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Observational Study
. 2023 Jul 3;6(7):e2325591.
doi: 10.1001/jamanetworkopen.2023.25591.

Use of Wastewater Metrics to Track COVID-19 in the US

Meri R J Varkila  1 , Maria E Montez-Rath  2 , Joshua A Salomon  3 , Xue Yu  2 , Geoffrey A Block  4 , Douglas K Owens  3 , Glenn M Chertow  2   5 , Julie Parsonnet  1   5 , Shuchi Anand  2
Affiliations
Observational Study

Use of Wastewater Metrics to Track COVID-19 in the US

Meri R J Varkila et al. JAMA Netw Open. .

Abstract

Importance: Widespread use of at-home COVID-19 tests hampers determination of community COVID-19 incidence.

Objective: To examine the association of county-level wastewater metrics with high case and hospitalization rates nationwide both before and after widespread use of at-home tests.

Design, setting, and participants: This observational cohort study with a time series analysis was conducted from January to September 2022 in 268 US counties in 22 states participating in the US Centers for Disease Control and Prevention's National Wastewater Surveillance System. Participants included the populations of those US counties.

Exposures: County level of circulating SARS-CoV-2 as determined by metrics based on viral wastewater concentration relative to the county maximum (ie, wastewater percentile) and 15-day percentage change in SARS-CoV-2 (ie, percentage change).

Main outcomes and measures: High county incidence of COVID-19 as evidenced by dichotomized reported cases (current cases ≥200 per 100 000 population) and hospitalization (≥10 per 100 000 population lagged by 2 weeks) rates, stratified by calendar quarter.

Results: In the first quarter of 2022, use of the wastewater percentile detected high reported case (area under the curve [AUC], 0.95; 95% CI, 0.94-0.96) and hospitalization (AUC, 0.86; 95% CI, 0.84-0.88) rates. The percentage change metric performed poorly, with AUCs ranging from 0.51 (95% CI, 0.50-0.53) to 0.57 (95% CI, 0.55-0.59) for reported new cases, and from 0.50 (95% CI, 0.48-0.52) to 0.55 (95% CI, 0.53-0.57) for hospitalizations across the first 3 quarters of 2022. The Youden index for detecting high case rates was wastewater percentile of 51% (sensitivity, 0.82; 95% CI, 0.80-0.84; specificity, 0.93; 95% CI, 0.92-0.95). A model inclusive of both metrics performed no better than using wastewater percentile alone. The performance of wastewater percentile declined over time for cases in the second quarter (AUC, 0.84; 95% CI, 0.82-0.86) and third quarter (AUC, 0.72; 95% CI, 0.70-0.75) of 2022.

Conclusions and relevance: In this study, nationwide, county wastewater levels relative to the county maximum were associated with high COVID-19 case and hospitalization rates in the first quarter of 2022, but there was increasing dissociation between wastewater and clinical metrics in subsequent quarters, which may reflect increasing underreporting of cases, reduced testing, and possibly lower virulence of infection due to vaccines and treatments. This study offers a strategy to operationalize county wastewater percentile to improve the accurate assessment of community SARS-CoV-2 infection prevalence when reliability of conventional surveillance data is declining.

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Conflict of interest statement

Conflict of Interest Disclosures: Dr Varkila reported receiving nonfinancial support from Ascend Clinical Laboratory and Abbott Laboratory (COVID-19 testing materials) during the conduct of the study. Dr Salomon reported receiving grants from Centers for Disease Control and Prevention to their institution through the Council of State and Territorial Epidemiologists during the conduct of the study. Dr Block reported being the Associate Chief Medical Officer at US Renal Care, Inc. Dr Chertow reported receiving personal fees from Akebia, Ardelyx, ReCor, Mineralys, Bayer, Vertex, Sanifit, Gilead, Reata, Satellite Healthcare, and AstraZeneca; stock options from CloudCath, Unicycive, Renibus, Outset, Miromatrix, and Durect; and grants from CSL Behring outside the submitted work. Dr Parsonnet reported receiving grants from Heluna Health, Max Planck Institute, and Gauss, Inc, outside the submitted work. Dr Anand reported receiving nonfinancial support from Abbott (study material kit) and Ascend Clinical (samples processing) and personal fees from Vera Therapeutics and HealthPals, Inc, consulting outside the submitted work No other disclosures were reported.

