NOTICE: As of September 6, 2024, the wastewater surveillance dataset will now be hosted on: https://data.chhs.ca.gov/dataset/wastewater-surveillance-data-california. The dataset will no longer be updated on this webpage and will contain a historic dataset. Users who wish to access new and updated data will need to visit the new webpage.

The California Department of Public Health (CDPH) and the California State Water Resources Control Board (SWRCB) together are coordinating with several wastewater utilities, local health departments, universities, and laboratories in California on wastewater surveillance for SARS-CoV-2, the virus causing COVID-19. Data collected from this network of participants, called the California Surveillance of Wastewater Systems (Cal-SuWers) Network, are submitted to the U.S. Centers for Disease Control and Prevention (CDC) National Wastewater Surveillance System (NWSS).

During the COVID-19 pandemic, it has been used for the detection and quantification of SARS-CoV-2 virus shed into wastewater via feces of infected persons. Wastewater surveillance tracks ""pooled samples"" that reflect the overall disease activity for a community serviced by the wastewater treatment plant (an area known as a ""sewershed""), rather than tracking samples from individual people. Notably, while SARS-CoV-2 virus is shed fecally by infected persons, COVID-19 is spread primarily through the respiratory route, and there is no evidence to date that exposure to treated or untreated wastewater has led to infection with COVID-19.

Collecting and analyzing wastewater samples for the overall amount of SARS-CoV-2 viral particles present can help inform public health about the level of viral transmission within a community. Data from wastewater testing are not intended to replace existing COVID-19 surveillance systems, but are meant to complement them. While wastewater surveillance cannot determine the exact number of infected persons in the area being monitored, it can provide the overall trend of virus concentration within that community. With our local partners, the SWRCB and CDPH are currently monitoring and quantifying levels of SARS-CoV-2 at the headworks or ""influent"" of 21 wastewater treatment plants representing approximately 48% of California's population."

The California Department of Public Health (CDPH) is coordinating with wastewater utilities, local health departments, academic researchers, and laboratories in California on wastewater surveillance for infectious disease pathogens of interest to public health (such as SARS-CoV-2, the virus causing COVID-19, influenza, respiratory syncytial virus (RSV), mpox, and norovirus). Data collected from this network of participants, called the California Surveillance of Wastewaters (Cal-SuWers) Network, are submitted to the U.S. Centers for Disease Control and Prevention (CDC) National Wastewater Surveillance System (NWSS).

Collecting and analyzing wastewater samples for the presence of, and amount of (concentration), a specified pathogen target can help inform public health about circulation of that infectious disease within a community. Data from wastewater testing do not replace existing public health surveillance systems but complement them. While wastewater surveillance cannot determine the exact number of infected persons in the area being monitored, it can provide overall trends of pathogen concentration within that community.

Please note that data included in the Cal-SuWers Network and available here originate from multiple programs and laboratories. Methodologies for producing wastewater data are not currently standardized, and analyses, comparisons, and aggregations should be done with caution. Wastewater is a complex environmental sample and inherent variability in measured concentrations is expected due to environmental variability, day-to-day differences in sewershed and population dynamics, differences in the amount of shedding between people and pathogens, and laboratory and sampling variability. Please see the CDPH Cal-SuWers, CDC NWSS, and CDC Public Health interpretation and Use of Wastewater Surveillance data webpages for more information.

Historical wastewater data can be found here.

The California Department of Public Health (CDPH) aggregates confirmed cases of COVID-19 by sewershed restricted locations. Confirmed cases are defined as individuals with a positive molecular test, which tests for viral genetic material, such as a polymerase chain reaction test.

Since wastewater data available starts from January 1st, 2021, rather than the beginning of the COVID-19 pandemic in 2020, the cumulative counts of the confirmed cases variable are shown as “NA”.

Please note that values less than 5 for confirmed cases are masked (shown as “Masked”) if the sewershed population size is 50,000 or fewer, in accordance with de-identification guidelines. Values less than 3 for cases are masked (shown as “Masked”) if the sewershed population size is between 50,001 and 250,000. For no confirmed cases reported, values are set as zero.

