Public health officials say a respiratory virus for which there is no vaccine or specific treatment is spreading in parts of California, but there’s no need to sound the alarm just yet.
High concentrations of human metapneumovirus (HMPV) have been detected in wastewater from most communities in Northern California, according to the WastewaterScan Dashboard, a public database that monitors wastewater to track the presence of infectious diseases.
A Los Angeles Times data analysis found that HMPV levels increased in wastewater from mid-December to the end of February in the Merced community in the San Joaquin Valley and in the San Francisco Bay Area communities of Novato and Sunnyvale.
Data shows HMPV has also been detected in Los Angeles County, but current levels are considered low to moderate.
While HMPV may not necessarily attract attention, it is not a new virus. Its typical seasonal transmission patterns were upended by the COVID-19 pandemic, and its resurgence may mark a return to a more typical pre-coronavirus respiratory disease pattern.
Here’s what you need to know.
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What is HMPV?
HMPV was first detected in 2001, according to the Centers for Disease Control and Prevention. The virus is spread through close contact with an infected person or contact with contaminated surfaces, said Dr. Neha Nanda, chief of infectious diseases and a hospital epidemiologist at the Keck School of Medicine of USC.
Infectious disease experts say HMPV spreads like other respiratory illnesses like the flu and is more likely to persist in cold temperatures.
Dr. Jessica August, chief of infectious diseases at Kaiser Permanente in Santa Rosa, said human metapneumovirus cases typically start showing up in January, peak in March or April, and then taper off in June.
However, as is the case with many respiratory viruses, the COVID-19 pandemic has disrupted this seasonal trend.
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Why are we talking about HMPV now?
August said that before the 2020 pandemic, Americans were frequently exposed to seasonal viruses like HMPV and developed some degree of natural immunity.
During the pandemic, this protection diminishes as people stay home or distance themselves from others. Therefore, when people resume normal activities, they are more susceptible to contracting the virus. Unlike other viruses, there is no vaccine for human metapneumovirus.
“That’s why in the wake of the pandemic we’re seeing record-breaking numbers of viral illnesses in children because we lack the usual immunity, just from lack of exposure,” August said. “All of this also leads to longer viral seasons and more severe disease. But all of these things have stabilized in a lot of ways.”
According to data from the National Respiratory and Enterovirus Surveillance System, in 2024, the national HMPV test positivity rate peaked at 11.7% at the end of March. The peak of the following year occurred in late April at 7.15%.
The highest test positivity rate recorded so far this year was 6.1%, reported on February 21 – the latest date for which complete data is available.
August and Nanda said that while the seasonal spread of viruses like HMPV is nothing new, people have become more aware of infectious diseases and how to prevent them during the pandemic, and they have remained part of the public consciousness in the years since.
What are the symptoms of HMPV?
Most people don’t see a doctor if they’re infected with HMPV because it usually causes mild cold-like symptoms, including cough, fever, nasal congestion, and sore throat.
HMPV infection can progress to:
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Asthma attacks and reactive airway disease (wheezing and dyspnea)
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Middle ear infection behind the eardrum
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Croup, also known as “barking cough” – an infection of the vocal cords, windpipe, and sometimes the larger airways in the lungs
Anyone can be infected with human metapneumovirus, but those who are immunocompromised or have other underlying medical conditions are particularly at risk of severe illness, including pneumonia. Nanda said young children and the elderly are also considered high-risk groups.
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What is the treatment for HMPV?
There are no specific treatment options or antiviral drugs for HMPV. However, the infection usually goes away on its own, and treatment is focused on relieving symptoms, according to the American Lung Association.
Nanda says your doctor will likely send you home and tell you to rest and drink plenty of fluids.
If symptoms worsen, experts suggest you should contact your healthcare provider.
How to avoid getting infected with HMPV
Infectious disease experts say the best way to avoid getting HMPV is similar to preventing other respiratory illnesses.
Recommendations from the American Lung Association include:
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Wash your hands often with soap and water. If not, use alcohol-based hand sanitizer to clean your hands.
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Clean frequently touched surfaces.
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Open windows to improve air circulation in crowded spaces.
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If possible, avoid being around sick people.
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Avoid touching your eyes, nose and mouth.
Assistant data and graphics editor Vanessa MartÃnez contributed to this report.
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This story originally appeared in the Los Angeles Times.
