Tracking SARS-CoV-2 and Its Variants in Wastewater: An Old Technique Is Yielding Powerful New Insights in the Covid-19 Pandemic

Data about the presence of SARS-CoV-2 RNA in wastewater can be used to monitor trends in community transmission and to inform public health decisions. Wastewater surveillance can provide early indications of community transmission or surges in Covid-19, sometimes preceding reports of positive clinical samples by 1-2 weeks, giving health systems critical lead time. Declines in wastewater virus levels may also precede drops in clinical cases.

In the early months of the pandemic, hundreds of studies demonstrated the feasibility of using wastewater surveillance to track SARS-CoV-2. On a national level, several countries, including Australia, India, Israel, the Netherlands, Pakistan, and Sweden, were able to pivot existing wastewater surveillance programs to Covid-19. Currently, at least 58 countries monitor wastewater at some level. Many of the more than 16,000 water treatment plants within the US are monitoring wastewater, and the CDC tracker is a first step toward a coordinated national system in the US. As more sites come online, and as methods are standardized, the value of the tracker will continue to increase after this promising first step.

Wastewater sampling at a centralized water treatment facility can provide information for a city or region within its sewershed, the area from which wastewater arrives at a single treatment plant. Sampling at smaller sewer catchment areas within the larger sewersheds, such as via manholes, can provide more focused information, sometimes down to the neighborhood level. Any “hot spots” that are detected can then be identified for targeted public health intervention and mitigation.

One such “hot spot” was detected in Louisville, Kentucky during the onset of their 2021 Omicron variant surge. The Pandemic Prevention Institute (PPI) partners at the University of Louisville track SARS-CoV-2 in small wastewater catchment areas, which complements the clinical data collected by the Louisville Metro Department of Public Health & Wellness. Prior to Omicron, clinical cases reported within the 40212 ZIP code had been roughly comparable to those of the city, but beginning in November 2021, wastewater data painted a different picture. With wastewater, Louisville was able to zoom in more closely into the community and noted that only part of the 40212 ZIP code was showing unusual patterns of virus prevalence. Specifically, in contrast to the clinical case data, wastewater data showed much higher levels of virus in the Shawnee Park area of 40212, compared to the 34th Street area and to the larger sewershed that includes both Shawnee Park and 34th Street. Such findings suggested a need for localized investigation and potential interventions in the Shawnee Park area, an opportunity that would have been delayed or missed completely by relying on clinical data alone.

As the full potential of wastewater surveillance for Covid-19 begins to be realized, its advantages are increasingly appreciated by the public health community and the general public. As a leading indicator, it can alert communities to the presence of new variants or an imminent surge in clinical cases. Wastewater monitoring is cost-effective, anonymous, and passive. It is not dependent on access to health care. It provides a more timely, equitable, and representative picture of the level of virus circulating in a community than clinical data, because it encompasses data from individuals who:

• can be symptomatic, asymptomatic or presymptomatic
• cannot access testing
• choose not to test
• test at home and do not report their results

The epidemiological value of wastewater monitoring has been vividly demonstrated during the Covid-19 pandemic. The number of communities that are monitoring wastewater both in the U.S. and worldwide is increasing, though the practice is still more common in high income countries. Accessible data and increased participation of low-and middle-income countries will add additional value. While national programs are vital, local initiatives can provide important information to inform public health decisions. National and international partners can play a vital role in empowering local programs and providing targeted feedback to help assist workers on the ground. This collaboration can help provide rapid, equitable knowledge about the ongoing evolution of a pandemic on a global level. The Pandemic Prevention Institute is working with partners in Ghana, India, and two sites in Bangladesh to enhance wastewater testing in those countries.

Local disease surveillance has global impact, since lack of surveillance in one region can result in the emergence and unmonitored spread of viral variants and new pathogens that endanger the rest of the world. Wastewater surveillance will play an increasingly important role in controlling outbreaks of SARS-CoV-2, as well as future, as yet unknown, pathogens, thus helping to prevent the next pandemic.