Wastewater-based epidemiology (or wastewater-based surveillance or sewage chemical-information mining) analyzes wastewater to determine the consumption of, or exposure to, chemicals or pathogens in a population. This is achieved by measuring chemical or biomarkers in wastewater generated by the people contributing to a sewage treatment plant catchment. Wastewater-based epidemiology has been used to estimate illicit drug use in communities or populations, but can be used to measure the consumption of alcohol, caffeine, various pharmaceuticals and other compounds. Wastewater-based epidemiology has also been adapted to measure the load of pathogens such as SARS-CoV-2 in a community. It differs from traditional drug testing, urine or stool testing in that results are population-level rather than individual level. Wastewater-based epidemiology is an interdisciplinary endeavour that draws on input from specialists such as wastewater treatment plant operators, analytical chemists and epidemiologists. History The first documented use of WBE came in 1954, in a study of schistosome of snails. Wastewater-based epidemiology thereafter spread to multiple countries. By the turn of the 21st century, numerous studies had adopted the technique. A 2005 study measured cocaine and its metabolite benzoylecgonine in water samples from the River Po in Italy. Wastewater-based epidemiology is supported by government bodies such as the European Monitoring Centre for Drugs and Drug Addiction in Europe. Similar counterparts in other countries, such as the Australian Criminal Intelligence Commission in Australia and authorities in China use wastewater-based epidemiology to monitor drug use in their populations. As of 2022, WBE had reached 3,000 sites in 58 countries. A group of Chinese scientists published the first WBE study on SARS-CoV-2 in 2020. They assessed whether the virus was present in fecal samples among 74 patients hospitalized for COVID-19 between January 16 and March 15, 2020 at a Chinese hospital. The first US SARS-CoV-2 study came from Boston. It reported a far higher rate of infection than had been estimated from individual PCR testing. It also served as a warning system, alerting the public to outbreaks (and outbreak ends) before positive test rates changed. However, considerable variability has been found within populations, based on symptom profiles, which may compromise measurement accuracy as the pathogen evolves. Technique Wastewater-based epidemiology is analogous to urinalysis on a community scale. Small molecule compounds consumed by an individual can be excreted in the urine and/or feces in the form of the unchanged parent compound or a metabolite. In communities with sewerage, this urine combines with