Virological characterization of Parvovirus B19 isolated during the atypical 2023-2024 outbreak in France

Background: A Parvovirus B19 (B19V) outbreak has been reported in Europe in 2023-2024. The aims of this study were 1) to describe the incidence of primary cases from 2012 to 2024 in one French hospital 2) to analyze the genome of 2023 strains 3) to identify virological profiles according to the clinical presentations of B19V infection.

Methods: The incidence of B19V primary cases was studied through an interrupted time-series analysis. Genomes of 2023 strains were sequenced in the NS1-VP1u region. Blood viral loads, IgG and IgM levels were analyzed in 158 cases according to clinical manifestations with Kruskal-Wallis test and a machine learning approach based on k-nearest neighbors.

Results: During the 2023-2024 B19V outbreak, there was an 8-time increase in the incidence of B19V infections compared with pre-pandemic levels (8.25 (95%CI: 5.79-11.76)). The 2023 strains belonged to genotype 1a and were closely related to pre-2019 strains. Blood viral loads were significantly different between clinical presentations (p<0.0001). Machine learning allowed us to classify 68.8% (95% CI: 60.9-75.9) patients into the correct clinical group.

Conclusions: The 2023-24 epidemic is probably due to the reemergence of the pre-2019 strain. The virological profiles highlighted in this study could assist in accurately interpreting virology results.