Coronavirus experts say the United States may face a second wave of cases after states reopen or in the fall or winter, when other viruses tend to flourish.
Detecting a new wave of cases can be hard with COVID-19’s relatively long incubation period and low testing rates in many states, including Iowa. This has prompted scientists to look for other detection methods.
One idea is a sewage study, in which scientists take samples from municipal wastewater systems to see whether there are traces of COVID-19 in feces, which would reveal the virus’s presence in the population.
Kelly Baker, an assistant professor of occupational and environmental health in the University of Iowa’s College of Public Health, studies sanitation and clean water. She weighed in on whether a sewage study would work to detect COVID-19 in a population.
Q: How does a sewage study work in terms of identifying illnesses in a community?
A: “It can provide you information about emergence of diseases or persistence of diseases at the community level. It doesn’t tell you how many people are infected, but it does tell you whether or not there is a health issue.”
Q: How do you do a sewage study?
A: “It depends on what the wastewater or sewage system in your community looks like. Some clear obvious points for samples would be at the end point in the system, the sewage treatment storage facility. You would want to take samples before they ever begin the treatment process. But you can also test wastewater upstream from there, where sewage lines are emerging out of individual communities. That can help you narrow down where you have one or more people shedding something of concern into the environment.”
Q: Have sewage studies been used elsewhere?
A: “There are a couple of studies in Europe that used sewage epidemiology to get at illicit drug use. It has been used to see whether there are antimicrobial-resistant bacteria being shed by people in a community. The Gates Foundation is investing in it for polio tracking. It’s been used for communicable and non-communicable diseases.”
Q: Has it been used to detect COVID-19?
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A: “It’s not been used for COVID yet, partly because so many of the resources are being used for the clinical diagnostic crisis. Also, it’s only been a couple of weeks ago a study was published out of China proving that COVID is being shed in human feces.”
Q: Would sewage epidemiology work for COVID?
A: “There is a research gap between knowing COVID can be secreted by human feces and water monitoring. A lot of the environmental literature suggests COVID-19 doesn’t last long in the environment. There’s no research I’m aware of at this moment that tracks how long the virus stays alive in feces or water. This is kind of a critical thing that has to happen for wastewater monitoring to be useful. If it doesn’t last long, we can sample at wastewater treatment plants a lot and not detect it (COVID-19) because it’s dead.”
Q: Are there other challenges of this type of study?
A: “Another limitation of sewage epidemiology is the dilution factor. If you only have 11 to 12 percent of the people testing positive, there are another 88 to 90 percent of the people also using sewage and wastewater systems that don’t have COVID. All that gets mixed together, which then dilutes the concentration of any virus being shed by the infected groups. An upstream testing system would be useful in terms of increasing your chance of capturing any concentrated virus in the water.”
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