California is experiencing a rise in cases of human metapneumovirus (HMPV), a common respiratory virus that typically circulates during the winter and spring months. While not a new threat, health officials are observing higher concentrations of the virus in wastewater across several regions of the state, prompting increased monitoring and public awareness. The situation, while concerning, is not currently considered cause for widespread alarm, but underscores the ongoing challenges of managing respiratory illnesses in a post-COVID-19 landscape.
The increased detection of HMPV is largely thanks to advancements in wastewater surveillance, a public health tool that analyzes sewage for traces of infectious diseases. Stanford University’s WastewaterSCAN, a key player in this monitoring effort, has reported high concentrations of the virus in Northern California communities, including Sacramento, San Francisco, Santa Rosa, Davis, Napa, Marin, Vallejo, and Novato. Southern California is also seeing activity, with San Bernardino County reporting particularly high levels. This data provides an early warning system, allowing public health officials to track the spread of the virus and prepare for potential surges in cases. The Centers for Disease Control and Prevention (CDC) first identified HMPV in 2001, and it has since become recognized as a significant cause of respiratory illness, particularly in young children and older adults.
Understanding Human Metapneumovirus (HMPV)
Human metapneumovirus is a virus that causes respiratory infections, similar to those caused by influenza or respiratory syncytial virus (RSV). Symptoms typically include cough, fever, congestion, and sore throat. Most infections are mild and resolve on their own, but HMPV can lead to more severe illness, especially in vulnerable populations. These include infants, young children, the elderly, and individuals with weakened immune systems or underlying chronic conditions. Severe complications can include pneumonia, bronchitis, and exacerbation of asthma. Currently, there is no specific antiviral treatment or vaccine available for HMPV, meaning care focuses on managing symptoms and preventing the spread of the virus.
The resurgence of HMPV is partly attributed to a decrease in immunity within the population following the COVID-19 pandemic. During the pandemic, widespread public health measures like masking, social distancing, and school closures significantly reduced the transmission of many respiratory viruses, including HMPV. Fewer people were exposed to these viruses and developed natural immunity. Now, with the relaxation of these measures and a return to more normal social interactions, individuals are more susceptible to infection. Dr. Jessica August, head of infectious diseases at Kaiser Permanente in Santa Rosa, explained that HMPV cases typically begin appearing in January, peak in March or April, and then decline by June, but the pandemic disrupted this pattern. The Los Angeles Times reported on this shift in seasonal patterns.
Wastewater Surveillance: A Key Tool for Tracking HMPV
Wastewater surveillance has emerged as a crucial tool for monitoring the spread of infectious diseases. By analyzing samples from sewage treatment plants, public health officials can detect the presence of viruses, even in individuals who are not yet showing symptoms. This provides an early warning system that can help to anticipate outbreaks and allocate resources effectively. The WastewaterScan Dashboard, used in California, is a public database that tracks the levels of various pathogens in wastewater across the state. According to Yahoo News, the data from WastewaterSCAN is informing public health responses at the local, regional, and national levels.
Data from WastewaterScan indicates that HMPV levels peaked nationally in 2024, reaching 11.7% positivity in late March. In 2025, the peak was lower, at 7.15% in late April. As of February 21, 2026, the highest positivity rate recorded this year is 6.1%. While these numbers provide a snapshot of the virus’s prevalence, it’s essential to note that wastewater surveillance data is just one piece of the puzzle. It’s complemented by clinical testing and hospital surveillance data to provide a more comprehensive picture of the situation.
Symptoms, Complications, and Treatment
The symptoms of HMPV are often similar to those of a common cold, making it demanding to distinguish from other respiratory viruses. Common symptoms include cough, fever, runny nose, and sore throat. However, in some cases, HMPV can lead to more serious complications, such as asthma exacerbations, ear infections, croup (a barking cough), bronchitis, and even pneumonia. Individuals at higher risk of severe illness include young children, older adults, and those with weakened immune systems or chronic medical conditions.
Currently, there is no specific antiviral medication to treat HMPV infections. Treatment focuses on supportive care, which includes rest, fluids, and over-the-counter medications to relieve symptoms. In severe cases, hospitalization may be necessary to provide respiratory support and manage complications. It’s crucial to consult a healthcare professional if symptoms worsen or if you belong to a high-risk group.
Preventing the Spread of HMPV
Preventing the spread of HMPV involves practicing good hygiene and taking steps to minimize exposure to the virus. These measures are similar to those recommended for preventing the spread of other respiratory illnesses, such as influenza and COVID-19. Key preventative measures include:
- Washing hands frequently with soap and water.
- Using an alcohol-based hand sanitizer when soap and water are not available.
- Cleaning and disinfecting frequently touched surfaces.
- Improving ventilation in indoor spaces.
- Avoiding close contact with sick individuals.
- Avoiding touching your eyes, nose, and mouth.
These simple steps can significantly reduce the risk of infection and help to protect vulnerable populations. Public health officials emphasize the importance of staying home when sick to prevent further spread of the virus.
Looking Ahead
While the current surge in HMPV cases is concerning, health officials emphasize that it is not a cause for panic. The virus is well-known, and while there is no vaccine, the focus remains on symptom management and protecting those most vulnerable. Continued wastewater surveillance will be critical in monitoring the virus’s trajectory and informing public health responses. The situation highlights the importance of ongoing investment in public health infrastructure and preparedness for emerging infectious diseases.
The California Department of Public Health is continuing to monitor HMPV activity closely and will provide updates as needed. Individuals can find more information about HMPV and other respiratory illnesses on the CDC website: https://www.cdc.gov/. The next update from the California Department of Public Health regarding HMPV is scheduled for March 23, 2026. We encourage readers to share this information with their communities and to prioritize preventative measures to protect themselves and others.