Human metapneumovirus surges in San Francisco County, experts warn

Redwood City, San Francisco and Novato are among Bay Area communities showing high concentrations of human metapneumovirus, or HMPV, in public wastewater monitoring, prompting infectious-disease specialists to warn residents to take precautions as the region moves through the typical HMPV season. WastewaterSCAN dashboard data referenced by regional experts show elevated signals in San Francisco, Marin County, Vallejo, Napa, Novato, Santa Rosa, Sacramento and Davis, with Redwood City flagged as reporting the highest levels in the Bay Area.

City-level trends identified between mid-December and the end of February included increases in Merced, Novato and Sunnyvale, while Los Angeles County has shown low-to-moderate wastewater detections, according to the same surveillance mapping. Nationally, the WastewaterSCAN mapping and CDC trend data indicate higher HMPV activity across parts of the Midwest and Northeast, and multiple public datasets show a national rise in cases that began in October 2025.

Clinically, HMPV typically causes cough, fever and nasal congestion; infections usually last a few days to a week. Dr. David Weber, professor and medical director of infectious diseases at UNC Health, said, "The major symptoms are cough, running nose, fever. It's also prone to give you some wheezing, particularly if you have underlying asthma." Pediatric cases can include bronchiolitis and croup, with the Mayo Clinic describing croup's "barking" cough as similar to a seal barking.

There is no vaccine or specific antiviral therapy for HMPV, and care is primarily supportive. National reporting has noted that severe cases, particularly among young children and adults 65 and older, can require oxygen therapy. National surveillance previously recorded a notable surge in April 2025 when HMPV accounted for over 7 percent of weekly positive respiratory virus tests, a figure reported in national coverage of the 2025 surge.

Local infectious-disease experts emphasize seasonality and caution rather than alarm. Dr. Jessica August, chief of infectious diseases at Kaiser Permanente Santa Rosa, said, "Human metapneumovirus cases commonly start showing up in January before peaking in March or April and then tailing off in June." Public-health messaging reflected in regional analysis states, "A respiratory virus that doesn't have a vaccine or a specific treatment regimen is spreading in some parts of California — but there's no need to sound the alarm just yet, public health officials say."

Preventive measures recommended by experts and surveillance summaries include handwashing, avoiding contact with sick people and improving indoor ventilation. One expert identified only by the surname Gandhi noted that, because HMPV is an RNA virus that typically thrives in cold environments, "as people crowd together indoors, the virus spreads much more rapidly," while California's mild weather can aid ventilation.

Wastewater surveillance serves as an early community indicator but does not equate to lab-confirmed case counts or hospitalization totals; local public-health agencies and hospital systems in San Francisco County will need to confirm any clinical uptick. For now, Bay Area clinicians and public-health officials are urging measured vigilance as the region enters HMPV's expected seasonal peak.