The National Wastewater Surveillance System (NWSS): From inception to widespread coverage, 2020-2022, United States

Abstract

Wastewater surveillance is a valuable tool that can be used to track infectious diseases in a community. In September 2020, the Centers for Disease Control and Prevention (CDC) established the National Wastewater Surveillance System (NWSS) to coordinate and build the nation's capacity to detect and quantify concentrations of SARS-CoV-2 RNA in U.S. wastewater. This is the first surveillance summary of NWSS, covering September 1, 2020 to December 31, 2022. Through partnerships with state, tribal, local, and territorial health departments, NWSS became a national surveillance platform that can be readily expanded and adapted to meet changing public health needs. Beginning with 209 sampling sites in September 2020, NWSS rapidly expanded to >1500 sites by December 2022, covering ≈47 % of the U.S. population. As of December 2022, >152,000 unique wastewater samples have been collected by NWSS partners, primarily from wastewater treatment plants (WWTPs). WWTPs participating in NWSS tend to be larger than the average U.S. WWTP and serve more populated communities. In December 2022, ≈8 % of the nearly 16,000 U.S. WWTPs were participating in NWSS. NWSS partners used a variety of methods for sampling and testing wastewater samples; however, progress is being made to standardize these methods. In July 2021, NWSS partners started submitting SARS-CoV-2 genome sequencing data to NWSS. In October 2022, NWSS expanded to monkeypox virus testing, with plans to include additional infectious disease targets in the future. Through the rapid implementation and expansion of NWSS, important lessons have been learned. Wastewater surveillance programs should consider both surge and long-term capacities when developing an implementation plan, and early standardization of sampling and testing methods is important to facilitate data comparisons across sites. NWSS has proven to be a flexible and sustainable surveillance system that will continue to be a useful complement to case-based surveillance for guiding public health action.

Keywords: COVID-19; Infectious diseases; Mpox; Public health; SARS-CoV-2; Wastewater surveillance.

Fig. 1.

Number of wastewater surveillance sampling sites participating in the CDC’s National Wastewater Surveillance System (NWSS) by week^a,b: September 1, 2020 – December 31, 2022^c. Abbreviations: CDC, Centers for Disease Control and Prevention. ^a Sites that collected ≥1 sample in a week (Sunday-Saturday) were included in that week’s counts. ^b The decline in health department sites collecting samples at the end of December 2022 was most likely due to reduced sampling over the holiday period. The number of health department sites sampling in January 2023 returned to pre-holiday levels (not shown). ^c Data were downloaded August 31, 2023 and restricted to samples collected prior to January 1, 2023.

Fig. 2.

Locations of wastewater surveillance sites^a,b participating in the CDC’s National Wastewater Surveillance System (NWSS): September 1, 2020 – December 31, 2022. Abbreviations: CDC, Centers for Disease Control and Prevention. ^a Each point on the map represents a wastewater surveillance site. A site can represent all or part of a sewershed, which is the geographic area contributing wastewater to a sampling location. Sewersheds may cross county or state boundaries. ^b Sites are plotted at the centroid of the ZIP code in which they are located and then jittered, so points on the map do not correspond to exact sampling locations. ^c Year added was determined by the first sample collection date for a site.

Fig. 3.

Counties in the United States and U.S. territories^a by Rural-Urban Continuum Codes (RUCC)^b; counties covered by CDC’s National Wastewater Surveillance System (NWSS)^c are shown by brighter colors: September 1, 2020 – December 31, 2022. Abbreviations: CDC, Centers for Disease Control and Prevention; RUCC, Rural-Urban Continuum Codes. ^a U.S. territories include Guam and Puerto Rico. ^b Data are from the U.S. Department of Agriculture (USDA) 2013 Urban-Rural Continuum Codes dataset: https://www.ers.usda.gov/data-products/rural-urban-continuum-codes/. RUCC is a classification from 0 to 9, with higher values indicating more rural counties. ^c Counties are considered to be covered by NWSS if they were served entirely or partially by one or more NWSS sampling site (i.e., at least 1 site serving the county collected at least 1 sample between September 1, 2020 and December 31, 2022). A site can serve all or part of a sewershed, which is the geographic area contributing wastewater to a sampling location. Sewersheds may cross county or state boundaries.

Fig. 4.

Counties in the United States and U.S. territories^a by Social Vulnerability Index (SVI)^b; counties covered by CDC’s National Wastewater Surveillance System (NWSS)^c are shown by brighter colors: September 1, 2020 – December 31, 2022^d. Abbreviations: CDC, Centers for Disease Control and Prevention; SVI, Social Vulnerability Index. ^a U.S. territories include Guam and Puerto Rico. ^b Data are from the CDC/Agency for Toxic Substances and Disease Registry (ATSDR) 2020 Social Vulnerability Index dataset: https://www.atsdr.cdc.gov/placeandhealth/svi/index.html. SVI is a measure from 0 to 1, with higher values indicating greater vulnerability in a public health emergency. ^c Counties are considered to be covered by NWSS if they were served entirely or partially by one or more NWSS sampling site (i.e., at least 1 site serving the county collected at least 1 sample between September 1, 2020 and December 31, 2022). A site can serve all or part of a sewershed, which is the geographic area contributing wastewater to a sampling location. Sewersheds may cross county or state boundaries. ^d Counties with missing SVI data are shown in gray.