SARS-CoV-2 Wastewater Monitoring Data

The County of Santa Clara Public Health Department provides an overview of SARS-CoV-2 virus concentration in wastewater samples collected at wastewater treatment facilities that serve people in Santa Clara County. Four wastewater treatment facilities receive wastewater from designated geographic areas, known as “sewersheds”, within Santa Clara County. SARS-CoV-2 is the virus that causes COVID.

Monitoring concentrations of SARS-CoV-2 in wastewater can comprehensively detect levels of COVID infection within a community and track the prominence of new variants.

SARS-CoV-2 Wastewater Monitoring

Data is updated daily Monday through Friday, excluding holidays.

Source: Sewer Coronavirus Alert Network (SCAN) project by Stanford University
 

     

    • Select a sewershed of interest and click “Visit”. Select “All Sewersheds in Santa Clara County” to view all 4 sewersheds in one graph.
    • Select a time period of wastewater sample collection.

    When reviewing these graphs, it is important to look at the overall, sustained trends, instead of measurements on any given day. Wastewater samples tend to have some variability simply due to the nature of environmental samples.

     

    SARS-CoV-2 (the virus that causes COVID) is shed in feces by infected individuals and can be measured in wastewater. More cases of COVID in the community are associated with increased levels of SARS-CoV-2 in wastewater, meaning that data from wastewater analysis can be used as an indicator of the level of transmission of COVID in the community.

    • Wastewater monitoring provides a mechanism to monitor the level of community transmission as clinical testing declines, and other, more convenient testing takes place (such as home-based rapid antigen tests) that are not reported to the Public Health Department.
    • It can help confirm current trends of COVID-19 infections in the community that are based on clinical data.
    • Wastewater helps pinpoint areas in the county where the virus is more prevalent.
    • It includes asymptomatic individuals and people who are unable or unwilling to obtain clinical tests, for a variety of reasons.
    • Wastewater is available sooner than information from clinical testing, providing the public and health professionals with early signals as to whether COVID infections are increasing or decreasing within the community and if new variants are rising in prominence.

    Wastewater is one of a number of important data sources Public Health uses to monitor COVID in Santa Clara County. For more information, visit the County of Santa Clara COVID-19 Data and Reports Page.

     

    Wastewater samples are collected 7 days a week from all 4 wastewater treatment facilities within Santa Clara County. Results from the wastewater samples are available within 24 to 48 hours.

     

    The 4 wastewater treatment facilities collectively serve approximately 1,901,352 people, representing 98% of Santa Clara County’s total population.

    Wastewater samples are collected at the following wastewater treatment plants:

    Sewershed Wastewater treatment facility                                                                                                                                                                                                                                       Approximate number of people in Santa Clara County served
    San Jose San Jose-Santa Clara Regional Wastewater Facility 1,419,393
    Palo Alto Palo Alto Regional Water Quality Control Plant  215,544
    Sunnyvale Donald M. Somers Water Pollution Control Plant 161,021
    Gilroy South County Regional Wastewater Authority 105,394

    Source: U.S. Census Bureau, 2020 American Community Survey block data

    San Jose-Santa Clara Regional Wastewater Facility serves people in the cities of San Jose, Santa Clara and Milpitas; Cupertino Sanitary District (City of Cupertino and nearby unincorporated areas); West Valley Sanitation District (Cities of Campbell, Los Gatos, Monte Sereno, and Saratoga); County Sanitation District No. 2-3 (unincorporated area); and Burbank Sanitary District (unincorporated area).

    Palo Alto Regional Water Quality Control Plant serves people in Los Altos, Los Altos Hills, Mountain View, Palo Alto, Stanford University, and the East Palo Alto Sanitary District. Note: A portion of wastewater received at the Palo Alto Regional Water Quality Control Plant comes from San Mateo County.

    Donald M. Somers Water Pollution Control Plant serves people in the city of Sunnyvale; Rancho Rinconada portion of Cupertino; and Moffett Federal Airfield.

    South County Regional Wastewater Authority serves people in the cities of Gilroy and Morgan Hill.

     

    This table provides categorization as to whether current SARS-CoV-2 concentration levels within each sewershed are considered “high”, “medium”, or “low”. These categories are based on historical data of SARS-CoV-2 virus concentration in all four sewersheds during the Omicron (BA.1) surge from December 2021 to February 2022. Please note that these categorizations are meant to convey the level of transmission of COVID within the community and are not tied to automatic changes in policy or guidance.

    Category Distribution tertiles of population-weight Santa Clara County overall SARS-CoV-2 RNA concentration during Omicron surge Range of SARS-CoV-2 RNA concentration values (7-day trimmed avg. of N/PMMoV)
    LOW Lower tertile <= 0.0000566
    MEDIUM Middle tertile > 0.0000566 and <= 0.000257
    HIGH Upper tertile > 0.000257

     

    SARS-CoV-2 concentration was the highest between December 2021 to February 2022, as compared to any other time during the COVID pandemic. This period reflects the time in which the Omicron (BA.1) variant was the most predominant variant, and is referred to here as the “Omicron surge” period. Public Health is using Omicron surge concentration levels as a comparison point because this period reflects when COVID infections were most widespread.

     

    Protocol of Sample Collection & Testing: Samples for testing consist of “settled solids” from wastewater entering each treatment plant. Samples are collected 7 days a week from the wastewater treatment plants and are transported daily to a commercial lab for analysis. Laboratory staff process the samples to quantify pieces of the SARS-CoV-2 viral genome in the wastewater. These procedures use methods to concentrate solids and extract RNA and detect viral RNA. Results are typically ready within 24 hours of sample drop-off and are uploaded to this page. The quick turnaround and posting are one of the major advantages of utilizing this data.

    Interpretation of Plots: Data reflected in the table below shows the results for one SARS-CoV-2 gene (N gene), and the concentrations are “normalized” by the concentration of a plant virus that is harmless to humans but is shed in stool (pepper mild mottle virus, or PMMoV). Normalizing by PMMoV adjusts for changes in the amount of feces in the sample and the efficiency of the procedures from day to day.

    Wastewater typically contains waste from a variety of sources, such as from your shower or a commercial process. These types of waste do not have stool (which is the source of SARS-CoV-2) so they dilute the sample. Therefore, we adjust this sample to the known amount of feces in the wastewater to get an accurate result. 

    The curves displayed are the “7-day trimmed average” of the sample results. This is done by using 7 consecutive samples, eliminating the maximum and minimum among the 7 samples, and then taking the mean. The smoothing is right aligned. Trends in wastewater have been shown to track trends in COVID incidence. 

    The County of Santa Clara Public Health Department also provides wastewater monitoring data on influenza, or flu.

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