California health officials are monitoring an increase in human metapneumovirus (HMPV), a common respiratory virus, detected in wastewater across several communities. While the rise is notable, experts emphasize there’s no cause for widespread alarm, particularly as immunity levels have begun to recover following the disruptions of the COVID-19 pandemic. The virus, which doesn’t have a specific vaccine or treatment, is currently being observed at varying levels throughout the state, with higher concentrations reported in Northern California.
Data from the WastewaterScan Dashboard, a public database tracking infectious diseases through sewage monitoring, indicates a majority of Northern California communities are experiencing high levels of HMPV. A Los Angeles Times analysis further pinpointed increases in HMPV levels in Merced, located in the San Joaquin Valley and the Bay Area cities of Novato and Sunnyvale between mid-December and the complete of February. Los Angeles County has similarly detected the virus, though currently at low to moderate levels. Understanding this resurgence of HMPV is key, as it signals a potential return to pre-pandemic patterns of seasonal respiratory illnesses.
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. Dr. Neha Nanda, chief of infectious diseases and hospital epidemiologist for Keck Medicine of USC, explained the transmission pathways. Like influenza, HMPV thrives and spreads more easily in colder temperatures, infectious disease experts note. Typically, HMPV cases begin appearing in January, peaking in March or April, and declining by June, as observed by Dr. Jessica August, chief of infectious diseases at Kaiser Permanente Santa Rosa.
Why the Recent Increase?
Prior to the 2020 pandemic, regular seasonal exposure to viruses like HMPV helped build a degree of natural immunity within the population. This immunity waned as public health measures – such as social distancing and mask-wearing – reduced transmission. As people resumed normal activities, they became more susceptible to the virus. Notably, there is currently no vaccine available for human metapneumovirus. “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,” Dr. August said. “All of that also led to longer viral seasons, more severe illness. But all of these things have settled down in many respects.”
National surveillance data reflects this trend. 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 saw a peak of 7.15% in late April. As of February 21, 2026 – the most recent date with complete data – the highest test positivity rate recorded this year was 6.1%.
Symptoms and Treatment
Most individuals infected with HMPV experience mild, cold-like symptoms, including cough, fever, nasal congestion, and sore throat, and may not require medical attention. However, the infection can progress to more serious conditions, such as asthma attacks, reactive airway disease (wheezing and difficulty breathing), middle ear infections, croup (characterized by a “barking” cough), bronchitis, and even pneumonia. Individuals who are immunocompromised or have underlying medical conditions, as well as young children and older adults, are at higher risk of developing severe illness, Dr. Nanda cautioned.
Currently, there is no specific treatment protocol or antiviral medication for HMPV. Treatment typically focuses on managing symptoms, with recommendations for rest and increased fluid intake, according to the American Lung Association. If symptoms worsen, seeking medical advice is recommended.
Preventing HMPV Spread
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 move forward, continued monitoring of HMPV and other respiratory viruses will be crucial. Increased awareness and adherence to preventative measures can assist mitigate the impact of these illnesses on public health. The resurgence of HMPV serves as a reminder of the ongoing need for vigilance and proactive health practices.
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Disclaimer: This information is intended for general knowledge and informational purposes only, and does not constitute medical advice. This proves essential to consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.
