Healthy Davis Together

Working to prevent the spread of COVID-19 in our community

Neighborhood Wastewater Data

Learn more about
our wastewater program

HDT Wastewater region map
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About Wastewaster Testing

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

The virus that causes COVID-19 (SARS-CoV-2) is found in the excrement (feces) of individuals who have COVID-19, including asymptomatic and pre-symptomatic individuals. This means that wastewater testing can be used as an early-warning detection system for the virus in a regional area (e.g., a neighborhood).

Healthy Davis Together (HDT) wastewater testing is helping to slow and prevent the spread and reemergence of COVID-19 in Davis in two ways. First, wastewater data can be used to strengthen confidence in clinical-testing data. When wastewater and clinical data don’t match, it can be a sign that clinical testing needs to be ramped up. Second, wastewater testing is an inexpensive way to get information on regional infection trends over time. Trend data indicate whether existing efforts to combat COVID-19 are working and whether more needs to be done in certain areas.

Davis Regional Testing Graphs

Wastewater sampling week of Jan. 17

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 site-specific data (in blue) to the city-wide average (in yellow), we can see how trends compare: whether the detectable amount of virus in a sampling zone is going up, going down, or staying about the same. These plots are updated every Saturday.

Technical notes:

  • Virus copy concentration represents an average of the detected concentrations of the N1 and N2 regions of the SARS-CoV-2 genome.
  • To visualize the data, we truncate outliers at the [1,99] percentile levels, calculate a two-week moving average, and apply a smoothed linear fit on the moving average to achieve a trendline.
  • In early March 2020, the sample-processing method was changed from ultrafiltration-based concentration and column-based manual extraction to automated concentration and extraction using magnetic particles.
  • In early September 2020, the sample-analysis method was changed from quantitative polymerase chain reaction (qPCR) to digital droplet polymerase chain reaction (ddPCR). Technical challenges associated with the methods switch resulted in lost data from early September to early October.

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For general information about Healthy Davis Together, please email [email protected].

For clinical question and general information, please contact 530-754-TEST. Representatives will be available to answer clinical question everyday from 9 a.m. to 5 p.m. and available to provide general information Monday – Friday from 9 a.m. to 5 p.m.