Nico Lelie

The efficacy of different screening scenarios in reducing hepatitis B virus (HBV) transmission risk as compared to the risk without screening was modeled in 9,337,110 donations from four geographical regions that had been subjected to hepatitis B surface antigen (HBsAg) and individual donation nucleic acid amplification testing (ID-NAT). We used the Weusten models for estimating infectivity risk for Red Blood Cell (RBC) transfusions in eight HBV infection stages and then evaluated multiple screening strategies based on minipool (MP) and ID-NAT options of different sensitivity for their efficacy in reducing this risk. The efficacy in reducing HBV transmission risk by screening scenarios across the regions varied between 81% (HBsAg only) and 99.2% (ID-NAT and anti-HBc). Highly sensitive ID-NAT alone achieved a slightly higher risk reduction (97.6–99.0%) than minipool of 6 donations (MP6)-NAT in combination with HBsAg and anti-HBc (96.3–98.7%). In ID-NAT screened lapsed and repeat donors, the additional risk removed by HBsAg testing was minimal (<0.1%). The modeling outcomes in this and two previous reports using this multi-regional database suggest that one could consider an ID-NAT alone testing scenario as an alternative to MP-NAT and serology-based testing algorithms and restrict serologic testing to first-time donors only.

The Common Specifications/EU 2017/746 regulation for market approval of class D in vitro diagnostic devices (IVDs) intended for detection of blood borne viruses requires testing of the International Standard and 10–30 seroconversion panels to demonstrate ‘state of the art’ assay performance. We examined whether these requirements for performance evaluation are reasonable for HBV-DNA and HBsAg assays. For this purpose, we quantified HBsAg and HBV-DNA (genotype A) in the ramp-up phase of five seroconversion panels and demonstrated a remarkably parallel increase in the Log concentration of both analytes over time. Testing of seroconversion panels by three nucleic acid amplification technology (NAT) methods in multiple replicates and probit analysis with sufficient critical samples from all five panels taken together showed detection limits in copies/mL that were comparable to those on a HBV-DNA genotype A standard dilution panel. This indicates that the viral doubling time in the ramp-up phase is equal above and below the quantification limit of the viral load assay. The geometric mean HBsAg (PRISM) cutoff crossing point was 20 days later than the 50% NAT (Ultrio Plus) conversion point equivalent to 1500 (range: 1100–2200) and 4.8 (CI: 3.7–6.4) HBV-DNA copies/mL, respectively. Analytical sensitivity data of different NAT assay versions obtained over a decade demonstrated that the detection limit on the International Standard is not representative of all genotyped reference samples. From our detailed mathematical analysis, we conclude that HBV-DNA and HBsAg standard dilution series are functionally equivalent to seroconversion panels. A general requirement of a 95% detection limit ≤100 HBV-DNA copies/mL for different viral genotypes would be a better-defined regulation for EU market approval of NAT blood screening assays than the testing of multiple seroconversion panels to claim ‘state of the art’ performance.

HBV infectivity data were reviewed and the 50% infectious dose (ID₅₀) was reassessed in different HBsAg positive infection stages enabling modelling of transfusion‐transmitted (TT)‐HBV infection risk if HBsAg donor screening was replaced by individual donation nucleic acid amplification technology (ID‐NAT). Quantitative HBsAg and HBV‐DNA assays were performed against international standards to compare the ratio between potential infectious HBV virions and subviral HBsAg particles in Egyptian HBsAg positive blood donors as well as in Japanese chimpanzee samples of known infectivity. HBV‐DNA load below the quantification limit of detection was estimated against a reference standard by replicate NAT testing (n = 25). Infectivity of chimpanzee samples collected during ramp‐up and declining viremic phase were tested in a human liver chimeric mice (HLCM) model and compared with published infectivity data from different HBsAg positive infection stages. Lowest estimates of ID₅₀ in HBsAg positive plasma were 3–6 HBV virions in chimpanzee studies. Infectivity decreased approximately 10–100‐fold in the declining viremic phase using HLCM. In acute‐phase samples, HBV to HBsAg particle ratios varied between 1:10²–10⁴ but in HBsAg positive blood donors this particle ratio reached 1:10⁶–10¹² when viral load was below 100 HBV‐DNA copies/ml. Modelled TT‐HBV risk of an HBsAg positive/ID‐NAT nonreactive blood transfusion was estimated at 9%–46% for components containing 20–200 ml of plasma assuming an ID₅₀ of 316 (point estimate between 100 and 1000) virions. In the Egyptian setting, discontinuation of HBsAg donor screening and reliance on ID‐NAT alone seems to be unsafe.

