Abstract
In most persons, human parvovirus B19 (B19) causes a mild respiratory illness, but infection can result in adverse health outcomes in persons who are pregnant, immunocompromised, or who have chronic hemolytic blood disorders. During the first quarter of 2024, several European countries reported increases in B19 activity. In the United States, there is no routine surveillance for B19. To assess increases in B19 activity in the United States, trends in testing and results from two independent populations were examined: 1) the presence of immunoglobulin (Ig) M antibodies, a marker of recent infection, in clinical specimens ordered by physicians and 2) B19 nucleic acid amplification testing (NAAT) in pooled donor source plasma from a large commercial laboratory during 2018-2024. The proportion of IgM-positive clinical specimens reached 9.9% in the second quarter (Q2) of 2024 after remaining <1.5% during 2020-2023 and was higher than Q2 peaks in 2018 (3.8%, p<0.001) and 2019 (5.1%, p<0.001). The prevalence of B19-NAAT-positive donor pools (512 donations per pool) reached 20% in June 2024 after remaining <2% during 2020-2023 and was higher than peaks in 2018 (6.7%, p<0.001) and 2019 (7.3%, p<0.001). Considering the B19 activity increase in the United States in 2024, promotion of measures to prevent respiratory viruses and monitor for adverse B19-related outcomes by health care providers and public health authorities might reduce adverse health outcomes in pregnant persons and others at increased risk.