"Wastewater is a good way to track COVID because essentially everybody poops," said Dr. Isaac Ghanni, CDPH Medical Director Testing-Laboratory Based Surveillance. "If you have COVID there will be some in stool and if we test wastewater we can hopefully find it."
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It's been especially helpful since COVID testing is not always reliable.
"Many of these rapid tests you can buy over the counter, they are not reported to public health so this is a way to approximate all those people," Ghanni explained.
The samples are collected from Chicago's water treatment plants and from seven community locations. All the data is submitted to the CDC. On Friday, the federal agency added wastewater data to its national COVID tracker.
"It's meant to be an additional extra piece of information that we can access with the rest of our data points and have a better understanding of the pandemic," said Ghanni.
The data is used to compare trends or back up what is being reported in case counts.
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"Some places we get a little bit of lead time so seeing increases before clinical cases and some places it matches," said Dr. Rachel Poretsky, UIC.
The data has been used to prepare public health officials on where to deploy resources.
"They'll do things like deploy mobile vaccination clinics or they can increase testing frequency or more availability," Portesky said.
Wastewater samples are also being used to sequence the virus in order to look for new variants.
While wastewater samples have been helpful when used collectively with other data, public health officials said there is more scientific work to do before wastewater surveillance can be relied on as a true reflection of cases.