Wastewater is water that returns to the public utility system after it’s been used for purposes such as flushing a toilet, bathing, washing dishes, etc. In wastewater surveillance, public health officials collect sewer system samples underneath specific buildings or water treatment plants —to test for infectious pathogens like SARS-CoV-2, hepatitis or parasites. It is also used to detect illicit drugs and changes in dietary patterns. Wastewater surveillance has been around since 1954 when epidemiologists in South Africa began using it to detect parasites contaminating local drinking water. Currently, around 58 countries use wastewater surveillance as part of public health efforts, according to the CDC.
Wastewater testing has been an important pandemic tool for tracking COVID-19 cases in addition to laboratory testing of cases because it is an early indicator of rising or falling cases. Around a third to half of people infected with SARS-CoV-2 shed the virus in feces providing a leading indicator — by about one to four days — that cases and hospitalizations are going to rise or fall. For example, the coronavirus identified in Boston’s wastewater increased before Boston’s Omicron case numbers did, and then went down before case numbers did. Missouri’s wastewater surveillance system — which includes genetic sequencing for variants — identified Delta cases last summer weeks before laboratory testing did, according to COVID-19 Data Dispatch.
In February 2022, the CDC added a wastewater tracking data system to its COVID-19 tracking dashboard.