Researchers say COVID-19 omicron variant levels ‘low’ in Merced wastewater samples

The team of scientists who found evidence of COVID-19’s omicron variant in Merced’s wastewater say the levels they’ve measured are relatively low — though it’s still unclear how many local residents may be infected with the strain.

The research team from the Sewer Coronavirus Alert Network (SCAN) tested Merced’s municipal sewer system in recent weeks.

When they tested wastewater samples taken from Merced’s sewers, they found the omicron variant at lower levels than the delta variant, said Krista Wigginton, University of Michigan associate professor of civil and environmental engineering.

“They’re just kind of above the threshold of what we can detect, so most of the signal is still coming from the delta variant,” Wigginton said.

SCAN tests 12 sites in California, and analyzes the results daily before posting them within 24 hours.

COVID-19 variants are excreted in feces, Wigginton explained, and the wastewater allows researchers the chance to detect how many people per 100,000 have the variant.

Despite the variant being detected in Merced’s wastewater, it’s difficult for researchers to connect that to any confirmed cases in the city or county.

Merced County Department of Public Health thus far hasn’t publicly reported any confirmed cases of omicron. Officials could not be reached for comment Wednesday morning.

“We can’t say how many,” Wigginton said. “We’re not confident saying how many, but we’re confident in saying somebody in the Merced sewer shed who used a toilet had omicron.”

As of Tuesday, there were 26 active COVID-19 hospitalizations in the county and 684 total deaths since the initial outbreak in March 2020.

About 47.87% of Merced County’s 265,298 residents are fully vaccinated against the coronavirus — that’s 55.57% of the population of eligible residents age 5 and up.

The county confirmed 45,961 residents have been infected with the virus at some point since the start of the pandemic.

U.S. health officials have said that while the omicron variant of the coronavirus is rapidly spreading throughout the country, early indications suggest it may be less dangerous than delta, which continues to drive a surge of hospitalizations.

Samples tested statewide

Merced is one of several cities that’s part of the Sewer Coronavirus Alert Network and has local sewers tested.

Other cities in the network include Davis, Gilroy, Los Angeles, Modesto, Palo Alto, Paso Robles, San Diego, San Francisco and San Luis Obispo, along with 35 other cities, universities, water districts, sanitation districts and other utility districts.

The Sacramento Regional County Sanitation District is also part of the network. Researchers also said they found traces of the omicron variant in wastewater samples from Sacramento.

Wastewater testing is gaining popularity in other parts of the country and the world. Researchers at the University of Arizona tested wastewater samples in Pima County, Arizona, and the U.K.’s N-WESP network tests samples collected from the sewers of Britain’s towns and cities.

“We call it wastewater-based epidemiology,” Wigginton said. “It’s where we look to wastewater to find out what diseases are circulating and how much. It’s been used in the past, in a limited way, to understand where outbreaks of polio are happening, but this global approach to it that’s going on now with COVID, that’s unique and it’s really exciting.”