SF wastewater levels show increasing concentrations of COVID-19

COVID-19 is on the rise again in the Bay Area, and San Francisco wastewater samples show that concentrations of the virus are at higher levels this year than at this time in 2023.

Amanda Bidwell of Stanford University’s WastewaterSCAN project said the current levels of COVID-19 in wastewater samples collected from sites across the Bay Area are elevated compared with those found in summer 2022.

“In summer 2023, we saw wastewater concentrations for SARS-CoV-2 start to increase in mid-June and peak during August,” she told The Examiner on Monday. “Wastewater levels are approaching those last seen in December 2023 and January 2024.”

Wastewater samples became a go-to method of tracking the COVID-19 virus during the pandemic to better assess viral levels in a community population.

Dr. Peter Chin-Hong, an infectious disease expert at UCSF, said several factors contributed to this season’s early spike in the virus.

“It’s been about six months since a lot of people got infected last time,” he said. “Immunity wanes after about six months. It doesn’t mean it goes away, but it’s just easier to be infected again.”

The latest family of variants — known as “FLiRT” and consisting of KP.1.1, KP.2 and KP.3 — has also contributed to the increase in cases, he said.

“They are just a little bit different from the last one, which was JN.1 over the winter,” Chin-Hong said. “Even though they’re not too different from the last ones, they’re different enough to be more transmissible.”

The City collects samples at the Oceanside Treatment Plant and Southeast Water Pollution Control Plant. The latest data from WastewaterSCAN found that JN.1 is still the dominant variant at the Oceanside site (37.5%), followed by KP.2 (22.4%). But at the Southeast site, KP.2 was the slightly more dominant variant (33.7%) over JN.1 (32%).

Finally, the increased number of people coming together in the last month or so — for events such as family celebrations, graduations and summer parties — has also contributed to the rise in cases.

“It’s happening about a month earlier,” Chin-Hong said. “It could be just the range of where the virus hits every year is not exactly the same, or it could be that fewer people are immunized in general, including in the Bay Area.”

As immunity wanes, people who are older and immunocompromised should take precautions, Chin-Hong said. Those who are eligible should get vaccinated sooner rather than later, and not wait for the new vaccine that’s coming out in the fall that will be based on the FLiRT variants, he said.

Overall, the concentration of COVID-19 is on the rise at more than half of the sites in the Bay Area that Wastewater SCAN collects samples from, Bidwell said.

In the last 21 days, the virus has been detected in 100% of the samples collected, she said, and 42% of the sites in the Bay Area are currently at high levels.

California has seen an increase in test positivity for COVID-19 in the last week of nearly 2% , according to the latest data from the California Department of Public Health. The rest of the country is lagging behind, according to the Centers for Disease Control and Prevention’s test-positivity tracker .

“[COVID-19] has to start off somewhere first,” Chin-Hong said. “Maybe we’ve already reached the peak in the Bay Area because we started off early. Who knows?”