Tom Richard, director of the Institutes of Energy and the Environment, explained that although wastewater monitoring has many benefits, including enabling researchers to see whether SARS-CoV-2 is increasing or decreasing in a specific location, there are challenges in correlating the measured virus concentrations with the number of COVID-19 cases.
“Individuals shed more or less virus through their feces depending on the severity of their infection and how long they have been infected; the amount of shedding can vary from person to person by an order of magnitude,” he said. “Similarly, some people suffer from respiratory symptoms but never get the virus in their gastrointestinal systems. And while there is very little hard data about virus shedding patterns for people who are asymptomatic, indications are that some of those people are also shedding the virus.”
Exact correlations are also difficult because the number of people on campus and their water use fluctuates over the course of a day or week. For example, an increase in the concentration of virus detected in wastewater samples could mean there has been an increase in on-campus incidence, or it could mean that people are coming in from off campus and using the toilets because they are taking once- or twice-a-week in-person classes.
“All of these variables can substantially affect our inferences, so it’s important that we try to really understand them,” said Justin Silverman, assistant professor of information sciences and technology and a co-hire of the Institute for Computational and Data Sciences. To that end, Silverman is building statistical tools using techniques from a field called Bayesian time series analysis, to account for the variability and uncertainty in the system. “Our goal is to try to get a sense of what the concentration of the virus is at any given time from these very noisy data,” he said.
Silverman said he is consulting with researchers at other universities who are also attempting to set up wastewater monitoring programs. “I am making all of the modeling and tools that I am building available to anyone who can use them,” he said. “This is an extremely difficult task, and we are all better off when we share strategies that work.”
Laying the Groundwork
To collect the wastewater samples, the team first had to locate the sewer system access points from which to sample the wastewater. “Penn State has 18 miles of underground pipes, carrying about 1.6 million gallons of wastewater per day to the Wastewater Treatment Facility,” said Swisher. “There are 900 manholes to access this wastewater.”