The California Department of Public Health (CDPH) and the California State Water Resources Control Board (SWRCB) together are coordinating with several wastewater utilities, local health departments, universities, and laboratories in California on wastewater surveillance for SARS-CoV-2, the virus causing COVID-19. Data collected from this network of participants, called the California Surveillance of Wastewater Systems (Cal-SuWers) Network, are submitted to the U.S. Centers for Disease Control and Prevention (CDC) National Wastewater Surveillance System (NWSS).

Collecting and analyzing wastewater samples for the overall amount of SARS-CoV-2 viral particles present can help inform public health about the level of viral transmission within a community. Data from wastewater testing are not intended to replace existing COVID-19 surveillance systems, but are meant to complement them. While wastewater surveillance cannot determine the exact number of infected persons in the area being monitored, it can provide the overall trend of virus concentration within that community. With our local partners, the SWRCB and CDPH are currently monitoring and quantifying levels of SARS-CoV-2 at the headworks or ""influent"" of 21 wastewater treatment plants representing approximately 48% of California's population."

The COVID-19 pandemic has undoubtedly impacted everyone around the globe. In 2020, many countries entered into a lockdown, transforming daily lifestyles into isolation. The SARS-CoV-2 virus that causes the disease COVID-19 slowly spread to different regions of the world, and the first cases of COVID-19 infection in Los Angeles County, California, were documented in mid-January 2020. In March 2020, Governor Gavin Newsom of California declared a state of emergency and implemented a stay-at-home order (1). Therefore,

people were quarantined at home, and many “non- essential” businesses were closed, including schools.

With no cure available and hospitals reaching maximum capacity, scientists raced to develop vaccines to immunize individuals against the virus. Meanwhile, wastewater technicians began collecting wastewater samples to monitor the presence of the SARS-CoV-2 virus shed from infected residents. We hypothesized that the presence of SARS-CoV-2 RNA in LA County wastewater would decrease as localized vaccination rates increased. Here, we describe a meta-analysis comparing two data sets; the vaccination progression data in Los Angeles County, and the wastewater surveillance PCR

IntroductionOver a third of the communities (39%) in the Central Valley of California, a richly diverse and important agricultural region, are classified as disadvantaged—with inadequate access to healthcare, lower socio-economic status, and higher exposure to air and water pollution. The majority of racial and ethnic minorities are also at higher risk of COVID-19 infection, hospitalization, and death according to the Centers for Disease Control and Prevention. Healthy Central Valley Together established a wastewater-based disease surveillance (WDS) program that aims to achieve greater health equity in the region through partnership with Central Valley communities and the Sewer Coronavirus Alert Network. WDS offers a cost-effective strategy to monitor trends in SARS-CoV-2 community infection rates.MethodsIn this study, we evaluated correlations between public health and wastewater data (represented as SARS-CoV-2 target gene copies normalized by pepper mild mottle virus target gene copies) collected for three Central Valley communities over two periods of COVID-19 infection waves between October 2021 and September 2022. Public health data included clinical case counts at county and sewershed scales as well as COVID-19 hospitalization and intensive care unit admissions. Lag-adjusted hospitalization:wastewater ratios were also evaluated as a retrospective metric of disease severity and corollary to hospitalization:case ratios.ResultsConsistent with other studies, strong correlations were found between wastewater and public health data. However, a significant reduction in case:wastewater ratios was observed for all three communities from the first to the second wave of infections, decreasing from an average of 4.7 ± 1.4 over the first infection wave to 0.8 ± 0.4 over the second.DiscussionThe decline in case:wastewater ratios was likely due to reduced clinical testing availability and test seeking behavior, highlighting how WDS can fill data gaps associated with under-reporting of cases. Overall, the hospitalization:wastewater ratios remained more stable through the two waves of infections, averaging 0.5 ± 0.3 and 0.3 ± 0.4 over the first and second waves, respectively.

