SAN DIEGO COUNTY, Calif. — An "unprecedented" spike in COVID-19 viral load in wastewater collected from San Diego County's primary wastewater treatment facility was reported Saturday by UC San Diego School of Medicine researchers.
The amount of COVID-19 virus detected in wastewater has predicted the region's COVID-19 caseload up to three weeks ahead of clinical diagnostic reports, the researchers said.
Since people with COVID-19 shed the virus in their stool even before they experience symptoms, wastewater screening acts as an early warning system.
"The wastewater screening results reported on Friday are unlike any the team has seen before," said Jackie Carr of UC San Diego Health. Both Delta and Omicron variants of the virus were detected in the wastewater.
"This confirms prior county reports that Omicron is already here and circulating in our community," said Dr. Wilma Wooten, San Diego County's public health officer.
"This is the steepest curve in viral load we've seen since we began screening wastewater in the summer of 2020, and it's continuing to get worse faster than ever before," said Rob Knight, professor and wastewater screening leader at UC San Diego School of Medicine.
Researchers and public health officials said they hoped the warning would encourage the local community to step up efforts to help mitigate the expected surge.
In addition to wearing face masks in indoor public spaces, as recently mandated by California, they urged people to get their vaccines or boosters if they haven't already.
They also recommended downloading the CA Notify exposure notification system to smartphones, limiting time spent indoors or unmasked with others, and taking steps to improve indoor ventilation and air filtration.
"In addition, every person in San Diego County needs to have a low threshold for testing right now," said Christopher Longhurst, chief medical officer and chief digital officer at UC San Diego Health. "Don't wait. If you feel the slightest symptoms, if you think you might have had contact with someone with COVID-19, if you've gathered in crowds without masks, if you're planning a get together -- test, test, test."
COVID-19 PCR tests are available at UC San Diego Health, various San Diego County sites, other health providers and community pharmacies.
At-home rapid antigen tests are available from retail pharmacies and online vendors. Anyone who tests positive for COVID-19 should consult their health care provider.
San Diego County has only one primary wastewater treatment facility, in the Point Loma neighborhood. All excrement flushed away by nearly two-thirds of the county's residents, including those on the UC San Diego campus, ends up there.
UCSD researchers pick up wastewater samples that had been collected and stored for them by lab technicians at the treatment plant.
They bring the samples to a lab at the La Jolla campus to test them for the COVID-19 virus, along with wastewater samples collected from more than 350 campus buildings. All positive samples are sequenced to track viral variants.
The team can detect even a single infected, asymptomatic person living or working in a large building of more than 500 people on the UCSD campus.
They have found that notifying the occupants of each building with positive wastewater increases COVID-19 testing rates by as much as 13-fold. The approach has enabled early detection of 85 percent of COVID-19 cases on UCSD's campus, officials said.
WATCH RELATED: San Diego County confirms first case of COVID-19 omicron variant (December 2021)