As COVID-19 testing sites close and experts warn that case numbers are capturing a small minority of infections, many public health experts are turning to a newer source that might tell us what’s going on with the virus: our poop.

taking a photo

In the past two years, scientists have developed systems that can detect COVID-19 in our wastewater. This is a great early warning system, since the virus can show up in people’s waste days before they begin to experience symptoms or are able to get tested. It’s also less biased than case data: Not everyone can find a COVID-19 test and not every positive result will get reported … but everybody poops.

As with so many other COVID-19 metrics, however, interpreting wastewater data is not as simple as it seems. Before COVID-19, this type of data hadn’t been used to track respiratory viruses. This means the Centers for Disease Control and Prevention has little established infrastructure to build upon. The agency is attempting to standardize reporting from researchers across the country, many of whom have different water sampling methods. Plus, the state and local health officials who cite wastewater as a potential replacement for underreported case numbers aren’t used to interpreting data from the environment, which has unique caveats and requires a learning curve for those used to looking at numbers from hospitals and health clinics.

The Documenting COVID-19 project surveyed 19 state and local health agencies, as well as scientists who work on wastewater sampling, to learn about the challenges they’re facing. We found that many states are months away, if not longer, from being able to use wastewater data to guide public health decisions, even as the rise of an omicron subvariant, BA.2, looms. Meanwhile, the CDC’s highly shared wastewater surveillance dashboard is a work in progress and is difficult to interpret for users who might hope to follow the trends in their areas.