CREATING CONFIDENCE

RESEARCH

Residual transfusion transmission risk in later stages of infection

We tested donors with occult HBV infection (OBI), NAT nonreactive HBsAg carriers and NAT nonreactive HIV elite controllers in multiple replicate NAT assays and compared the proportion of reactive results against the reactivity rates on our viral standard dilution panels. From the detection probability curves we can estimate the viral loads below the quantification limits of the viral load assays. This way we were able to establish the viral load distribution in different HBV, HCV and HIV infection stages. These can be used to estimate viral transmission risk with alternative screening scenarios, e.g. if HBsAg, anti-HCV or anti-HIV testing would be discontinued. For OBI transmission risk by blood components in settings without anti-HBc testing we developed a risk model from the observed viral load distribution in occult carriers (after correction of the viral load distribution for OBI donations missed by ID-NAT screening). An OBI transmission risk model spreadsheet is available to estimate the HBV transmission risk as a function of the OBI detection rate. The risk models based on the viral load distributions in copies/mL have been instrumental in establishing the efficacy of different blood screening scenarios in eliminating viral transmission risk (as compared to the theoretical base line risk without blood screening). The same risk models based on viral load distributions in different stages of infection can also be used for estimating the theoretical efficacy of new blood safety scenarios for example a combination of NAT and pathogen inactivation.

An OBI transmission risk model spreadsheet is available to estimate the HBV transmission risk as a function of the OBI detection rate.