Human parvovirus B19, the virus behind “fifth disease” or the so-called “slapped cheek” rash in children, has seen elevated activity in the U.S. since 2024, according to the Centers for Disease Control and Prevention (CDC). Wastewater surveillance from WastewaterSCAN has also detected the virus in communities across the country, including moderate levels recently reported in parts of Northern California near Sacramento, San Jose, Palo Alto, Napa, Davis, and southeastern San Francisco.

The virus spreads primarily through respiratory droplets released when infected people cough or sneeze. Most infections are mild, especially in children, but the illness can sometimes lead to more serious complications in pregnant people and immunocompromised individuals.