Wastewater Testing

Environmental monitoring of wastewater (regularly testing sewage) is another tool Healthy Davis Together is using to learn about COVID-19 and opportunities to prevent its spread in our community.

Did you know that the virus that causes COVID-19 (SARS-CoV-2) is found in the excrement (feces and urine) of individuals who have COVID-19, including asymptomatic and pre-symptomatic individuals? Wastewater testing can be used as an early warning detection system for the virus in a regional area (e.g., neighborhood) so that action can be taken to provide support and reduce the spread.

Healthy Davis Together (HDT) wastewater testing can help slow and prevent the spread of COVID-19 in two ways. First, it’s an inexpensive way to get information on city-wide infection trends over time. Trend data indicate whether existing efforts to combat COVID-19 are working and whether more needs to be done. Second, wastewater testing can identify areas where COVID-19 might be on the rise and therefore where we can put additional focus on direct support like free testing and quarantine support.

Through HDT, UC­ Davis and the City’s Department of Public Works have set up wastewater sample collection locations at seven key points (“nodes”) in the City’s sewage (“wastewater”) collection system. These nodes also draw directly from the City’s Wastewater Treatment Plant (WWTP). Each node pools the wastewater from a broad geographic region of the City (illustrated in the map below; note that some regions overlap), while the WWTP pools all city wastewater. This type of sampling provides a regional overview but does not isolate individual households. The HDT wastewater monitoring team is adding more samplers to capture the residential regions served by the city wastewater collection system.

How to read regional wastewater graphs
After collection, wastewater samples are analyzed in a UC Davis lab to determine the concentration of virus copies present. Concentration data are normalized (to adjust for things like rainfall and other factors that could affect the sample dilution) and plotted against the City’s Wastewater Treatment Plant numbers (the city-wide average). By comparing regional data (in blue) to the city-wide average (in green), we can see how peaks and valleys compare. The regional wastewater graphs will be updated every Saturday.

Health Davis Together encourages everyone to remain vigilant and follow guidance to prevent the spread of COVID-19 and all its variants, including:

• Wearing a mask/face covering; making sure it fits properly
• Keeping physical distance; at least 6 feet apart and more if possible
• Practicing good hand hygiene
• Getting tested at least weekly for COVID-19; even if you are asymptomatic
• Avoiding crowds and indoor gatherings
• Staying home if you feel sick
• Getting vaccinated when a vaccine is available to you

Wastewater testing is just one of the many tools and resources that can help keep Davis healthy. To learn more about wastewater surveillance as a strategy for containing COVID-19, please visit the Centers for Disease Control and Prevention (CDC)’s webpage on the topic. If you have questions, please email wastewater@HealthyDavisTogether.org.