California is experiencing a rise in human metapneumovirus (HMPV), a common respiratory virus, particularly in Northern California communities. While the increase is being monitored through wastewater surveillance, public health officials emphasize there’s currently no cause for widespread concern. The resurgence of HMPV, which doesn’t have a specific vaccine or treatment, is prompting renewed attention to respiratory illnesses as the state moves further from the heightened protections of the COVID-19 pandemic.
Data from the WastewaterScan Dashboard, a public database tracking infectious diseases through sewage analysis, indicates elevated concentrations of HMPV in a majority of Northern California communities. A Los Angeles Times analysis pinpointed increases in HMPV levels in wastewater samples from Merced in the San Joaquin Valley, and Novato and Sunnyvale in the San Francisco Bay Area between mid-December and the end of February. The virus has also been detected in Los Angeles County, though at lower levels.
What is Human Metapneumovirus?
First identified in 2001, according to the U.S. Centers for Disease Control and Prevention, HMPV is transmitted through close contact with infected individuals or by touching contaminated surfaces. Like influenza, the virus thrives in colder temperatures, making it a seasonal concern for infectious disease experts. Typically, HMPV cases begin appearing in January, peak in March or April, and decline by June, explained Dr. Jessica August, chief of infectious diseases at Kaiser Permanente Santa Rosa.
However, the COVID-19 pandemic disrupted this typical seasonal pattern. Before 2020, regular exposure to seasonal viruses like HMPV helped build a degree of natural immunity within the population. As people limited social interactions during the pandemic, that immunity waned, leaving individuals more susceptible when normal activities resumed. “Unlike other viruses, there isn’t a vaccine for human metapneumovirus,” Dr. August stated. “That’s why after the pandemic we saw record-breaking childhood viral illnesses because we lacked the usual immunity that we had, just from lack of exposure.”
Tracking the Spread and Recent Trends
In 2024, the national test positivity rate for HMPV peaked at 11.7% at the end of March, according to the National Respiratory and Enteric Virus Surveillance System. The following year, in late April, the peak was 7.15%. As of February 21, 2026 – the most recent date with complete data – the highest test positivity rate recorded this year was 6.1%. This suggests a gradual settling of viral seasons after the disruptions caused by the pandemic.
The increased awareness of infectious diseases fostered during the pandemic has also contributed to a heightened public consciousness regarding preventative measures, according to Dr. Neha Nanda, chief of infectious diseases and hospital epidemiologist for Keck Medicine of USC. “People became more aware of infectious diseases and how to prevent them during the pandemic, and they’ve remained part of the public consciousness in the years since,” she noted.
Symptoms and Who is at Risk
Most individuals experiencing HMPV infection won’t require a doctor’s visit, as symptoms are typically mild and resemble a common cold, including cough, fever, nasal congestion, and sore throat. However, HMPV can lead to more serious complications, such as asthma attacks, reactive airway disease (wheezing and difficulty breathing), middle ear infections, and croup – an infection of the upper airways.
Individuals who are immunocompromised or have underlying medical conditions are at a higher risk of developing severe illness, including pneumonia. Young children and older adults are also considered particularly vulnerable groups, Dr. Nanda explained.
Treatment and Prevention
Currently, there is no specific treatment protocol or antiviral medication for HMPV. Treatment generally focuses on managing symptoms, with rest and adequate fluid intake being the primary recommendations, according to the American Lung Association. If symptoms worsen, seeking medical attention is advised.
Preventing the spread of HMPV involves similar measures used to prevent other respiratory illnesses. The American Lung Association recommends frequent handwashing with soap and water (or using an alcohol-based hand sanitizer when soap and water aren’t available), cleaning frequently touched surfaces, improving air circulation in crowded spaces, avoiding close contact with sick individuals, and avoiding touching the eyes, nose, and mouth.
As we continue to navigate the evolving landscape of respiratory viruses, ongoing surveillance and public health awareness remain crucial. While the current rise in HMPV doesn’t warrant alarm, it serves as a reminder of the importance of preventative measures and staying informed about circulating illnesses.
What questions do you have about respiratory viruses this season? Share your thoughts in the comments below.
Disclaimer: This information is intended for general knowledge and informational purposes only, and does not constitute medical advice. It is essential to consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.