In Morbidity and Mortality Weekly Report, three new studies describe increased infections of parvovirus B19 detected in US commercial labs, with five worrisome cases in pregnant Minnesotans and infections in children and teens with sickle cell disease in Georgia.
In August, the Centers for Disease Control and Prevention (CDC) issued a Health Alert Network advisory on the rise in cases of the seasonal respiratory viral disease after receiving reports of lab test positivity and clusters of parvovirus B19–related complications among pregnant women and people with sickle cell disease. Several European countries had observed significant increases in B19 activity early in 2024.
The illness, which can increase the risk of miscarriage early in pregnancy, is characterized by a "slapped-cheek" rash in children and joint pain in adults. While most cases are asymptomatic or mild, people with an underlying blood disease or a weakened immune system can experience more serious outcomes.
"B19 infection can be transmitted from a mother to the fetus during pregnancy and, rarely, through transfusion of blood components and certain plasma derivates," the authors of the lab study wrote. "Most persons become infected with B19 during their school years. Immunity from infection is thought to be lifelong."
Almost 10% positivity, up from 1.5%
In the first of the three studies, researchers from North Carolina's Labcorp and the CDC investigated an uptick in parvovirus B19 test positivity at Labcorp in 2024 from levels in the 2018-19 respiratory virus season. Parvovirus B19 is not a notifiable illness in the United States.
The investigators looked for the presence of immunoglobulin (Ig) M antibodies, a marker of recent infection, in clinical specimens from 359,445 children and adults and performed B19 nucleic acid amplification testing (NAAT) in plasma from an average of 1,059 donor pools each month.
Health care providers caring for pregnant persons should be particularly vigilant for signs of reduced fetal movement or evidence of hydrops [severe swelling] which could be associated with B19.
The percentage of IgM-positive clinical specimens climbed to 9.9% in spring 2024, up from less than 1.5% in 2020 to 2023, higher than peaks in the same period of 2018 (3.8%) and 2019 (5.1%). The prevalence of B19–NAAT-positive plasma-donor pools (512 donations per pool) rose to 20% in June, up from less than 2% in 2020 to 2023 and higher than peaks in spring 2018 (6.7%) and 2019 (7.3%).
Increased parvovirus B19 positivity in both clinical specimens and healthy plasma donors suggests greater community transmission in 2024, the researchers said. "This increase in community transmission is likely due to decreased B19 transmission during the COVID-19 pandemic, resulting from COVID-19 mitigation measures, leading to higher numbers of persons susceptible to B19," they wrote.
The authors urged healthcare providers to promote measures to prevent infection and, along with public health officials, to track adverse B19-related outcomes to reduce severe disease in pregnant women and other high-risk patients. "Health care providers caring for pregnant persons should be particularly vigilant for signs of reduced fetal movement or evidence of hydrops [severe swelling] which could be associated with B19," they concluded.
Four pregnant women had complications, including a miscarriage
For the second study, a team led by investigators from the University of Minnesota and the Minnesota Department of Health (MDH) detailed parvovirus B19 infections in five pregnant women from May to August 2024.
Public health officials should raise awareness about parvovirus B19 activity, including among child care and school providers.
The five patients didn't live in the same community, but four had children in their household, two of whom had ill children. The fifth patient was likely exposed at her job as a childcare provider at a facility in which illnesses characterized by fever and rash were circulating in children.
All patients experienced B19 infections at 13 to 20 weeks' gestation, none of whom had a weakened immune system or blood disorder. One patient experienced a miscarriage at 20 weeks' gestation after fetal hydrops, one had no complications during a 3-month observation period, two fetuses developed severe anemia requiring fetal transfusion, and one fetus developed severe anemia and hydrops, requiring two fetal transfusions. The four latter patients delivered full-term infants without complications.
MDH conducted metagenomic sequencing to generate full genomes using amniotic fluid from two patients, and both samples were genotype 1A, the most common circulating genotype worldwide. Specimens didn't appear to be related through a recent shared source or transmission event.
"Public health officials should raise awareness about parvovirus B19 activity, including among child care and school providers, and provide information about who might be at higher risk for severe B19 disease and when infected children and staff members can return to child care or school after infection," the authors wrote.
Life-threatening anemia in children
The final study, conducted by a Children's Healthcare of Atlanta–led research team, involved 55 children infected with sickle cell disease (SCD) and parvovirus B19 infection from December 2023 to September 2024.
Health care providers should be aware of the risk for complications of B19 infection in children with SCD and have a low threshold for testing when there is clinical suspicion of aplastic crisis.
The incidence of B19 infection associated with aplastic crisis—or life-threatening anemia that occurs when the bone marrow stops making red blood cells—among all children with SCD was 35.6 per 1,000 patient-years, 3.6 times higher than that from 2010 to 2023 (7.78 per 1,000 patient-years).
Increased numbers of B19-associated aplastic crisis cases and incidence occurred in 2014 (34 cases; 19.2 per 1,000 patient-years) and 2019 (30 cases; 14.7 per 1,000 patient-years). Based on clinical suspicion, during 2010 to 2023, a median of 2.9% of all patients with SCD were tested for B19 each year from 2010 to 2023, rising to 6.8% in 2024.
Complications of SCD included acute chest syndrome (27%), splenic sequestration (11%), stroke (3.6%), and nephrotic syndrome (1.8%). Forty-three patients (78%) were given transfusions. One child died unexpectedly at home, but B19 was not confirmed in that case.
"Health care providers should be aware of the risk for complications of B19 infection in children with SCD and have a low threshold for testing when there is clinical suspicion of aplastic crisis," the researchers wrote. "Children and adolescents with SCD and B19 infection should be monitored for complications; early red blood cell transfusion might prevent serious adverse outcomes."
