A respiratory virus for which there is no vaccine or treatment is spreading in parts of California — but there’s no need to sound the alarm yet, public health officials say.
Most communities in Northern California have seen high concentrations of human metapneumovirus, or HMPV, detected in their wastewater, according to data from the WastewaterScan Dashboard, a public database that monitors sewage to track the presence of infectious diseases.
An analysis of data by the Los Angeles Times found that the communities of Merced in the San Joaquin Valley, and Novato and Sunnyvale in the San Francisco Bay Area saw increased levels of HMPV in their wastewater between mid-December and late February.
HMPV has also been detected in LA County, although at levels considered low to moderate at this point, the data show.
Although HMPV may not actually cause symptoms, it is not a new virus. Its typical seasonal distribution pattern was enhanced by the COVID-19 pandemic, and its re-emergence could indicate a return to the normal pre-coronavirus respiratory disease pattern.
Here’s what you need to know.
What is HMPV?
HMPV was first discovered in 2001, according to the US Centers for Disease Control and Prevention. We are spread by being close to a person with this virus or by touching a dirty place, said Dr. Neha Nanda, chief of infectious diseases and epidemiologist at USC’s Keck Medicine Hospital.
Like other respiratory diseases, such as the flu, HMPV spreads and lasts longer in cold temperatures, infectious disease experts say.
Human metapneumovirus cases usually begin to appear in January before peaking in March or April and ending in June, said Dr. Jessica August, chief infectious disease officer at Kaiser Permanente Santa Rosa.
However, as was the case with many respiratory viruses, COVID disrupted that seasonal trend.
Why are we talking about HMPV now?
Before the pandemic hit in 2020, Americans were regularly exposed to seasonal viruses like HMPV and developed natural immunity, August said.
That protection was reduced during the violence, as people stayed at home or distanced themselves from others. So when people resumed normal activities, they were more vulnerable to the virus. Unlike other viruses, there is no vaccine for human metapneumovirus.
“That’s why after this pandemic we saw record-breaking viral infections in children because we didn’t have the usual defenses we had, because we didn’t explain anything,” said August. “All of that also led to longer viral seasons, more severe illness. But all of these things have stabilized in many ways.”
In 2024, national testing for HMPV reached 11.7% at the end of March, according to the National Respiratory and Enteric Virus Surveillance System. The next year’s high was 7.15% in late April.
So far this year, the highest test rate on record was 6.1%, reported in Feb. 21 — the latest date for which complete data is available.
Although the seasonal spread of viruses such as HMPV is not new, people are more aware of infectious diseases and how to protect themselves during epidemics, and they have been part of public knowledge for years, said August and Nanda.
What are the symptoms of HMPV?
Most people will not go to the doctor if they have HMPV because it usually causes mild, cold-like symptoms including cough, fever, nasal congestion and sore throat.
HMPV infection can progress to:
- Asthma attacks and active airway disease (wheezing and difficulty breathing)
- Middle ear infection behind the ear drum
- Croup, also known as “barking” cough – infection of the vocal cords, trachea and large airways in the lungs.
- Narrowing of the airways
- Fever
Anyone can get human metapneumovirus, but those who are immunocompromised or have other underlying medical conditions are at greater risk of developing severe disease – including pneumonia. Young children and the elderly are also considered high-risk groups, Nanda said.
What is the treatment for HMPV?
There is no prescribed treatment protocol or antibiotic for HMPV. However, it is common for the infection to resolve on its own and treatment is mostly directed at relieving symptoms, according to the American Lung Assn.
The doctor will probably send you home and tell you to rest and drink plenty of fluids, says Nanda.
If symptoms worsen, experts say you should contact your healthcare provider.
How to avoid contracting HMPV
Infectious disease experts say the best way to avoid getting HMPV is like preventing other respiratory infections.
Recommendations of the American Lung Assn. include:
- Wash your hands regularly with soap and water. If that is not available, clean your hands with an alcohol-based hand sanitizer.
- Clean frequently touched areas.
- Open a window to improve airflow in tight spaces.
- Avoid being around sick people if you can.
- Avoid touching the eyes, nose and mouth.
Assistant data and graphics editor Vanessa Martínez contributed to this report.
