Since the early days of public health, wastewater has been an important tool for monitoring the spread of infection. For a series of diseases, particles are excreted through waste in some form or another allowing us to evaluate the presence and risk of these viruses. Dr. John Snow first utilized this practice in the 19th Century to track the Broad Street cholera outbreak in London. He convinced city officials to commit to this process despite the concept of germ theory having yet to be proven–which is the idea that specific microscopic organisms cause diseases to spread (Casanova and Abel, 2013). His work successfully identified where the outbreak was occurring; since then, wastewater has been an important resource for public health. Similar work was done to track polio outbreaks in the 20th century, but it was not until the early 2000s that breakthroughs in large-scale tracking occurred (Gao et al., 2023). Individual communities had wastewater surveillance systems to track for specific viruses over the past few decades, giving health departments the ability to identify regions of their communities spreading disease.

The wastewater technology itself has remained much the same over the past 20 years with treatment plants covering nearly the entire country. Today, all large cities in the U.S. have wide-scale treatment plants that all waste filters through with smaller communities having septic systems. Treatment plants are used to first extract solids that should not end up in open water, such as paper; then the organic solid matter is separated in large filtration tanks to create a substance called “sludge.” Two more treatments occur afterward, which aim to destroy harmful bacteria and further clean the wastewater before it is released to open bodies of water (CDC, 2023). Scientists can then determine if viral particles are released in waste and public health officials, in turn, can sample various plants to locate areas with the potential for higher spread.

Before the COVID-19 pandemic, there was no wide- scale tracking system in the U.S., but rather individual communities focused on specific diseases. Once it was discovered that viral particles traveled in sewage and could survive for around two days, the Centers for Disease Control and Prevention (CDC) developed a national database to collect information from treatment plants across the nation–the National Wastewater Surveillance System (NWSS) (Sherchan et al., 2023). They measured the amount of SARS- CoV-2 RNA particles present in sample collections and were able to create risk levels based on how much disease was present in the community by comparing various metrics such as positivity rate, hospitalizations, etc. One of the biggest strengths of this practice is that the virus could be identified despite individuals who were asymptomatic or not getting tested–the wastewater depicted an unfiltered insight into where COVID-19 was present (Bivins et al., 2020). This also meant that areas without sufficient access to in-person testing methods could be monitored for the virus, increasing accessibility and coverage (Murakami et al., 2020). The data collected by health departments and the CDC was pooled, so individual households could not be identified but rather sections of the community. Officials utilized this information when making decisions on how to alter interventions to reduce spread. The numbers relied on how extensively the local health departments sampled wastewater, hence the use of data varied greatly among different cities. It is also important to note that this new program was a collaboration between the CDC, state, local, and tribal health departments–an example of a truly multi-stakeholder partnership (Adams et al., 2024). Although the technology itself has been present for quite some time, the NWSS is a novel system that transformed how wastewater tracking is utilized and demonstrates massive potential in the case of future pandemics or disease outbreaks.

Wastewater tracking of SARS-CoV-2 through the NWSS helped highlight trends and outbreaks regardless of testing or symptomatic trends, which was an effective additional tool that guided public health decision- making. Concerns regarding privacy and accessibility exist, but the NWSS should be expanded for other pathogens and more communities in the U.S. Next month’s edition will explore how the City of Houston utilized this technology for effective interventions and, in turn, how it impacted health outcomes.

References:

Adams C, Bias M, Welsh RM, et al. The National Wastewater Surveillance System (NWSS): From inception to widespread coverage, 2020–2022, United States. Science of The Total Environment 2024; 924:171566.

Bivins A, North D, Ahmad A, et al. Wastewater- Based Epidemiology: Global Collaborative to Maximize Contributions in the Fight Against COVID-19. Environmental Science & Technology 2020; 54:7754–7757.

Casanov J-L & Abel L. The Genetic Theory of Infectious Diseases: A Brief History and Selected Illustrations. Annual Review of Genomics and Human Genetics 2013; 14: 215.

CDC. How Wastewater Monitoring Works. Centers for Disease Control and Prevention.2023. https://www.cdc. gov/nwss/how-wws-works.html

Gao Z, Gao M, Chen C, et al. Knowledge graph of wastewater-based epidemiology development: A data-driven analysis based on research topics and trends. Environmental Science and Pollution Research International 2023; 30:28373–28382.

Murakami M, Hata A, Honda R, & Watanabe T. Letter to the Editor: Wastewater-Based Epidemiology Can Overcome Representativeness and Stigma Issues Related to COVID-19. Environmental Science & Technology 2020; 54:5311.

Sherchan S, Thakali O, Ikner LA, & Gerba CP (2023). Survival of SARS-CoV-2 in wastewater. The Science of the Total Environmen 2023; 882: 163049.