The U.S. Centers for Disease Control and Prevention (CDC) has issued a health alert about the recent increase in human parvovirus B19 activity in the United States following a surge in the highly contagious respiratory infection, particularly among children.

Parvovirus B19 is a respiratory illness transmitted through respiratory droplets of infected individuals, even if they are without symptoms. It can also be transmitted during pregnancy from the mother to the fetus or through blood transfusion. The virus typically affects young children, but can also infect adults. An individual who is once exposed to parvovirus builds antibodies against it. The infection is known as the "fifth disease" as it was the fifth of the common childhood illnesses identified.

The signs of infection include fever, headache, sore throat, joint pain, and cough. Since parvovirus infection also causes red rashes on the cheeks, it is called "slapped cheek disease." The rash, however, is not contagious, and the infection spreads in the week before the rash appears.

"In the first quarter of 2024, public health authorities in 14 European countries observed unusually high numbers of cases of parvovirus B19. In the United States, there is no routine surveillance for parvovirus B19, and it is not a notifiable condition. Recently, CDC has received reports indicating increased parvovirus B19 activity in the United States," the CDC health advisory stated.

According to the CDC report, the blood plasma test results from a large commercial laboratory indicate a general increase in parvovirus infection cases across all age groups, rising from less than 3% during 2022–2024 to 10% in June 2024. The surge is particularly high among children aged five to nine, with cases increasing from 15% during 2022–2024 to 40% in June 2024. Additionally, there have been reports of clusters of parvovirus B19-associated complications among pregnant individuals and those with sickle cell disease.

Parvovirus usually causes a mild infection in children, however, it can lead to complications in pregnant women, immunocompromised, or those with certain blood disorders, if they do not have previous exposure to the virus.

In pregnant women, most cases may resolve without complications, but in 5-10% of cases, there are chances of fetal anemia, non-immune hydrops (a severe condition that causes fluid accumulation in the fetus), or fetal loss. The risk is high when the acute infection occurs between nine and 20 weeks of pregnancy. Treatment generally involves supportive care for the pregnant women and monitoring, and treating the fetus for anemia.

The parvovirus infection is risky for severely immunocompromised individuals such as those with cancers, organ transplants, HIV infection, receiving chemotherapy, or chronic hemolytic disorders such as sickle cell disease, thalassemia, and hereditary spherocytosis. These groups are at higher risk of developing chronic or transient aplastic anemia from the infection.

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