Introduction: Over a third of the communities (39%) in the Central Valley of California, a richly diverse and important agricultural region, are classified as disadvantaged—with inadequate access to healthcare, lower socio-economic status, and higher exposure to air and water pollution. The majority of racial and ethnic minorities are also at higher risk of COVID-19 infection, hospitalization, and death according to the Centers for Disease Control and Prevention. Healthy Central Valley Together established a wastewater-based disease surveillance (WDS) program that aims to achieve greater health equity in the region through partnership with Central Valley communities and the Sewer Coronavirus Alert Network. WDS offers a cost-effective strategy to monitor trends in SARS-CoV-2 community infection rates.

Methods: In this study, we evaluated correlations between public health and wastewater data (represented as SARS-CoV-2 target gene copies normalized by pepper mild mottle virus target gene copies) collected for three Central Valley communities over two periods of COVID-19 infection waves between October 2021 and September 2022. Public health data included clinical case counts at county and sewershed scales as well as COVID-19 hospitalization and intensive care unit admissions. Lag-adjusted hospitalization:wastewater ratios were also evaluated as a retrospective metric of disease severity and corollary to hospitalization:case ratios.

Results: Consistent with other studies, strong correlations were found between wastewater and public health data. However, a significant reduction in case:wastewater ratios was observed for all three communities from the first to the second wave of infections, decreasing from an average of 4.7 ± 1.4 over the first infection wave to 0.8 ± 0.4 over the second.

Discussion: The decline in case:wastewater ratios was likely due to reduced clinical testing availability and test seeking behavior, highlighting how WDS can fill data gaps associated with under-reporting of cases. Overall, the hospitalization:wastewater ratios remained more stable through the two waves of infections, averaging 0.5 ± 0.3 and 0.3 ± 0.4 over the first and second waves, respectively.

IntroductionOver a third of the communities (39%) in the Central Valley of California, a richly diverse and important agricultural region, are classified as disadvantaged—with inadequate access to healthcare, lower socio-economic status, and higher exposure to air and water pollution. The majority of racial and ethnic minorities are also at higher risk of COVID-19 infection, hospitalization, and death according to the Centers for Disease Control and Prevention. Healthy Central Valley Together established a wastewater-based disease surveillance (WDS) program that aims to achieve greater health equity in the region through partnership with Central Valley communities and the Sewer Coronavirus Alert Network. WDS offers a cost-effective strategy to monitor trends in SARS-CoV-2 community infection rates.MethodsIn this study, we evaluated correlations between public health and wastewater data (represented as SARS-CoV-2 target gene copies normalized by pepper mild mottle virus target gene copies) collected for three Central Valley communities over two periods of COVID-19 infection waves between October 2021 and September 2022. Public health data included clinical case counts at county and sewershed scales as well as COVID-19 hospitalization and intensive care unit admissions. Lag-adjusted hospitalization:wastewater ratios were also evaluated as a retrospective metric of disease severity and corollary to hospitalization:case ratios.ResultsConsistent with other studies, strong correlations were found between wastewater and public health data. However, a significant reduction in case:wastewater ratios was observed for all three communities from the first to the second wave of infections, decreasing from an average of 4.7 ± 1.4 over the first infection wave to 0.8 ± 0.4 over the second.DiscussionThe decline in case:wastewater ratios was likely due to reduced clinical testing availability and test seeking behavior, highlighting how WDS can fill data gaps associated with under-reporting of cases. Overall, the hospitalization:wastewater ratios remained more stable through the two waves of infections, averaging 0.5 ± 0.3 and 0.3 ± 0.4 over the first and second waves, respectively.

