The Centers for Disease Control and Prevention has once again elevated Chicago and cook County’s COVID-19 threat level to high. But just how reliable are the COVID-19 case numbers? An effective response to the COVID-19 resurgence requires high-quality, real-time data. Yet public health officials have been warning that it is impossible to know with certainty how widespread the latest resurgence may be.

Loss of federal funding has led to COVID-19 testing site closures throughout Illinois, and the nation. Milder symptoms for those who are vaccinated and increased use of at-home rapid tests, which people rarely report to health authorities, means accurate COVID-19 data is increasingly hard to come by. 

As pandemic data collection is increasingly questioned and criticized, some scientists are turning to sewage for solid answers. Wastewater epidemiology can provide useful information about COVID-19’s resurgence and clues about what to expect in coming months.

University of Illinois at Chicago associate professor Rachel Poretsky is doing sewage surveillance through the University of Illinois’ Discovery Partners Institute. Poretsky is co-leading a team with computer scientist Charlie Catlett that’s using Chicago wastewater to identify viral hot spots. “When there’s incomplete data, or holes in the data, that’s when wastewater data is really useful,” said Poretsky. “At each stage of the pandemic there were citywide and nationwide testing challenges. There were often months without tests, or the wrong tests or extremely long waits to get appointments.”

Poretsky and Charlie Catlett came up with a creative, low-cost solution to capturing more accurate pandemic data. A tampon is placed inside a small protective cage and lowered into a city sewer. Twice a week the maintenance hole is lifted, the cage is removed, and its contents are collected. So far, the data they’ve collected correlates closely with public health data for Chicago.  

Poretsky and Catlett have been doing Chicago sewage surveillance since 2020 and are hopeful the data they’re collecting will prove useful in tracking future infectious diseases, playing an important role in public health. “We save a small vial of each sample we collect. That’s creating all kinds of records of what’s happening in our city,” said Catlett. “Because we weren’t collecting sewer samples in 2019, we don’t know when COVID first showed up. The records we’re keeping now will be helpful for future outbreaks and diseases.”