Informing Public Health Across Merced County
Dr. Salvador Sandoval is the County Health Officer for Merced County in California’s Central Valley. Among the 290,000 residents that reside in Merced County, 46,000 live in Los Banos, located on the east side of the county. In early April of 2023, Sandoval watched in concern as COVID-19 levels in Los Banos spiked to more than 10 times the month before. Yet, in the city of Merced, on the county’s west side, COVID-19 rates had dipped to their lowest point of the year for its 86,000 residents.
In the early days of the pandemic, such precise insights were unavailable. Only a couple years later, Dr. Sandoval now enjoys near real-time tracking of COVID-19, flu, RSV and numerous other infectious diseases through Healthy Central Valley Together (HCVT). HCVT aims to increase access to infectious disease data using wastewater monitoring in rural and disadvantaged areas in Central California, especially in smaller counties like Merced that have limited or no in-house lab services. HCVT partners with WastewaterSCAN to monitor wastewater for infectious diseases.
Seeing the troubling spike in Los Banos, within hours Dr. Sandoval was able to notify hospitals and urgent care providers in the area to be on the lookout for new cases. He attributed Los Banos’ commuter population traveling to San Jose and the Bay Area for work, for the increased risk of exposure to COVID-19 and the disparity in COVID-19 infection rates in the two communities.
“People were starting to think that the pandemic was over, and we let them know to keep their eyes open,” Sandoval said. “We were able to emphasize treatment with Paxlovid and that being vaccinated didn’t mean someone shouldn’t seek treatment.”
Such city-by-city precision epidemiology is possible because Merced and Los Banos are served by separate wastewater treatment plants that are both a part of HCVT and WastewaterSCAN. With a small sample from each plant several times a week, Dr. Sandoval can track virus levels across several communities at once and monitor trends via the HCVT website and WastewaterSCAN’s data dashboard. He knows when rates are rising or falling—indicating the relative number of people infected in a specific location.
Dr. Sandoval’s story is only one among many about the ways wastewater data has become integral to his public health team. Before HCVT, the team relied primarily on clinical data—PCR testing and hospital admissions—which can lag infections by days to weeks and omits asymptomatic carriers who don’t get tested or seek treatment.
“I was really worried when we didn’t have reliable test results from the PCR tests. We just had to go with patterns – ‘Oh, the Bay Area is getting hit hard; now we’re next,’” Sandoval explains of his expanded insights and capabilities made possible by HCVT.
Nonetheless, while wastewater data is a powerful new tool to help keep his residents healthy, Dr. Sandoval sees it as a complement, not a replacement for, the familiar clinical data he still uses on a daily basis.
Dr. Sandoval speaks highly of the newfound and comprehensive view that wastewater data provides across a range of diseases threatening local communities. A jump in any one infection might trigger a similar response to those in Los Banos in the spring of 2023 – such as, heightened alerts to the health community when influenza season kicks in, a public awareness campaign to highlight symptoms when norovirus levels are on the rise, outreach to high-risk nursing homes, shelters for the unhoused, and health facilities when RSV is looming.
Wastewater monitoring has become a critical tool in Dr. Sandoval’s arsenal to combat infectious disease in Merced County. It has helped override data limitations that many smaller counties like Merced face for COVID-19 and beyond. It is fast. It is precise. And it is community wide.
“Everyone has to go to the bathroom,” Sandoval says. “So, you’re going to get the data.”