Insights into parvovirus B19 clinical and virological dynamics among blood donors

Coinciding with the exceptional European resurgence of human parvovirus B19 (B19V), between 2023 and 2024, twelve B19V DNA-positive blood donations out of 27.737 were detected by the plasma fractionating industry via nucleic acid testing (NAT) and notified to the blood collection centers of Trieste and Gorizia (Italy). In order to prevent potential B19V transmission, the implicated donors were recalled for clinical and virological follow-up for one year. None of the subjects had reported symptoms at the time of donation, though six subjects subsequently recalled either mild, transient symptoms in the days following donation or household exposure to fifth disease. Index viral loads ranged from 6.6×10⁵ to >1.0×10⁹ IU/mL, with the majority of donations exceeding 10⁶ IU/mL. The viral burden exhibited a rapid decline, dropping below 10³ IU/mL after approximately four months and subsequently falling below 5×10³ IU/mL in all the monitored donors by eight months, although low-level viremia persisted. IgG antibodies were detected in all subsequent samples, while IgM persisted for up to 125 days in the majority of donors and remained detectable in three cases, including one instance lasting up to 355 days. Since transfusion-transmitted B19V infection has been documented at viral loads as low as 5×10³ IU/mL, our data suggest that a theoretical risk of transmission may persist for up to nine months. Nevertheless, based on hemovigilance, transfusion-transmitted B19V infection appears to have limited clinical impact, likely due to the high level of population immunity and the pre-dominance of non-infectious viral DNA during the late phase of infection. Overall, these observations support current policies that do not mandate routine B19V screening, while underscoring the importance of targeted testing in high-risk recipients and the temporary deferral of highly viraemic donors for 4-6 months.