March 11 marks five years since the World Health Organization declared the COVID-19 virus officially a pandemic. Tracking the virus has been key to understanding where outbreaks are occurring and one tracking tool that had been mostly on the shelf prior to the pandemic is wastewater surveillance. That’s pretty much what it sounds like — testing what we flush down the toilet which eventually lands in what’s known as a sewer shed. Marketplace’s Stephanie Hughes spoke with molecular virologist Marc Johnson at the University of Missouri about the advantages of wastewater surveillance. The following is an edited transcript of their conversation.