NAPA, CA — A very contagious respiratory illness is spreading throughout several Northern California cities, including Napa, according to recent wastewater surveillance data.
While generally mild, the circulating parvovirus B19 is raising concerns due to its severe potential complications in pregnant people.
Data indicates a moderate presence of parvovirus B19 across multiple Northern California locations, including Fremont, Napa, Novato, Redwood City, San Rafael and neighborhoods in San Francisco. The virus, which is transmitted from human to human, is distinct from parvovirus type 2, which infects dogs, according to the American Veterinary Medical Association.
The cities that have reported the virus’ presence include:
The virus typically presents with mild symptoms such as fever, muscle aches, and a runny nose, according to the CDC. A 2026 study found that children between the ages of 5 and 15 may develop a distinguishing rosy, slapped cheek rash, often referred to as fifth disease, approximately one week after infection, according to the Cleveland Clinic.
Crucially, pregnant individuals face a higher risk of severe complications, including miscarriage, according to the CDC.
The virus shows seasonal variation, peaking during late winter and spring, as detailed in the 2026 study.
While infection with parvovirus B19 typically manifests as a mild condition in healthy adults and children, it can occasionally lead to significant medical issues, potentially impacting vital organs and systems, including the heart, liver, kidneys, brain, or blood, the CDC reported. Individuals with compromised immune systems or specific pre-existing blood disorders — such as hereditary spherocytosis, thalassemia, or sickle cell disease — may experience a dangerous decline in red blood cell levels, known as anemia, following infection.
According to the CDC, certain medical conditions place individuals at a higher risk of severe complications from the virus, including leukemia or various other oncological conditions, a history of an organ transplant, HIV infection, and chronic blood disorders like thalassemia or sickle cell disease.
Although the virus is not routinely monitored in the U.S., the CDC has noted increased rates in 2024 and 2025 compared to previous years, a trend local health experts suggest could be linked to the pandemic.
There is no vaccine or specific treatment available for parvovirus B19, according to the CDC.
To limit the transmission of parvovirus B19, health experts recommend following foundational respiratory virus prevention methods:
Health experts particularly advise pregnant people to wash their hands often and avoid close contact in high-risk settings like schools and daycare centers where the virus has been confirmed. The CDC further advises staying home when experiencing respiratory illness.
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