Surveillance of blood donors detects an exceptional Parvovirus B19 outbreak in Switzerland in 2023/2024

Human Parvovirus B19 is a common human pathogen that causes fifth disease that can be severe for immunocompromised people and unborn children. Blood donations are routinely screened for the presence of Parvovirus B19 DNA to release plasma for the fractionation industry.

Voluntary, unremunerated blood donations from six regions of Switzerland were tested by Interregional Blood Transfusion Swiss Red Cross since 2008. Individual blood donations with viral titers exceeding 10³ IU/mL are removed from the blood supply and the viral genotype, viral titers, and serological status were determined.

From 2008 until September 2024, 2,789,113 blood donations were tested for the presence of Parvovirus B19 DNA, of which 271 were considered positive. Two small outbreaks in the years 2013 and 2017 and an unprecedented massive outbreak in winter/spring 2023/2024 were detected. The incidence in the 2023/2024 outbreak was 15.1 per 10,000 donations and thus about ten times higher than in the previous outbreaks with 1.6 and 1.2 positive cases per 10,000 donations, respectively. Of the genotyped cases from the 2023/2024 outbreak all were caused by Parvovirus B19 of genotype 1a2. Viral titers reached maximum values of 3×10¹² IU/mL. Serological data show an inverse correlation between viral titers and presence of protective IgG antibodies.

Similar to the situation in other European countries, Switzerland was struck with an unprecedented Parvovirus B19 outbreak in 2023/2024. The outbreak follows a two-year stretch with no positive Parvovirus B19 cases. It is likely that the measures implemented in 2020 to confine the spread of SARS-CoV-2 had a strong impact on other infectious diseases like Parvovirus B19.