Background: The residual transfusion‐transmitted hepatitis B virus (TT‐HBV) risk with different testing strategies depends on the sensitivity of screening assays, the prevalence of hepatitis B surface antigen (HBsAg) compared to HBV‐DNA in window period (WP) and occult HBV infections (OBIs), and infectivity of blood in these infection stages. We compared modeled WP and OBI transmission risk in a multiregional individual donation nucleic acid amplification technology (ID‐NAT) screening study with observed TT‐HBV infection rates in several lookback studies.Study design and methods: The WP and OBI risk was estimated from ID‐NAT screening data in six geographic regions. The 50% infectious dose (ID₅₀), a key factor in the applied risk models, was assumed to be 100‐fold higher in OBI than in WP blood. The relative proportion of WP and OBI TT‐risk was estimated for different screening scenarios and expressed as a percentage of the ID‐NAT yield rate to allow for comparison with observed TT‐rates in lookback studies.Results: Despite sevenfold to eightfold higher HBV ID‐NAT yield rates in OBI than WP in South‐East Asia and Europe, our models predicted that 40 (26–55)% of total residual TT‐HBV risk was due to OBI, comparable to 37% observed in a Japanese hemovigilance study. Modeled TT‐OBI risk was approximately 10‐fold higher than observed rates of 2%–8% in five lookback studies but comparable to one other study (36%).Conclusion: Although the observed TT‐OBI rate was generally lower than the modeled risk, the relative risk of WP versus OBI transmission was not incompatible with the observational infectivity data. This supports the validity of our assumptions in the infectivity‐based models for estimating worst‐case residual risk with different testing scenarios.

Background: The prevalence of hepatitis B surface antigen is estimated to be 6.7% in the South African population and in April 1995 the nation introduced universal hepatitis B virus (HBV) vaccination for newborns and infants. We studied the temporal association of this program with HBV prevalence in young blood donors and the contemporary HBV incidence and residual risk of transfusion‐transmitted HBV infection (TT‐HBV).Methods: We used blood donation data from January 2011 to December 2019. Estimation of HBV prevalence donations made by first‐time blood donors were analyzed by birth cohort and covariates. To estimate the incidence and residual risk of TT‐HBV, mathematical models used data from both first time and repeat donors.Results: HBV prevalence in first‐time donors decreased from 0.84% (95% confidence interval [CI] 0.78–0.90) in 2011 to 0.66% (95% CI 0.61–0.70) in 2019. The post‐1995 birth cohort had a significantly lower HBV prevalence of 0.14% (95% CI 0.13–0.15) than the pre‐1985 birth cohort of 1.29% (95% CI 1.25–1.33) and the odds of HBV infection were reduced in a multivariable model (odds ratio [OR] = 0.28, 95% CI 0.24–0.34). The residual risk of TT‐HBV occurring from window‐period, occult, and possible vaccine breakthrough infections were estimated at 36.9, 5.8, and 2.2 per million red blood cell transfusions, respectively.Conclusion: Donors born after the start of routine HBV immunization had significantly lower prevalence of HBV infection, supporting the effectiveness of the vaccination program. The contemporary residual risk of TT‐HBV has decreased and should decline further as more vaccinated young people join the donor pool.

Human immunodeficiency virus (HIV) and hepatitis B virus (HBV) are endemic in South Africa while hepatitis C virus (HCV) infection is rare. Two nucleic acid amplification technology platforms, the Procleix Ultrio Elite assay on the Panther instrument (Elite) and the cobas MPX assay on the cobas 6800 or 8800 system (MPX), are used worldwide. In 2015 these were evaluated in South African context. Study Design and Methods The sensitivity of HIV, HBV, and HCV was evaluated using reference panels and 2-fold dilutions of 51 positive plasma samples tested in 12 to 24 replicates. The 95% and 50% lower limits of detection (LOD) were estimated by probit analysis and window period (WP) risk days by the Weusten model. Specificity was established by testing 3646 blood donations individually and instrument performance by evaluating all runs. Results Specificity was 99.94% for MPX and 99.97% for Elite. The following 95% LODs (95% confidence intervals [CIs]) were estimated for MPX and Elite, respectively: HBV, 17.8 (10.9-33.9) and 47.9 (29.1-92.4) cp/mL; HCV, 21.9 (15.3-34.6) and 13.8 (8.9-24.0) cp/mL; and HIV, 8.3 (5.5-14.7) and 10.4 (6.9-18.2) cp/mL. On SA HBV and HIV dilution panels, relative sensitivity (range) of MPX was 3.20 (1.26-6.50) and 1.42 (0.26-2.72) fold higher than Elite. Downtime on cobas 6800 was 26 hours vs 6.6 hours on Panther (P < .001). We estimated infectious WPs for HBV, HCV, and HIV-1 at 13.8, 1.8, and 2.6 days for Elite and 10.3, 2.1, and 2.4 days for MPX. Conclusion Although MPX was significantly more sensitive for HBV, Elite was implemented due to instrument reliability during evaluation.

