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. 2023 Jun 27:11:e15631.
doi: 10.7717/peerj.15631. eCollection 2023.

Divergence of wastewater SARS-CoV-2 and reported laboratory-confirmed COVID-19 incident case data coincident with wide-spread availability of at-home COVID-19 antigen tests

Alexandria B Boehm  1 , Marlene K Wolfe  2 , Bradley White  3 , Bridgette Hughes  3 , Dorothea Duong  3
Affiliations

Divergence of wastewater SARS-CoV-2 and reported laboratory-confirmed COVID-19 incident case data coincident with wide-spread availability of at-home COVID-19 antigen tests

Alexandria B Boehm et al. PeerJ. .

Abstract

Concentrations of SARS-CoV-2 RNA in wastewater settled solids from publicly owned treatment works (POTWs) historically correlated strongly with laboratory confirmed incident COVID-19 case data. With the increased availability of at-home antigen tests since late 2021 and early 2022, laboratory test availability and test seeking behavior has decreased. In the United States, the results from at-home antigen tests are not typically reportable to public health agencies and thus are not counted in case reports. As a result, the number of reported laboratory-confirmed incident COVID-19 cases has decreased dramatically, even during times of increased test positivity rates and wastewater concentrations of SARS-CoV-2 RNA. Herein, we tested whether the correlative relationship between wastewater concentrations of SARS-CoV-2 RNA and reported laboratory-confirmed COVID-19 incidence rate has changed since 1 May 2022, a point in time immediately before the onset of the BA.2/BA.5 surge, the first surge to begin after at-home antigen test availability was high in the region. We used daily data from three POTWs in the Greater San Francisco Bay Area of California, USA for the analysis. We found that although there is a significant positive association between wastewater measurements and incident rate data collected after 1 May 2022, the parameters describing the relationship are different than those describing the relationship between the data collected prior to 1 May 2022. If laboratory test seeking or availability continues to change, the relationship between wastewater and reported case data will continue to change. Our results suggest, assuming SARS-CoV-2 RNA shedding remains relatively stable among those infected with the virus as different variants emerge, that wastewater concentrations of SARS-CoV-2 RNA can be used to estimate COVID-19 cases as they would have been during the time when laboratory testing availability and test seeking behavior were at a high (here, before 1 May 2022) using the historical relationship between SARS-CoV-2 RNA and COVID-19 case data.

Keywords: COVID-19; COVID-19 antigen tests; Public health; SARS-CoV-2; Viruses; Wastewater-based epidemiology.

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Conflict of interest statement

Bradley J. White, Dorothea Duong, and Bridgette Hughes are employees of Verily Life Sciences, LLC. There are no other competing interests.

Figures

Figure 1
Figure 1. Data for Sacramento POTW.
Top panel: Sacramento (SAC) time series of concentrations of N and N/PMMoV in wastewater, incidence rates (IRs), and positivity rates (PRs) between 1 December 2020 until 16 January 2023. IRs and PRs are unitless. The solid lines represent 5-d trimmed averages for the wastewater data, and 7-d moving averages for the incidence and positivity rates. The county-aggregated and sewershed-aggregated incidence rate data fall almost directly on top of each other, obscuring the view of both. The scales for incidence and positivity rates are on the left and right axes, respectively. Middle and bottom panels: County-aggregated (Sacramento County, SAC) positivity rate and incidence rate versus 5-d trimmed N/PMMoV; white symbols are data collected on and after 1 May 2022.
Figure 2
Figure 2. Data for Oceanside POTW.
Top panel: Oceanside (OS) time series of concentrations of N and N/PMMoV in wastewater, incidence rates (IRs), and positivity rates (PRs) between 1 December 2020 until 16 January 2023. IRs and PRs are unitless. The solid lines represent 5-d trimmed averages for the wastewater data, and 7-d moving averages for the incidence and positivity rates. The county-aggregated and sewershed-aggregated incidence rate data fall almost directly on top of each other, obscuring the view of both. The scales for incidence and positivity rates are on the left and right axes, respectively. Middle and bottom panels: County-aggregated (San Francisco County, SF) positivity rate and incidence rate versus 5-d trimmed N/PMMoV; white symbols are data collected on and after 1 May 2022.
Figure 3
Figure 3. Data for San Jose POTW.
Top panel: San Jose (SJ) time series of concentrations of N and N/PMMoV in wastewater, incidence rates (IRs), and positivity rates (PRs) between 1 December 2020 until 16 January 2023. IRs and PRs are unitless. The solid lines represent 5-d trimmed averages for the wastewater data, and 7-d moving averages for the incidence and positivity rates. The county-aggregated and sewershed-aggregated incidence rate data fall almost directly on top of each other, obscuring the view of both. The scales for incidence and positivity rates are on the left and right axes, respectively. Middle and bottom panels: County-aggregated (Santa Clara County, SC) Positivity rate and incidence rate versus 5-d trimmed N/PMMoV; white symbols are data collected on and after 1 May 2022.
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