Data is from the California Department of Public Health (CDPH) Respiratory Virus Weekly Report. The report is updated each Friday. Laboratory surveillance data: California laboratories report SARS-CoV-2 test results to CDPH through electronic laboratory reporting. Los Angeles County SARS-CoV-2 lab data has a 7-day reporting lag. Test positivity is calculated using SARS-CoV-2 lab tests that has a specimen collection date reported during a given week. Laboratory surveillance for influenza, respiratory syncytial virus (RSV), and other respiratory viruses (parainfluenza types 1-4, human metapneumovirus, non-SARS-CoV-2 coronaviruses, adenovirus, enterovirus/rhinovirus) involves the use of data from clinical sentinel laboratories (hospital, academic or private) located throughout California. Specimens for testing are collected from patients in healthcare settings and do not reflect all testing for influenza, respiratory syncytial virus, and other respiratory viruses in California. These laboratories report the number of laboratory-confirmed influenza, respiratory syncytial virus, and other respiratory virus detections and isolations, and the total number of specimens tested by virus type on a weekly basis. Test positivity for a given week is calculated by dividing the number of positive COVID-19, influenza, RSV, or other respiratory virus results by the total number of specimens tested for that virus. Weekly laboratory surveillance data are defined as Sunday through Saturday. Hospitalization data: Data on COVID-19 and influenza hospital admissions will be included after the National Healthcare Safety Network (NHSN) Hospitalization Data reporting requirement goes into effect on November 1, 2024. Data will not be available immediately after November 1, 2024, to account for data preparation and quality checks. CDPH collaborates with Northern California Kaiser Permanente (NCKP) to monitor trends in RSV admissions. The percentage of RSV admissions is calculated by dividing the number of RSV-related admissions by the total number of admissions during the same period. Admissions for pregnancy, labor and delivery, birth, and outpatient procedures are not included in total number of admissions. These admissions serve as a proxy for RSV activity and do not necessarily represent laboratory confirmed hospitalizations for RSV infections; NCKP members are not representative of all Californians. Weekly hospitalization data are defined as Sunday through Saturday. Death certificate data: CDPH receives weekly year-to-date dynamic data on deaths occurring in California from the CDPH Center for Health Statistics and Informatics. These data are limited to deaths occurring among California residents and are analyzed to identify influenza, respiratory syncytial virus, and COVID-19-coded deaths. These deaths are not necessarily laboratory-confirmed and are an underestimate of all influenza, respiratory syncytial virus, and COVID-19-associated deaths in California. Weekly death data are defined as Sunday through Saturday. Wastewater data: This dataset represents statewide weekly SARS-CoV-2 wastewater summary values. SARS-CoV-2 wastewater concentrations from all sites in California are combined into a single, statewide, unit-less summary value for each week, using a method for data transformation and aggregation developed by the CDC National Wastewater Surveillance System (NWSS). Please see the CDC NWSS data methods page for a description of how these summary values are calculated. Weekly wastewater data are defined as Sunday through Saturday.

Data is from the California Department of Public Health (CDPH) Respiratory Virus Weekly Report.

The report is updated each Friday.

Laboratory surveillance data: California laboratories report SARS-CoV-2 test results to CDPH through electronic laboratory reporting. Los Angeles County SARS-CoV-2 lab data has a 7-day reporting lag. Test positivity is calculated using SARS-CoV-2 lab tests that has a specimen collection date reported during a given week.

Laboratory surveillance for influenza, respiratory syncytial virus (RSV), and other respiratory viruses (parainfluenza types 1-4, human metapneumovirus, non-SARS-CoV-2 coronaviruses, adenovirus, enterovirus/rhinovirus) involves the use of data from clinical sentinel laboratories (hospital, academic or private) located throughout California. Specimens for testing are collected from patients in healthcare settings and do not reflect all testing for influenza, respiratory syncytial virus, and other respiratory viruses in California. These laboratories report the number of laboratory-confirmed influenza, respiratory syncytial virus, and other respiratory virus detections and isolations, and the total number of specimens tested by virus type on a weekly basis.

Test positivity for a given week is calculated by dividing the number of positive COVID-19, influenza, RSV, or other respiratory virus results by the total number of specimens tested for that virus. Weekly laboratory surveillance data are defined as Sunday through Saturday.