The World Health Organization (WHO) recommends the clinical use of a human immunodeficiency virus 1 (HIV‐1) viral load (VL) threshold level of 1000 copies (cp)/mL in patients on antiretroviral therapy (ART) to distinguish between viral control (VL < 1000 cp/mL) and viral failure or poor adherence (VL > 1000 cp/mL). The accuracy of five quantitative HIV‐1 RNA assays at this level was compared by replicate testing (n = 24) of 1000 cp/mL samples prepared from the Viral Quality Control (VQC) HIV‐1 subtype B standard, which is in use for validation of nucleic acid testing methods since 1995. Until 2004 the VL assays reported geometric mean (95% confidence interval [CI]) values ranging between 449 (188‐1067) and 3162 (3057‐2367) cp/mL when using the Siemens bDNA 3.0 assay as reference method for an assigned value of 1000 (962‐1038) cp/mL. In 2018, the following values (95% CI) were found by 24 replicate tests in each of the VL assays on the 1000 cp/mL samples: Abbott RealTime 1084 (784‐1572), BioMerieux EasyQ 1110 (533‐2230), Roche CAP/CTM 1277 (892‐1828), Hologic Aptima 1616 (1324‐1973), and Cepheid GeneXpert 2502 (1713‐3655) cp/mL. Calibration studies involving three consecutive WHO replacement standards showed a significant drift in the amount of RNA copies per International Unit overtime. Heat inactivation of HIV‐1 standards was found to cause a destandardizing effect. Our study underlines the limitations in HIV‐1 RNA assay calibration based on frequently replaced WHO international standards. It is therefore proposed that clinicians interpret the recommended 1000 cp/mL alert level in therapy monitoring with an inaccuracy range of 500 to 2000 cp/mL.

Background and Objectives: Comparison of two models for estimating residual transfusion transmission risk by NAT screened window period (WP) donations in South African repeat donors gave identical results for HIV but not for HBV. In order to understand discrepant HBV modelling outcomes, the values of input parameters in three HBV WP risk models were reviewed and subsequently applied to the same South African screening data generated by HBsAg PRISM and two NAT assays (Ultrio and Ultrio Plus). Two of the models were also compared using individual donation (ID)‐NAT screening data from different geographical regions.Methods: Values of input parameters were derived from two published data sources and used in three risk models [(1) the incidence rate–WP risk day equivalent model, (2) the NAT yield WP ratio model and (3) the anti‐HBc‐negative HBsAg yield period ratio model] and subsequently applied to the same ID‐NAT screening data.Results: The HBV WP transmission risk in South African repeat donations during a one‐year Ultrio Plus NAT screening period was estimated as 22, 43 and 17 per million, respectively, for the three models, as compared to 56, 117 and 48 per million for HBsAg PRISM screening. The approximate two‐fold higher estimate calculated with the NAT yield WP ratio model was corroborated in repeat donations from three of four regions in a multi‐regional study. When another set of model input values (with shorter viraemia periods and a higher proportion of acute occult infections) was applied to the South African screening data, the relative difference in risk estimates between the three models became smaller.Conclusions: Window period risk modelling for HBV is more complex than for HIV. Multiple factors affect the modelling outcomes. These include the values used for the length of transient HBsAg and HBV‐DNA‐positive phases, the proportion of acute occult and vaccine breakthrough infections and the assumption of random appearance of donors throughout the entire acute resolving infection phase. A substantial proportion of HBV WP NAT yields have very low viral load and lack donor follow‐up data calling into question their definitive classification into the early acute (infectious) replication stage. Since these possible WP NAT yields most highly impact the NAT yield WP ratio model, we recommend relying on the more conservative estimates of the incidence rate–WP risk day equivalent model.

BACKGROUND: If anti‐hepatitis B core antibody testing is not mandated blood donors with occult hepatitis B infection (OBI) may transmit hepatitis B virus (HBV) to a recipient in spite of the use of nucleic acid amplification technology (NAT) or pathogen inactivation (PI).STUDY DESIGN AND METHODS: We developed a model to estimate OBI transmission risk based on three components: the probability distribution of the viral load (VL) in a randomly selected OBI donor, the probability that a given VL remains undetected, and the probability that this VL causes infection in the recipient. A subset of 217 South African OBI samples identified by individual donation (ID)‐NAT screening were quantified by replicate testing using an ID‐NAT assay (Ultrio Plus) against HBV DNA standard dilution series. The observed log VLs could be described by a Gumbel distribution. A correction was included to compensate for OBI samples missed by initial ID‐NAT screening.RESULTS: The model estimates that 3.3% of all OBI donations are undetected by ID‐NAT (Ultrio Plus) and cause infection by a blood component containing 20 mL plasma, going up to 8.7% when using minipools of 6 (MP6)‐NAT. For 200‐mL plasma transfusion these risks were estimated at 14 and 28%, respectively, while PI with modest (2 log) reduction capacity would reach 4.8% without NAT and 1.3 or 0.4% when combined with MP6‐ or ID‐NAT.CONCLUSION: The model can be used to compare different screening and/or PI strategies in reducing viral transmission risk and could serve as a tool in evaluating efficacy of alternative blood safety scenarios.