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The CDC alerted healthcare providers on Tuesday to a dramatic increase in human parvovirus B19 activity in the U.S. and Europe.

The proportion of people with IgM antibodies, an indicator of recent infection, has more than tripled from 2022-2024 to June 2024, from less than 3% to 10%, the agency said in a . The increase has been greatest among children ages 5 to 9 years, rising from 15% to 40% in June 2024.

Moreover, an analysis of donated plasma revealed the prevalence of parvovirus B19 DNA >10⁴ 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 has been linked to serious complications among pregnant people, those with chronic hemolytic blood disorders such as sickle cell disease, and in individuals who are immunocompromised. Parvovirus B19 is not a nationally notifiable illness.

Parvovirus B19 is highly transmissible in respiratory droplets and in many cases is asymptomatic. When symptomatic, infection results in a biphasic illness, particularly in children. The first phase of illness usually occurs about 7 days after infection and is marked by nonspecific symptoms of fever, myalgia, and malaise and lasts about 5 days.

During the second phase, occurring approximately 7 to 10 days after the first phase, children develop a characteristic "slapped cheek" erythematous facial rash. Sometimes a reticulated body rash or arthralgia follows up to several days later. Adults are often asymptomatic until the second phase of the illness when they may develop reticular rash and arthralgia.

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

Of importance, parvovirus B19 can cause chronic or transient aplastic anemia among people with severely immunocompromising illnesses (such as HIV infection or leukemia or other cancers) and chronic hemolytic disorders. It is also a concern in patients with conditions requiring immunosuppressive drugs, such as chemotherapy or organ transplantation.

The CDC urges healthcare providers to have an increased suspicion for parvovirus B19 in patients presenting with symptoms such as fever, rash, joint pain, or unexplained anemia with a low reticulocyte count. They should have a low threshold to test for parvovirus B19 among those at higher risk for severe disease if they have compatible symptoms.

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

In school outbreaks of the virus, up to 50% of susceptible students and staff can be infected. Historically, teachers, daycare workers, and other people working in close contact with children are at high risk of infection. Most people recover completely with supportive care alone and severe sequelae are rare.

The CDC recommends that healthcare providers adhere to standards of care for testing pregnant people if they report exposure to parvovirus B19 or present with signs and symptoms of maternal or fetal parvovirus B19 infection.

People who are at high risk for severe outcomes and work in high-risk settings should practice hand hygiene, avoid sharing of food or drinks, and consider wearing a respirator or mask. In healthcare settings, infection control precautions should be followed for people infected with the virus.

The CDC alert also called on public health departments to raise awareness of parvovirus B19 among healthcare providers and daycare and school providers.

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