Hospitalization data: Data on COVID-19 and influenza hospital admissions are from Centers for Disease Control and Prevention’s (CDC) National Healthcare Safety Network (NHSN) Hospitalization dataset. The requirement to report COVID-19 and influenza-associated hospitalizations was effective November 1, 2024. CDPH pulls NHSN data from the CDC on the Wednesday prior to the publication of the report. Results may differ depending on which day data are pulled. Admission rates are calculated using population estimates from the P-3: Complete State and County Projections Dataset provided by the State of California Department of Finance (https://dof.ca.gov/forecasting/demographics/projections/). Reported weekly admission rates for the entire season use the population estimates for the year the season started. For more information on NHSN data including the protocol and data collection information, see the CDC NHSN webpage (https://www.cdc.gov/nhsn/index.html).

CDPH collaborates with Northern California Kaiser Permanente (NCKP) to monitor trends in RSV admissions. The percentage of RSV admissions is calculated by dividing the number of RSV-related admissions by the total number of admissions during the same period. Admissions for pregnancy, labor and delivery, birth, and outpatient procedures are not included in total number of admissions. These admissions serve as a proxy for RSV activity and do not necessarily represent laboratory confirmed hospitalizations for RSV infections; NCKP members are not representative of all Californians.

Weekly hospitalization data are defined as Sunday through Saturday.

Death certificate data: CDPH receives weekly year-to-date dynamic data on deaths occurring in California from the CDPH Center for Health Statistics and Informatics. These data are limited to deaths occurring among California residents and are analyzed to identify influenza, respiratory syncytial virus, and COVID-19-coded deaths. These deaths are not necessarily laboratory-confirmed and are an underestimate of all influenza, respiratory syncytial virus, and COVID-19-associated deaths in California. Weekly death data are defined as Sunday through Saturday.

Wastewater data: This dataset represents statewide weekly SARS-CoV-2 wastewater summary values. SARS-CoV-2 wastewater concentrations from all sites in California are combined into a single, statewide, unit-less summary value for each week, using a method for data transformation and aggregation developed by the CDC National Wastewater Surveillance System (NWSS). Please see the CDC NWSS data methods page for a description of how these summary values are calculated. Weekly wastewater data are defined as Sunday through Saturday.

People infected with COVID-19 can shed the virus through their stool, even if they don't have any symptoms. Testing a community's sewage (wastewater) can tell us if COVID-19 is increasing or decreasing in that community. Our scientists have developed a pan-Canadian wastewater network to monitor the spread of COVID-19 in Canada. This is in collaboration with provincial, territorial and municipal governments and academia across Canada. Some communities and local health authorities are collecting wastewater samples for analysis by Canada's National Microbiology Laboratory. Analysis helps detect the virus that causes COVID-19 and variants.

This dataset was produced through the joint collection of Statistics Canada's Canadian Wastewater Survey (CWS) with the Public Health Agency of Canada. The CWS measures levels of SARS-CoV-2 in the wastewater of five Canadian municipalities: Vancouver, Edmonton, Toronto, Montreal, and Halifax. The dataset includes measurements by RT-qPCR of the concentration of SARS-CoV-2 and Pepper Mild Mottle Virus (PMMV) in wastewater from 2021/04/01 to 2021/12/15 reported in the Public Health Environmental Surveillance Open Data Model v1.1.

People infected with COVID-19 can shed the virus through their stool, even if they don't have any symptoms. Testing a community's sewage (wastewater) can tell us if COVID-19 is increasing or decreasing in that community. Our scientists have developed a pan-Canadian wastewater network to monitor the spread of COVID-19 in Canada. This is in collaboration with provincial, territorial and municipal governments and academia across Canada. Some communities and local health authorities are collecting wastewater samples for analysis by Canada's National Microbiology Laboratory. Analysis helps detect the virus that causes COVID-19 and variants.

Wastewater SARS-CoV-2 and PMMoV data were collected between December 2021 and June 2022 from 13 sewer manholes on University of California Irvine campus. These manholes serve 7 student communities with population sizes between 300 and 4000 people. The samples were analyzed using RT-ddPCR. The dataset shows SARS-CoV-2 N2 and E gene concentrations as well as Pepper Mild Mottle Virus (PMMoV) concentrations in 726 wastewater samples.

