CDC warns of dramatic increase in human parvovirus B19 cases

The CDC warned health care providers Tuesday that human parvovirus B19 activity is increasing dramatically in the United States and Europe.

The percentage of people with IgM antibodies, an indicator of recent infection, more than tripled from less than 3% between 2022 and 2024 to 10% by June 2024, officials said. Health Alert Network RecommendationsThe increase is strongest among children aged 5 to 9, which is expected to rise from 15% to 40% by June 2024.

Furthermore, analysis of donated plasma revealed a prevalence of parvovirus B19 DNA of ≥10.⁴ IU/mL increased from 1.5% at the end of 2023 to nearly 20% in June 2024.

Parvovirus B19 is a seasonal respiratory virus that is usually associated with mild illness but is known to cause severe complications in pregnant women, people with chronic hemolytic blood diseases such as sickle cell disease, and people who are immunocompromised. Parvovirus B19 is not a nationally reportable disease.

Parvovirus B19 is highly contagious through respiratory droplets and is often asymptomatic. When symptomatic, especially in children, infection causes a biphasic illness. The first stage of the disease usually occurs about 7 days after infection and is characterized by nonspecific symptoms such as fever, myalgia, and malaise, lasting about 5 days.

The second stage occurs about 7-10 days after the first stage, when children develop a characteristic “slapped cheek” erythematous facial rash, sometimes followed a few days later by a reticular rash and joint pain. Adults are often asymptomatic until the second stage of the disease, when they may develop a reticular rash and joint pain.

The virus can be transmitted from mother to fetus during pregnancy. Complications such as fetal anemia, nonimmune hydrops, and fetal loss can occur in 5% to 10% of patients. The highest risk occurs when acute infection occurs between 9 and 20 weeks of pregnancy. Treatment of acute infection during pregnancy is supportive but should also include monitoring and treatment of severe fetal anemia.

Importantly, parvovirus B19 can cause chronic or transient aplastic anemia in patients with severe immunodeficiency diseases (e.g., HIV infection, leukemia, and other cancers) and chronic hemolytic diseases, and is also of concern for patients with conditions requiring immunosuppressants, such as chemotherapy and organ transplants.

CDC urges health care providers to have a high index of suspicion for parvovirus B19 in patients with symptoms including fever, rash, joint pain, and unexplained anemia with low reticulocyte count. A lower threshold for testing for parvovirus B19 should be used in patients at high risk for severe disease when symptoms are compatible.

There is no vaccine to prevent human parvovirus, but antibodies from a previous infection are thought to protect against reinfection. About 50% of adults have detectable antibodies by age 20, and more than 70% of adults have detectable antibodies by age 40.

In a school outbreak, up to 50% of susceptible students and staff may become infected. Historically, teachers, childcare workers, and others in close contact with children have been at high risk for infection. Most people recover fully with supportive care alone, and severe sequelae are rare.

CDC recommends that health care providers follow the standards of care to test pregnant women if they report exposure to parvovirus B19 or if they develop signs or symptoms of maternal or fetal parvovirus B19 infection.

People at high risk of severe outcomes or who work in high-risk environments should practice hand hygiene, avoid sharing food and drink, and consider wearing a respirator or mask. In health-care settings, infection prevention measures should be taken for people infected with the virus.

The CDC's warning called on public health agencies to increase awareness of parvovirus B19 among health care workers, child care providers, and school officials.