Wastewater-based epidemiology
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 other wastes including other individuals' urine as they travel to a municipal wastewater treatment plant. The wastewater is sampled at the plant's inlet, prior to treatment. This is typically done with autosampler devices that collect 24-hour flow or temporally composite samples. These samples contain biomarkers from all the people contributing to a catchment. Collected samples are sent to a laboratory, where analytical chemistry techniques (such as liquid chromatography-mass spectrometry) are used to quantify compounds of interest. These results can be  expressed in per capita loads based on the volume of wastewater. Per capita daily consumption of a chemical of interest (e.g. a drug) is determined as formula_1 where "R" is the concentration of a residue in a wastewater sample, "F" is the volume of wastewater that the sample represents, "C" is a correction factor which reflects the average mass and molar excretion fraction of a parent drug or a metabolite, and "P" is the number of people in a wastewater catchment. Variations or modifications may be made to C to account for other factors such as the degradation of a  chemical during its transport in the sewer system. Applications. Commonly detected chemicals include, but are not limited to the following; Temporal comparisons. By analyzing samples taken across different time points, day-to-day or longer term trends can be assessed. This approach has illustrated trends such as increased consumption of alcohol and recreational drugs on weekends compared to weekdays. A temporal wastewater-based epidemiology study in Washington measured wastewater samples in Washington before, during and after cannabis legalisation. By comparing cannabis consumption in wastewater with sales of cannabis through legal outlets, the study showed that the opening of legal outlets  led to a decrease in the market share of the illegal market. Spatial comparisons. Differences in chemical consumption amongst different locations can be established when comparable methods are used to analyse wastewater samples from different locations. The European Monitoring Centre for Drugs and Drug Addiction conducts regular multi-city tests in Europe to estimate the consumption of illegal drugs. Data from these monitoring efforts are used alongside more traditional monitoring methods to understand geographical changes in drug consumption trends. Virus surveillance. Sewage can also be tested for signatures of viruses excreted via feces, such as the enteroviruses poliovirus, aichivirus and  coronavirus. Systematic wastewater surveillance programs for monitoring enteroviruses, namely poliovirus, was instituted as early as 1996 in Russia. Wastewater testing is recognised as an important tool for poliovirus surveillance by the WHO, especially in situations where mainstream surveillance methods are lacking, or where viral circulation or introduction is suspected. Wastewater-based epidemiology of viruses has the potential to inform on the presence of viral outbreaks when or where it is not suspected. A 2013 study of archived wastewater samples from the Netherlands found viral RNA of Aichivirus A in Dutch sewage samples dating back to 1987, two years prior to  the first identification of Aichivirus A in Japan. During the COVID-19 pandemic, wastewater-based epidemiology using qPCR and/or RNA-Seq was used in various countries as a complementary method for assessing the load of COVID-19 and its variants in populations. Regular surveillance programs for monitoring SARS-Cov-2 in wastewater has been instituted in populations within countries such as Canada, UAE, China, the Netherlands, Singapore, Spain, Austria and the United States. As of August 5, 2020, the WHO recognises wastewater surveillance of SARS-CoV-2 as a potentially useful source of information on the prevalence and temporal trends of COVID-19 in communities , while highlighting that gaps in research such as viral shedding characteristics should be addressed.