SARS-CoV-2 wastewater surveillance data and metadata in the Open Data Model format. Part 1: Québec City Authors

• Therrien, J-D¹
• Maere, T.¹
• Sanchez-Quete, F.²
• Tsitouras, A.²
• Goitom, E.³
• Cloutier, F.⁴
• Dufour, D.⁴
• Proulx, F. ⁴
• Nicolaï, N.¹
• Philippe, R.¹
• Tohidi, M.¹
• Dorner, S.³
• Frigon, D.²
• Vanrolleghem, P.A.¹

Affiliations

• ¹ modelEAU, Département de génie civil et de génie des eaux, Université Laval
• ² Microbial Community Engineering Lab (MiCEL), Department of Civil Engineering, McGill University
• ³ Polytechnique Montréal
• ⁴ Ville de Québec

General Remarks

Wastewater-based surveillance of SARS-CoV-2 virus can detect between 1 and 30 infected individuals per 100,000 (including asymptomatic ones) by analyzing the population's sewage. As such, this method is very attractive since it costs only a fraction of clinical testing (as low as 1%). Human faeces may contain the virus a few days before a person becomes ill. Thus, this approach allows for detection of outbreaks 2-7 days before the increase in reported cases stemming from clinical screening tests (Bibby et al., 2021). Wastewater-based surveillance complements clinical testing by geolocating outbreaks, which may help targeting intensive screening programs. Moreover, it provides a quick indication of whether new public health measures (e.g., masks, social distancing, confinement, and curfew) are effective.

Sampling

The reported dataset contains open data collected in the province of Québec as part of the SARS-CoV-2 wastewater-based surveillance program CentrEau-COVID. Four of the largest cities in the province (Montréal, Laval, Québec City, and Trois-Rivières), as well as the municipalities of four rural regions (Mauricie, Centre-du-Québec, Bas-St-Laurent, and Gaspésie) participated in the program. The entire dataset includes 31 sampling sites covering approximately half the population of the province of Québec (population size of 8.5 million). The timeframe covered by the dataset varies for each site. The earliest surveillance program was launched in March 2020, others followed soon after. Samples were collected using various methods, such as 24h composite samples, grab samples, and passive sampling using variations on the Moore swab method (Schang et al., 2020)

Analysis

Prior to the analysis of the samples for SARS-CoV-2, physiochemical parameters such as total suspended solids (TSS), turbidity, conductivity, ammonium concentration, and pH were measured. The samples were subsequently concentred by filtration using a MEC filter (0.45 um), followed by total RNA extraction using the Qiagen AllPrep PowerViral DNA/RNA Kit (Qiagen, USA) with some modifications (beta-mercaptoethanol concentration raised to 10% and lysis performed at 55 °C for 30 minutes) (Ahmed et al., 2020). SARS-CoV-2 viral RNA was detected by a one-step RT-qPCR. To assess the RNA recovery rate of the procedure, samples were spiked before extraction with a known concentration of Bovine Respiratory Syncytial Virus (BRSV) using the Zoetis INFORCE 3 vaccine (Zoetis, USA). In addition to SARS-CoV-2, samples were assessed for Pepper Mild Mottle Virus (PMMoV), the daily load of which is hypothesized to represent the fecal load contributions to the samples at a given site and time. PCR conditions and primer used to collect viral data are described in the files primers.md and PCR conditions.md.

Compilation

The measurements on wastewater samples carried out by the participating laboratories of this study are found in the WWMeasure table. The values provided by municipalities come from laboratories accredited by the Centre d'expertise en analyse environnementale du Québec (CEAEQ), in compliance with the latter's quality assurance protocols. The COVID-19-related public health data found in the CPHD table were collected from the Institut National de Santé Publique du Québec (INSPQ)'s public reports. Wastewater data taken in-situ at the sampling sites (e.g., the flow at pumping stations or water resource recovery facilities (WRRFs)) are found in the SiteMeasure table and were taken by the institutions responsible for managing the sites. All of the data, stemming from multiple sources, were combined into the Open Data Model (ODM) standard format using the ODM-Import python package (see also Structure).

