Assessment of risk of infection through blood transfusion requires correlation of donor risks, epidemiological data (local incidence and prevalence of infection) and screening assay performance. Blood programs in industrialized countries maintain blood safety surveillance programs for transmissible infections and all blood services should aim to have this in place, as local data is essential to inform assessment. 

Inadvertent recent or long past exposure to infectious agents or non-compliance with selection criteria by donors are still reasons behind infections identified in new or returning blood donors. Given the sensitivity of screening algorithms used, risk of missing infections is highest when the infection has happened in the very recent past and the donor is asymptomatic, undergoing very early stages of infection. Generic deferral due to recent acute viral-like illness and relevant travel broadly takes care of many potentially transmissible infections, whereas national donor selection guidelines will contain required acceptance criteria that must adhered to.