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COVID-19 Wastewater surveillance

CDPH Wastewater Surveillance Network Dashboard

This dashboard provides an overview of ​wastewater surveillance of SARS-CoV-2 in California, with wastewater samples collected and analyzed by CDPH, wastewater utilities, and academic, laboratory, and other partners across the state (Cal-SuWers Network). 

The dashboard includes maps displaying outlines of each participating wastewater treatment plant service area (aka sewersheds). These areas represent the wastewater collection areas for each respective treatment plant and show where wastewater is being monitored for SARS-CoV-2 within the Cal-SuWers Network across California. For each sewershed, the dashboard also shows the levels of SARS-CoV-2 found, over time.


This dashboard is updated daily, Monday–Friday as new data are available, by 5:30pm. 

Note: Wastewater utilities typically collect samples on Sunday, Monday and Wednesday. Utilities in turn ship the samples to the laboratory the next day (+1–2 days), and it takes some time (+1–3 days) for the lab to process the sample and submit that data to our team. Ultimately the turnaround is typically 3–6 days from when samples are collected to when the results appears on this dashboard.

For questions about this project, data, or dashboard, please contact the CDPH Wastewater Surveillance Team at wws@cdph.ca.gov 


For data from WastewaterSCAN – content on this site is licensed under CC BY-NC 4.0.  All results are understood to be based on inputs that are experimental in nature, and are not intended to diagnose or treat any disease. The results are provided “as is” and without warranty of any kind. Stanford is not liable for any claim arising out of or in connection with the disclosure of these results. By accessing or copying any part of the database, the user accepts the terms of this license. Anyone seeking to use the database for other purposes or for research is required to contact Alexandria Boehm (aboehm@stanford.edu).​ For additional information please visit the WastewaterSCAN we​bpage​.​


Instructions for using this dashboard:

​​​ ​1. Select the sewershed site from the “1. Select Sewershed” filter (top right)

  • ​​Once a sewershed is selected, two reactive maps will display:
    1. “Overall Sewershed Site Locations” (left side) will highlight the sewershed location within the overall California region, and
    2. “Sewershed: [Sewershed Label]” (right side) will display a zoomed-in map of the sewershed with its geographic boundaries. Sewershed Label is generally formatted as: County (City or Treatment Plant name)
  • ​​​​​Note: only one sewershed can be selected

​​​​2. Select a single data source from the “2. Select Data Source” drop-down filter (top right)

  • Some sewersheds may have wastewater data that was analyzed by multiple laboratories.
  • These include: CDPH Drinking Water and Radiation Lab (DWRL), CDPH NWSS analyzed by UC Berkeley, WastewaterSCAN, Healthy Central Valley Together (HCVT), CDPH NWSS Commercial Contract (Biobot, LuminUltra).
  • Note: only one data source can be selected.

 3​. Select the range of dates using “3. Select Sample Date” filter (middle right)

  • Use the slider tool to select a desired date range.
  • Date range selectable is from December 16, 2020 to present day; however data first became available for different sites and laboratories at different times.
  • Note: selecting the date range will adjust the SARS-CoV-2 Concentrations graph (y-axis).

4. View result​s “SARS-CoV-2 Concentrations” (bottom image)

  • After completing the three filters above (steps 1–3), the “SARS-CoV-2 Concentrations” graph (bottom image) will display a plot of wastewater concentrations, with site selected in the main title (sewershed label).
  • The “Concentration Unit” (located above the graph) shows the units of the SARS-CoV-2 concentra tion plotted on the y-axis: “SARS-CoV-2/PMMoV” indicates SARS-CoV-2 concentrations that are normalized by a human fecal indicator called Pepper Mild Mottle Virus (PMMoV), and “copies/L wastewater” indicates raw SARS-CoV-2 concentrations in wastewater (see Details below).
  • The selected “Data Source” laboratory is indicated.
  • Points represent individual sample results. Line represents an average of the concentrations of all samples that fall within 10 days of that date (center aligned).

To view another sewershed, select the sewershed on the first filter (top right side) again along with all other filter criteria of “Data Source” and “Sample Date.”