Validation

Wastewater and sample data were manually assessed for quality by our research collaborators. Data points for which the quality appeared to be uncertain were tagged with the value True in the qualityFlag column. Conversely, data deemed of good quality have a quality flag of False. Data that were not checked have a quality flag of NA. Textual comments describing the issues with the data points in more detail are also included in the dataset using the notes column of the relevant tables. Note that data validation was carried out by the data custodians responsible for each city in the dataset according to available resources. As the project continues and data validation is undertaken on more sections of the dataset, data may be re-analyzed, flagged, or commented as needed. Revisions to the dataset will be reported to the best of our ability.

Structure

The data contained in this dataset has been structured according to the Open Data Model (ODM) for Wastewater-Based Surveillance. This model provides a standardized dictionary to collect and share data and metadata stemming from wastewater-based surveillance programs. By convention, it splits all data into 10+ thematic tables with each record representing a unique measurement, i.e., long format. For convenience, the wide folder presents the data found in all the other tables in a wide format, i.e., multiple measurements are aligned by timestamp, with each column representing a different parameter.

Acknowledgements

The authors would like to acknowledge that this dataset was collected thanks to the financial support of the Fonds de Recherche du Québec, the Molson Foundation, the Trottier Family Foundation, CentrEau and NSERC. The authors would also like to acknowledge the efforts of Douglas Manuel (Ottawa Hospital) and Howard Swerdfeger (Public Health Agency of Canada) for their original idea for the Open Data Model and continued development.

References

1. Ahmed, W., Bertsch, P.M., Bivins, A., Bibby, K., Farkas, K., Gathercole, A., Haramoto, E., Gyawali, P., Korajkic, A., McMinn, B.R., Mueller, J.F., Simpson, S.L., Smith, W.J.M., Symonds, E.M., Thomas, K. v., Verhagen, R., Kitajima, M., 2020. Comparison of virus concentration methods for the RT-qPCR-based recovery of murine hepatitis virus, a surrogate for SARS-CoV-2 from untreated wastewater. Science of the Total Environment 739. https://doi.org/10.1016/j.scitotenv.2020.139960

2. Bibby, K., Bivins, A., Wu, Z., North, D., 2021. Making waves: Plausible lead time for wastewater based epidemiology as an early warning system for COVID-19. Water Research 202, 117438. https://doi.org/10.1016/j.watres.2021.117438

3. Schang, C., Crosbie, N., Nolan, M., Poon, R., Wang, M., Jex, A., Scales, P., Schmidt, J., Thorley, B.R., Henry, R., Kolotelo, P., Langeveld, J., Schilperoort, R., Shi, B., Einsiedel, S., Thomas, M., Black, J., Wilson, S., McCarthy, D.T., 2020. Passive sampling of viruses for wastewater-based epidemiology: a case-study of SARS-CoV-2 [WWW Document]. URL https://www.researchgate.net/publication/347103410\_Passive\_sampling\_of\_viruses\_for\_wastewater-based\_epidemiology\_a\_case-study\_of\_SARS-CoV-2?channel=doi&linkId=5fd800f392851c13fe892393&showFulltext=true (accessed 1.18.21).

The California Department of Public Health (CDPH) aggregates confirmed cases of COVID-19 by sewershed restricted locations. Confirmed cases are defined as individuals with a positive molecular test, which tests for viral genetic material, such as a polymerase chain reaction test. Since wastewater data available starts from January 1st, 2021, rather than the beginning of the COVID-19 pandemic in 2020, the cumulative counts of the confirmed cases variable are shown as “NA”. Please note that values less than 5 for confirmed cases are masked (shown as “Masked”) if the sewershed population size is 50,000 or fewer, in accordance with de-identification guidelines. Values less than 3 for cases are masked (shown as “Masked”) if the sewershed population size is between 50,001 and 250,000. For no confirmed cases reported, values are set as zero.