News Release

Levels of Covid-19 in Wastewater Rise Across the US


Experts are cautioning that levels of Covid-19 in wastewater are increasing in many cities across the country. Surveillance of US wastewater sites had shown consistent declines in levels of Covid-19 across most cities in the country for the last several weeks, mirroring the decrease in cases after the first Omicron surge. The data is now showing a reversal. According to an analysis of Centers for Disease Control and Prevention data by Bloomberg, “more than a third of the CDC’s wastewater sample sites across the US showed rising Covid-19 trends in the period ending March 1 to March 10.” Bloomberg analyzed data from more than 530 sewage monitoring sites; out of those sites, “59% showed falling Covid-19 trends, 5% were roughly stable, and 36% were increasing [over a 15-day period].” The CDC’s aggregated wastewater data and an explanation can be found here.

JULIA RAIFMAN, ScD, SM,, @JuliaRaifman 
    Raifman is an Assistant Professor of Health Law, Policy & Management at Boston University. She conducts research on health and social policies drivers of population health and health disparities. 

The decline in reliable case counting from reported tests has made community wastewater surveillance increasingly necessary. Dr. Raifman says: “People can shed the virus in their digestive tracts before they become symptomatic. Wastewater tracking can detect trends in Covid-19 cases before people develop symptoms and get tested, allowing time for a swift response.

“We always have to make decisions in the context of uncertainty, and should look to a rise in [Covid-19 levels in] wastewater as a signal to look closely at other indicators and be prepared to respond quickly if there are signs of a surge. A fast response is especially important in settings with high exposure, crowded indoor settings, like schools and workplaces. Every day counts with exponential spread; every case averted can reduce several other cases.

“An early warning is most helpful if policymakers use it to inform actions to reduce the surge, like implementing mask mandates to reduce transmission and letting people know that a surge is coming, to get vaccinated and boosted as soon as possible, and to take additional precautions. Many of the harms that occur during surges can be reduced by policymakers taking early action to reduce transmission. The United States had at least 63% more deaths than other high-income countries during the Omicron BA1 surge, which killed more than 150,000 people, including hundreds of children, in weeks. Early action could help reduce a similar toll in a BA2 surge, which looks like it could happen in the US based on wastewater trends and surges in several European countries. We see wastewater [Covid-19 levels] increasing in 37% of sites currently.

“To improve surveillance and equity, it is important to increase the number of wastewater surveillance sites. We also need further information on wastewater trends, levels, and validity in different contexts and how we interpret absolute values and trends, along with complementary types of data.”

The CDC’s aggregated data for wastewater surveillance, March 24