Human Parvovirus Detected in Fremont

Fremont is among California cities where human parvovirus B19 is being flagged this month as a circulating respiratory virus, according to local media reports and federal public health guidance. The virus, also known for causing fifth disease, usually produces mild illness or no symptoms in otherwise healthy people, the Centers for Disease Control and Prevention says. The current concern is sharper for pregnant people and for people with blood disorders or weakened immune systems, who face a higher risk of complications. CDC says parvovirus B19 activity in the United States tends to rise in late winter, spring and early summer, and a 2025 federal report said activity typically peaks in April through June. ### Why are health officials paying attention to parvovirus B19 now? CDC issued a national Health Alert Network advisory on Aug. 13, 2024, warning of increased human parvovirus B19 activity in the United States. The agency said there is no routine national surveillance for the virus and it is not a notifiable condition, but commercial laboratory data and reports of clusters pointed to increased spread. (patch.com) A June 26, 2025 CDC report said the share of serum specimens positive for recent parvovirus B19 infection during January through May 10, 2025, was higher than during the same period in 2024. That report said the pattern suggested sustained transmission after activity in 2024 had already exceeded prepandemic years. ### What exactly is this virus, and how does it spread? Parvovirus B19 spreads through respiratory particles, through blood or blood products, and during pregnancy from mother to baby, according to CDC. (cdc.gov) The agency says the virus infects only people and is not the same as the parvoviruses that affect dogs or cats. CDC says about 1 in 4 people infected with parvovirus B19 have no symptoms. (cdc.gov) When symptoms do appear, they are usually mild and can include fever, headache, cough, sore throat, runny nose, rash, joint pain and muscle aches. A red facial rash often described as a “slapped cheek” rash is more common in children. ### Who faces the biggest risk if they get infected? Pregnant people are one of the main high-risk groups named by CDC. (cdc.gov) The agency says infection during pregnancy can spread to the fetus and can slightly increase the risk of miscarriage and other fetal complications. People with sickle cell disease, thalassemia, hereditary spherocytosis, leukemia, HIV, organ transplants or other causes of weakened immunity also face higher risk, CDC says. (cdc.gov) In those patients, parvovirus B19 can cause a severe drop in blood count and other complications affecting the blood system and other organs. ### When are people most contagious, and what should Fremont residents do? CDC says people are most contagious during the first few days of symptoms and are unlikely to be contagious once later symptoms such as rash or joint pain appear. (cdc.gov) The agency says it is usually safe to return to work or school after the rash appears, though people with anemia or weakened immune systems may remain contagious longer. There is no vaccine or preventive treatment for parvovirus B19, CDC says. The agency recommends core respiratory-virus precautions: cover coughs and sneezes, wash hands well and often, clean frequently touched surfaces, improve indoor air, and take steps to avoid spreading illness when symptoms begin. Frequent handwashing is especially important in child-care settings and health-care facilities. (cdc.gov) ### Where can residents look for official local updates? Alameda County Health says it posts public health alerts, advisories and updates for clinicians, partners and the public on its health alerts page. The county says those notices cover communicable disease outbreaks, immunization updates and other public health concerns. As of Sunday, May 17, 2026, the most detailed public guidance available to residents comes from CDC’s parvovirus B19 pages and Alameda County’s health alert system. (cdc.gov) CDC says pregnant people, and people with blood disorders or weakened immune systems, should contact a health-care provider if they have symptoms or a known exposure. (cdc.gov) (health.alamedacountyca.gov)