Several areas of California are experiencing a rise in a respiratory virus for which there is currently no vaccine or treatment, though public health officials say the situation is not a cause for major alarm at this time.
Data from WastewaterScan, a public database that monitors infectious diseases through wastewater analysis, shows increased concentrations of human metapneumovirus (HMPV) in several communities in Northern California. This monitoring provides an early warning system for potential outbreaks and helps public health officials track the spread of respiratory illnesses.
According to an analysis by the Los Angeles Times, communities in Merced County in the San Joaquin Valley, and Novato and San Rafael in the San Francisco Bay Area, saw increases in virus levels in wastewater between mid-December and the conclude of February.
The virus has also been detected in Los Angeles County, but at levels currently classified as low to medium, according to the data.
Although the name of the virus may be unfamiliar to many, This proves not latest. It was first identified in 2001, according to the Centers for Disease Control and Prevention, and typically spreads through direct contact with an infected person or by touching contaminated surfaces.
Infectious disease experts note that the virus spreads similarly to other respiratory viruses, such as influenza, and is more active during colder weather.
Dr. Jessica August, chief of infectious diseases at Kaiser Permanente in Santa Rosa, explained that cases of the virus typically begin to appear in January, peak in March or April, and then decline by June.
Although, the COVID-19 pandemic disrupted this seasonal pattern. Before the pandemic, people were regularly exposed to seasonal viruses like HMPV, which provided some natural immunity. With social distancing and stay-at-home measures during the pandemic, this exposure decreased, leaving many more susceptible to infection when normal activities resumed.
National data shows that the percentage of positive HMPV tests peaked in 2024 at 11.7% at the end of March, and was 7.15% in late April 2025. This year, the highest positivity rate so far has been 6.1% on February 21.
Symptoms of the Virus
In most cases, HMPV causes mild symptoms similar to the common cold, so many infected individuals do not seek medical attention.
Common symptoms include:
- Cough
- Fever
- Nasal congestion
- Sore throat
Potential Complications
In some cases, the infection can develop into more serious health problems, such as:
- Asthma attacks or wheezing and difficulty breathing
- Ear infections
- Croup (barking cough)
- Bronchitis
- Pneumonia in severe cases
Young children, older adults, and people with weakened immune systems or chronic medical conditions are at higher risk of complications.
Treatment
There is currently no antiviral treatment specific to HMPV. In most cases, the infection resolves on its own, and treatment focuses on relieving symptoms.
Doctors typically advise patients to:
- Rest
- Drink plenty of fluids
- Seek medical attention if symptoms worsen
Prevention
Public health experts recommend following the same preventative measures used to limit the spread of other respiratory illnesses, including:
- Washing hands thoroughly with soap and water
- Using an alcohol-based hand sanitizer when soap and water are not available
- Cleaning frequently touched surfaces
- Improving ventilation in enclosed spaces
- Avoiding close contact with sick people as much as possible
- Avoiding touching the eyes, nose, and mouth
