Parvovirus B19 increasing in US, CDC warns. How to prevent it, recognize symptoms.

More people in the U.S. have become infected with a highly transmissible seasonal respiratory virus that can pose serious risks to pregnant women and people with blood disorders, health officials say.

Parvovirus B19 is transmitted through droplets from symptomatic people and from infected people who don’t show any signs of infection. The virus appears to be spreading this summer based on a range of evidence, blood plasma samples and anecdotal reports, the U.S. Centers for Disease Control and Prevention said Tuesday, issuing a broad warning to health care providers, health agencies and the public.

In its alert , CDC officials said the proportion of people who tested positive for antibodies − an indicator of recent infection − increased across all ages, from less than 3% having immunity from 2022 to earlier in 2024, to 10% of people in June. The greatest increase has been among children ages 5 to 9. In plasma donors, the samples showed the prevalence of the virus DNA jumped from 1.5% in December to 19.9% in June. The CDC noted there have been increasing reports of complications among pregnant women and people with sickle cell disease. In Europe, more than a dozen countries also saw "unusually high numbers of cases" of parvovirus B19 in the first quarter of 2024, CDC's alert said.

Parvovirus B19 is highly infectious. Half of the people exposed in one household can become infected, the CDC said. Similar numbers are seen at schools among students and staff during outbreaks. For most, the infection is mild. Symptoms include fever, headache, cough and sore throat, the CDC said. Common signs can be a fever or flu-like symptoms followed by a reddish “slapped cheek” rash in children. Adults can develop painful and swollen joints that usually last one to three weeks.

Parvovirus B19 can cause severe drops in blood count, or anemia, for people with blood disorders or weakened immune systems. Those at greater risk include people with leukemia or other cancers, organ transplant recipients, people with HIV, and blood disorders such as sickle cell and thalassemia. Severe outcomes are rare. They include myocarditis, or inflammation of the heart muscle, encephalitis, or swelling of the brain, and hepatitis.

In pregnant women, the virus can spread to babies. In rare cases, this can cause a miscarriage.

The U.S. does not have routine surveillance for parvovirus B19, nor is it a notifiable condition. There is no vaccine or recommended treatment. Prior infection is thought to give lifelong immunity, the Mayo Clinic said. People can prevent infection by hand-washing and avoiding touching their faces or sharing food. Wearing a mask can also reduce the risk of spread, as with other respiratory illnesses.

This article originally appeared on USA TODAY: Parvovirus B19 increasing in US, CDC warns. How to prevent it, recognize symptoms.