Figures

Figure 1.
Figure 1.. US Counties Submitting Wastewater Surveillance Data to the National Wastewater Surveillance System (NWSS) Between January 1, 2022, and September 30, 2022
Regions mapped in dark blue show counties included in the analysis (n = 268). Regions mapped in light blue show counties that submitted the wastewater data to NWSS, but were excluded from analysis (n = 462).
Figure 2.
Figure 2.. Time History of Wastewater Surveillance Data and Clinical Case Metrics From Los Angeles County, California, January 2022 and September 2022
A, Graph shows smoothed spline-fit polymerase chain reaction (PCR) concentrations of SARS-CoV-2 for each sampling location as reported by the Centers for Disease Control and Prevention National Wastewater Surveillance System. B, Graph shows reported COVID-19 cases per 100 000 population. C, Graph shows wastewater SARS-CoV-2 percentile level. D, Graph shows COVID-19 hospital admissions per 100 000 population. Horizontal dashed lines in B and D show thresholds for high COVID-19 community level (reported COVID-19 case rate ≥200 per 100 000 population and reported hospitalization rate ≥10 new inpatient admissions per 100 000 population, respectively). E, Graph shows wastewater SARS-CoV-2 15-day percentage change. F, Graph shows state-level data for diagnostic laboratory tests per 100 000 population (solid black line shows reported tests from the state of California; dashed gray blue show estimates for all other US states; dashed vertical orange line represents the date when distribution of rapid home tests was announced by the Biden administration, January 19, 2022). The solid blue lines in panels A, B, C, D, and F show weighted mean values using each sewershed’s population served. Data for the most populous counties in US Census regions Midwest and Northeast are shown in eFigure 4 in Supplement 1.
Figure 3.
Figure 3.. Time History of Wastewater Surveillance Data and Clinical Case Metrics From Harris County, Texas, January 2022 and September 2022
A, Graph shows smoothed spline-fit polymerase chain reaction (PCR) concentrations of SARS-CoV-2 for each sampling location as reported by the Centers for Disease Control and Prevention National Wastewater Surveillance System. When multiple sewersheds were sampled within a county, dashed gray lines in panel A represent individual sewersheds. B, Graph shows reported COVID-19 cases per 100 000 population. C, Graph shows wastewater SARS-CoV-2 percentile level. D, Graph shows COVID-19 hospital admissions per 100 000 population. Horizontal dashed lines in B and D show thresholds for high COVID-19 community level (reported COVID-19 case rate ≥200 per 100 000 population and reported hospitalization rate ≥10 new inpatient admissions per 100 000 population, respectively). E, Graph shows wastewater SARS-CoV-2 15-day percentage change. F, Graph shows state-level data for diagnostic laboratory tests per 100 000 population (solid blue lines show reported tests from the state of Texas; dashed gray lines show estimates for all other US states; dashed vertical orange line represents the date when distribution of rapid home tests was announced by the Biden administration, January 19, 2022). The solid blue lines in panels A, B, C, D, and F show weighted mean values using each sewershed’s population served. Data for the most populous counties in US Census regions Midwest and Northeast are shown in eFigure 4 in Supplement 1.
Figure 4.
Figure 4.. Performance of Wastewater Percentile in Reference to Clinical Case Metrics Stratified by Calendar Quartile of 2022
Graphs show areas under the curve (AUCs) of wastewater percentile in reference to current reported COVID-19 cases (≥200 per 100 000 population) (A) and new hospital admissions in 2 weeks (≥10 per 100 000 population) (B). Shaded ribbons show bootstrapped 95% CIs for sensitivity at given specificity.
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