Health officials say a respiratory virus spreading in parts of the United States is not new and most people should not panic, even as cases increase in California and other states.
Human metapneumovirus, known as HMPV, is circulating this season with rising cases reported in California and New Jersey. The virus has no vaccine and no specific antiviral treatment, but experts say most infections are mild and resolve on their own.
Data from the U.S. Centers for Disease Control and Prevention shows HMPV has been increasing since November 2025. The virus accounted for more than 5% of positive respiratory virus tests during the week of Feb. 14 through Feb. 21, according to the agency’s respiratory surveillance dashboard.
The uptick is part of a broader seasonal pattern of respiratory illnesses that includes Respiratory Syncytial Virus, COVID-19 and seasonal flu.
Wastewater monitoring data also shows elevated levels of the virus in Northern California, including in Sacramento, San Francisco, Davis and Vallejo.
“HMPV causes symptoms very similar to RSV,” said Dean Blumberg, chief of pediatric infectious diseases at UC Davis Health. “This includes upper respiratory symptoms that sometimes progress to pneumonia or bronchiolitis and wheezing.”
HMPV was first identified in 2001 and belongs to the same viral family as RSV. The virus spreads through respiratory droplets from coughing or sneezing, close personal contact, and touching contaminated surfaces before touching the mouth, nose, or eyes.
Common symptoms include cough, fever, nasal congestion and sore throat. Most cases last four to five days, though some patients can develop bronchitis or pneumonia.
Young children, older adults, and people with weakened immune systems face the highest risk of serious illness.
Health experts say prevention measures are similar to those used for other respiratory viruses. People should wash their hands frequently, cover coughs and sneezes and stay home when sick to limit the spread.