COVID-19 is making an unexpected resurgence in California, with San Francisco showing some of the highest levels of the virus detected in wastewater surveillance since the previous winter season. According to newly released data from the California Department of Public Health, the virus is present at moderate levels across most of the state, but certain areas, especially the Bay Area, are recording alarming spikes.
In San Francisco specifically, six out of nine wastewater testing sites reported high concentrations of the virus. Wastewater surveillance has become a key strategy for detecting early signs of viral spread. Unlike traditional testing methods that rely on symptomatic individuals seeking care, wastewater monitoring provides a broader picture by analyzing fragments of viral DNA and RNA excreted by both symptomatic and asymptomatic carriers. This helps health officials forecast upcoming surges before hospitals begin to see a rise in admissions.
Historically, respiratory illnesses like influenza tend to spread more easily during colder months when people spend more time indoors. However, COVID-19 has repeatedly defied seasonal expectations since the onset of the pandemic in 2020. It has shown a pattern of peaking not just during the winter, but also during the summer, as new variants emerge and circulate in the population. This year appears to follow the same trend, with data now indicating a possible early summer surge.
A major driver behind the current uptick is the rise of the NB.1.8.1 variant, informally known as “nimbus.” The U.S. Centers for Disease Control and Prevention recently published preliminary data confirming the growing prevalence of this strain. The variant has gained attention due to its distinctive symptom profile, most notably a severe and painful sore throat often described by patients as feeling like “razor blades.” In addition to throat pain, symptoms associated with COVID-19 continue to include fever, chills, fatigue, coughing, and body aches, similar to influenza.
Public health experts are urging caution, especially for those at elevated risk of developing serious complications from the virus. Older adults, people with underlying medical conditions, and immunocompromised individuals are considered particularly vulnerable. Physicians and infectious disease specialists continue to recommend booster shots to reduce the risk of severe illness. The newest COVID-19 booster is tailored to current circulating strains and offers renewed protection for those who may have waning immunity.
Health professionals emphasize the importance of basic hygiene practices as well. Regular handwashing, avoiding crowded indoor settings when ill, and wearing masks in high-risk environments are simple but effective measures to prevent transmission. Even for those not considered high-risk, reinfection or complications such as long COVID and potential impacts on pregnancy remain serious concerns. Medical providers strongly advise those uncertain about their eligibility for boosters or at-risk status to consult healthcare professionals.
The current situation highlights the ongoing unpredictability of COVID-19 and the need for continued vigilance. While vaccination rates and previous infections have built a level of community immunity, the emergence of new variants like nimbus demonstrates that the virus remains capable of disrupting public health. Surveillance systems like wastewater monitoring are crucial in helping public health agencies respond swiftly to outbreaks, and residents are encouraged to pay attention to local updates and guidance.
San Francisco’s high levels of viral detection in wastewater serve as a timely reminder that COVID-19 is far from gone. As California moves deeper into the summer months, health officials are monitoring developments closely and urging people to protect themselves and their communities. Staying updated on vaccination, practicing good hygiene, and being mindful of new variants will remain key strategies in navigating the ongoing presence of the virus.
