Wastewater testing sites across the Bay Area are picking up a growing signal of enterovirus D68, a seasonal virus most notorious for its rare ability to trigger a polio-like paralysis in small children. Detection levels are described as high and continuing to climb in Palo Alto, Napa, southeast San Francisco and San Rafael, according to the virus's typical late-summer-to-early-fall pattern.
The local uptick tracks a much larger national surge. As reported by The Independent, wastewater monitoring network WastewaterSCAN, which tracks traces of viruses in municipal sewage, found the virus in roughly 72% of national samples collected in September, a jump from just 20% in August, according to an October 2 update reported by Bay Area Telegraph. That spike pushed the pathogen to a “high” national classification, giving Bay Area families a clearer sense of just how widespread the current wave has become.
Enterovirus D68 is one of more than 100 non-polio enteroviruses circulating in the United States, and for most people it causes a cold-like illness — cough, shortness of breath and wheezing. Children infected with the virus may develop fever, difficulty breathing or pneumonia, according to the CDC. Infants, children and teenagers can be more seriously affected because they may lack immunity built up from previous exposure to the virus.
A Rare but Serious Complication
The condition drawing the most concern is acute flaccid myelitis, or AFM — an uncommon but dangerous neurological condition that mainly affects children. Symptoms typically appear several weeks after an enterovirus D68 infection and can include arm or leg weakness, loss of muscle tone and reflexes, pain, difficulty swallowing, slurred speech, difficulty moving the eyes, or facial droop or weakness.
The virus isn't new to California. It was first isolated by public health researchers in the state back in 1962, remaining an infrequently detected pathogen for decades before evolving into the larger outbreak strains that began appearing in the 2010s, per SFGATE. The first major U.S. epidemic hit in 2014, when federal public health laboratories confirmed 1,116 cases of severe respiratory illness across 47 states and Washington, D.C., with many hospitalized children requiring mechanical ventilation, according to the CDC.
Despite that history, AFM itself has remained rare. Since standardized national tracking began in August 2014, the CDC has recorded 800 confirmed AFM cases nationwide as of September 3, 2026, with peak years in 2014, 2016 and 2018. Over 90% of reported AFM cases occur in young children, with a historical median age of onset between 4 and 7 years old — one reason pediatricians and parents of young kids remain the primary audience for public health warnings on this virus.
Why Case Counts Don't Tell the Whole Story
Enterovirus D68 itself is not a nationally reportable disease, meaning local and state health departments aren't required to track routine clinical cases or deaths tied to it. That's part of why wastewater data, rather than emergency room counts, has become the primary early warning tool for tracking its spread. Suspected AFM cases are treated differently: public health regulations across states and territories require providers to immediately report any suspected Patients Under Investigation for the condition to local health departments, per CDC guidance.
The California Department of Public Health issued a health advisory this past July reminding clinicians to stay alert for EV-D68 respiratory illness and potential AFM cases during the late-summer and early-fall window, while recommending poliovirus stool testing to rule out other paralytic causes, according to Napa County health alerts. Notably, CDC epidemiological data from 2020 through 2025 show annual AFM cases have stayed low, between 17 and 48 per year, even during substantial EV-D68 respiratory surges in 2022 and 2024 — leaving researchers still investigating why recent circulating strains haven't translated into more neurological complications.
Older adults, small children and immunocompromised people are considered at greatest risk of severe illness from the virus. Dr. Monica Gandhi said respiratory illnesses can be severe for certain risk groups, underscoring why vigilance matters even as overall AFM numbers stay low.
Asthma and Other Risk Factors
One group deserves particular attention: kids with asthma. A CDC-led multicenter study published in JAMA Network Open found that among children hospitalized with EV-D68 respiratory illness, 37.1% had a pre-existing diagnosis of asthma or reactive airway disease, according to CIDRAP. That makes early medical evaluation especially important for families with asthmatic children during this surge.
There's no vaccine for enterovirus D68. The most effective protections remain familiar ones: frequently washing hands and avoiding contact with sick people. Bay Area residents are also being encouraged to get updated flu shots and COVID-19 vaccines this fall.
The timing adds urgency. The San Francisco Department of Public Health announced the city's first flu-related death of the season on October 1. Dr. Susan Philip said respiratory viruses such as flu and COVID should be taken very seriously, especially for people at higher risk of getting sick, adding that vaccines help people stay healthy and participate in fall festivities.
