testing is the least cost-effective strategy with an incremental cost-effectiveness ratio (ICER) estimated at $538·5 million per disability-adjusted life year averted.

CONCLUSION

Universal testing is not required to maintain the risk of TTS within tolerable limits and is estimated to greatly exceed acceptable ICERs for blood safety interventions. However, despite a strong economic and risk-based rationale, given the epidemiology of syphilis in Australia is changing, feedback from critical stakeholders is not currently supportive of reducing testing.

Re-examining blood donor deferral criteria relating to injecting drug use

BACKGROUND AND AIMS

Potential Australian blood donors are deferred indefinitely if they report a history of injecting drug use (IDU), or for 12 months if they report having engaged in sexual activity with someone who might have ever injected. Given incremental improvements in blood safety, this study sought to examine whether Australia's IDU-related eligibility criteria reflected current scientific evidence, were consistent with international best practice and, if current IDU-related policies were to be changed, how this should happen.

METHODS

An expert committee was formed to review relevant literature with a focus on issues including: the epidemiology of IDU in Australia and key transfusion-transmissible infections (TTIs) among Australian people who inject drugs (PWID); and, 'non-compliance' among PWID regarding IDU-related blood donation guidelines. International policies relating to blood donation and IDU were also reviewed. Modelling with available data estimated the risk of TTIs remaining undetected if the Blood Service's IDU-related guidelines were changed.

RESULTS

Very few (<1%) Australians engage in IDU, and IDU risk practices are reported by only a minority of PWID. However, the prevalence of HCV remains high among PWID, and IDU remains a key transmission route for various TTIs. Insufficient data were available to inform appropriate estimates of cessation and relapse among Australian PWID. Modelling findings indicated that the risk of not detecting HIV becomes greater than the reference group at a threshold of non-admission of being an active PWID of around 1.8% (0.5-5.1%). Excluding Japan, all Organisation for the Economic Co-operation and Development member countries permanently exclude individuals with a history of IDU from donating.

CONCLUSION

Numerous research gaps meant that the study's expert Review Committee was unable to recommend altering Australia's current IDU-related blood donation guidelines. However, having identified critical knowledge gaps and future areas of research, the review made important steps toward changing the criteria.

Seroprevalence of Antibodies to Ross River and Barmah Forest Viruses: Possible Implications for Blood Transfusion Safety After Extreme Weather Events

Climate change is predicted to increase the transmission of many vector-borne pathogens, representing an increasing threat to a safe blood supply. In early 2011, Australia experienced catastrophic rainfall and flooding, coupled with increased arbovirus transmission. We used Ross River (RRV) and Barmah Forest (BFV) viruses as test cases to investigate the potential risk posed to Australia's blood supply after this period of increased rainfall . We estimated the risk of collecting an infected donation as one in 2,500-58,000 for RRV and one in 2,000-28,000 for BFV. Climate change may incrementally increase the arbovirus threat to blood safety.

Comparison of the risk of viral infection between the living and nonliving musculoskeletal tissue donors in Australia

Screening of musculoskeletal tissue donors with nucleic acid testing (NAT) for human immunodeficiency virus (HIV) and hepatitis C virus (HCV) has been implemented in the United States and other developed nations. However, in contrast to the donor demographics in the United States, the majority of Australian musculoskeletal tissue donations are primarily from living surgical donors. The objective of our study was to determine and compare the risk of viral infection associated with musculoskeletal tissue donation from living and nonliving donors in Australia. We studied serum samples from 12 415 consecutive musculoskeletal tissue donors between 1993 and 2004. This included 10 937 surgical donations, and 1478 donations obtained from postmortem organ donation patients and cadaveric donors. Current mandatory retesting of surgical donors 6 months postdonation reduces the risk of viral infection by approximately 95% by eliminating almost all donors in the window period. The addition of nucleic acid amplification testing for nonliving donors would similarly reduce the window period, and consequently the residual risk by approximately 50% for hepatitis B virus, 55% for HIV, and 90% for HCV. NAT, using appropriately validated assays for nonliving donors, would reduce the residual risk to levels comparable to that in living donors (where the 95% reduction for quarantining pending the 180-day re-test is included).

The risk of HIV, HBV, HCV and HTLV infection among musculoskeletal tissue donors in Australia

In Australia, there are no current national estimates of the risks of transmission of human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV) or human T-lymphotrophic virus (HTLV) by musculoskeletal tissue transplantation. We determined the prevalence rates of antibodies against HIV (anti-HIV), HCV (anti-HCV) and HTLV (anti-HTLV) and Hepatitis B surface antigen (HBsAg) for 12,415 musculoskeletal tissue donors from three major bone tissue banks across Australia for the period 1993-2004. The prevalence (per 100,000 persons) was 64.44 for anti-HIV, 407.13 for HBsAg, 534.63 for anti-HCV and 121.88 for anti-HTLV. The estimated probability of viremia at the time of donation was 1 in 128,000, 1 in 189,000, 1 in 55,000 and 1 in 118,000, respectively. With the addition of nucleic acid amplification testing (NAT), the probability of donor viremia would be reduced to 1 in 315,000 for HIV, 1 in 385,000 for HBV and 1 in 500,000 for HCV. The prevalence of HIV, HBV, HCV and HTLV although low, are higher among musculoskeletal tissue donors than among first-time blood donors. The risks associated with musculoskeletal donation will be reduced with NAT, though further cost analysis is required prior to its implementation.

Geographical distribution of hepatitis C virus genotypes in blood donors: an international collaborative survey

The frequency of infection with the six classified major genotypes of hepatitis C virus (HCV) was investigated in 447 infected volunteer blood donors from the following nine countries: Scotland, Finland, The Netherlands, Hungary, Australia, Egypt, Japan, Hong Kong, and Taiwan. Viral sequences in plasma from blood donors infected with HCV were amplified in the 5'-noncoding region and were typed by restriction fragment length polymorphism analysis. Electrophoresis of DNA fragments produced by cleavage with HaeIII-RsaI and ScrFI-HinfI allowed HCV types 1 (or 5), 2, 3, 4, and 6 to be identified. Further analysis with MvaI-HinfI allowed sequences of the type 5 genotype to be distinguished from sequences of the type 1 genotype. Types 1, 2, and 3 accounted for almost all infections in donors from Scotland, Finland, The Netherlands, and Australia. Types 2 and 3 were not found in the eastern European country (Hungary), where all but one of the donors were infected with type 1. Donors from Japan and Taiwan were infected only with type 1 or 2, while types 1, 2, and 6 were found in those from Hong Kong. HCV infection among Egyptians was almost always by type 4. Donors infected with HCV type 1 showed broad serological reactivity with all four antigens of the second generation Chiron RIBA-2 assay (Chiron Corporation, Emeryville, Calif.), while infection with divergent HCV genotypes elicited antibodies mainly reactive to c22-3 and c33c. Reactivities with antibodies 5-1-1 and c100-3 were infrequent and were generally weak, irrespective of the geographical origin of the donor. Because the envelope region of HCV is even more variable than the NS-4 region, it is likely that vaccines based on these proteins need to be multivalent and perhaps specifically adapted for different geographical regions.