Additional features:

Adjust the Overall Sewershed Site Location map to see more of the map

  • To zoom in/out, scroll on the map.
  • To move the view, click on the map and drag the cursor to desired location.
​To view an accessible version of data used in the CDPH Wastewater Surveillance Network Dashboard, download the Skip to main contentCDPH Wastewater Surveillance Network Dashboard Accessible Data Excel (CSV) file.​




Details

By selecting a sewershed (which includes the wastewater treatment plant service areas), you can see the SARS-CoV-2 RNA concentrations in wastewater for that location over time. Information about where the wastewater samples are taken are displayed at the top of the graph, as are details about which Cal-SuWers Network partner is contributing the data.

The x-axis represents the date of sample collection (the day the wastewater samples were collected from the site). The y-axis represents the SARS-CoV-2 concentration or amount of virus present per sample. As different laboratory and sample collection methodologies are used at different sites, “wastewater concentration” represents a different measurement at different locations, and absolute values are not displayed. See details about what is being measured underneath the location name at the top of the graph. Because different methodologies are used at different sites, direct comparisons of wastewater concentration values from different locations are discouraged.

As of July 5, 2022, SARS-CoV-2 concentrations for DWRL are now reported as normalized to a human fecal indicator, rather than raw SARS-CoV-2 concentrations. Currently, the human fecal indicator being measured at our contributing laboratories is Pepper Mild Mottle virus (PMMoV), a plant RNA virus that is abundant in human feces and rarely found in animal feces. This plant virus can be found in the diets of most healthy human populations and is considered a reliable indicator for the presence of human feces in a wastewater sample.1 Human fecal indicators are measured to provide insight into the number of people contributing to a sewershed at any given time, and human fecal normalization may allow for clearer interpretation of SARS-CoV-2 concentrations.2

CDPH analyses of DWRL wastewater data show improved correlation with case incidence rates after normalization to PMMoV (SARS-CoV-2/PMMoV), as compared to raw SARS-CoV-2 (copies/L wastewater) data. Additionally, our SCAN partner laboratory had similar findings and their data is presented as normalized to PMMoV. However, other contributing laboratories prefer raw concentrations to be reported, as they either do not measure PMMoV or have not found an improvement with normalization. As such, whether raw or normalized concentrations are reported varies from laboratory to laboratory. Description of whether a normalized or raw concentration is presented is located in text at the top of the concentration graph (“Concentration Unit”).

The full dataset, containing raw concentrations for all data sources, can be accessed from the California Open Data Portal. Normalized data can be manually calculated – if desired – by the following equation in the California Open Data Portal dataset:

Equation: PMMoV normalized concentration = (pcr_target_avg_conc)/(hum_frac_mic_conc)

The dots on the graph display the average concentration for all wastewater samples collected on that date. The line represents a 10-day rolling average of the wastewater data. The 10-day rolling average is added to help guide the eye to trends in the data. 

Guide to CalSuWers Graph

(click image to enlarge)

Cal-SuWers Graph Guide (PDF)

Data Limitations:

Wastewater surveillance for viral detection is still a developing field. Below are some important considerations to keep in mind. 

  • It is not possible to reliably and accurately predict the total number of infected individuals in a community based on sewage surveillance alone.
  • Wastewater surveillance will not represent homes on septic-based systems.
  • Community-level wastewater surveillance at a wastewater treatment plant will not represent communities or facilities served by decentralized systems, such as prisons, universities, or hospitals that treat their own sewage.
  • Low levels of infection in a community may not be captured by sewage surveillance if the quantity of SARS-CoV-2 falls below the limit of detection for laboratory analysis.
  • Wastewater is a complex environmental sample and inherent variability in measured concentrations are expected due to environmental variability, day-to-day differences in sewershed and population dynamics, and laboratory variability. As such, trends (>3 data points) are more reliable than individual data points; concentration of any individual data point may reflect variability and should be interpreted in appropriate context and with caution.

References

  1. Kitajima, M., Sassi, H.P. & Torrey, J.R. Pepper mild mottle virus as a water quality indicator. npj Clean Water 1, 19 (2018). https://doi.org/10.1038/s41545-018-0019-5
  2. Centers for Disease Control and Prevention (2022). Wastewater Surveillance Testing Methods. https://www.cdc.gov/healthywater/surveillance/wastewater-surveillance/testing-methods.html. Accessed July 11, 2022.
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