For almost fifty years, improvements in donor selection and screening have led to a continuous reduction in the risk of transfusion-transmitted hepatitis B virus (HBV). However, transmission can still occur when blood is collected from hepatitis B surface antigen (HBsAg) negative donors during the pre-seroconversion window period. Another source of transmission is represented by donors with occult HBV infection (OBI), a condition characterised by persistent HBV carriage in the absence of detectable HBsAg. In many countries, this prompted the introduction of nucleic acid testing (NAT) for HBV and/or antibodies to hepatitis B core (anti-HBc) testing in order to improve detection of infectious donations.
In principle, the implementation of both HBsAg and anti-HBc, and HBV NAT provides optimal safety levels as it permits the window phase of acute infection, persistent occult infection, and HBV variant strains to be detected. However, NAT screening is costly, and it is usually beyond the budget of low income countries. On the other hand, anti-HBc has good sensitivity but very low specificity in detecting infectious donations, and therefore its use is limited to regions at lower prevalence, where donor deferral is sustainable in terms of donation wastage1.
The residual risk of transfusion transmission of HBV varies, therefore, worldwide, being greater in low and intermediate income countries, where the prevalence of the virus is higher and the implementation anti-HBc testing and/or NAT for HBV DNA is not affordable. However, the risk might not be negligible even in developed countries using HBV DNA but not anti-HBc, as the minimal infectious dose of OBI is below the limit of detection of current individual NAT assays2.
The transfusion transmission of OBI has a global relevance, the impact of transmissions is frequently underestimated, and the best preventive strategies to improve safety should be tailored to local prevalence and available resources.
In the study of Velati et al. incidence in Italy is low perhaps due to the fact that anti-HBc screening was voluntarily adopted by many Italian blood centres during the period of study but
Italian data do not necessarily extend to other countries ; for example recently study by DIderot-Fopa et al. documented that 1 in 200 blood units released for patient transfusions in Cameroon contain HBV viraemia and could transmit the infection.
Exists a gap between low- and high-income countries in terms of quality and safety of blood suppliesand the need for safe blood products remains unmet.
Blood Transfusion. 2019
Uncovering occult hepatitis B in blood donations: a tale of two worlds
Daniele Prati,Luca Valente.