“The sewer is the conscience of the city. Everything there converges and confronts everything else. In that livid spot there are shades, but there are no longer any secrets.” Victor Hugo – “Les Miserables”
To get a sense of the prevalence of COVID-19 in a community you need to test hundreds to thousands of people. This is difficult, resource intensive, and requires cooperation for testing among people both with and without symptoms.
In various locations from China to medieval London, there have been attempts to utilize human excrement for the betterment of mankind, from employing it as fertilizer to processing it to make gunpowder. Such attempts did not always work as planned. The use of sewage for fertilizer in Europe and the United States in the 1840s and 1850s led to the spread of waterborne diseases, including cholera and typhoid. As the importance of sanitary elimination of human waste became ever clearer, ideas and technology for our modern system of sewage management evolved. We have since advanced a great deal, so that all industrialized nations now have a well-developed system for clean water entry, as well as sewage treatment and disposal. Nonetheless, there remains a nagging question of whether human waste could be used for something productive.1
In the early 2000s, SCIM was developed as a technique to assess population-level human health and disease. In SCIM, untreated sewage is tested for a chemical of interest which reflects a health parameter for a community. Chemicals of interest and usage rates can be calculated for substances as varied as opioids, tobacco, pesticides, and even nonnutritive sweeteners. For instance, relative opioid use can be calculated over time for a given “sewershed” or sewage catchment area. The calculation of community-wide exposure to substances as a means of getting real-time data on shifts of usage without having to collect and collate data from thousands of individuals has been termed wastewater-based epidemiology.
We use urine and stool testing in so many other areas, such as urinalysis, urine drug testing, urine Legionella antigen testing, and stool testing for common pathogens. What a rich source of information is present in the combination of urine and stool that collectively make up sewage! With the average volume of urine per adult being approximately 1 liter daily (and with urine calculated to be approximately 1% of wastewater), accurate analytic techniques can estimate per capita exposure to different substances. Applications of wastewater-based epidemiology have included tracking community prevalence of enteric viral infections, opioid and tobacco use, and many other indicators of health and disease.2
Given the enormous work in the field over the last 2 decades and that SARS-CoV-2 RNA has been detected in feces of both symptomatic and asymptomatic patients, it was only a short conceptual step for those familiar with sewage epidemiology to consider adapting it to assess the prevalence of COVID-19 in a community.
An elegant study collected untreated sewage from southeast Queensland, Australia. The sewage was processed, concentrated, and then tested with reverse transcriptase polymerase chain reaction analysis for SARS-CoV-2 RNA. The number of RNA copies was then entered into an equation that included the population served by the sewage encatchment area, as well as the measured liters of wastewater and grams of feces per day. This provided an estimate of the number of persons infected in the community, and the researchers were able to show reasonable agreement between the numbers estimated by sewage analysis and that found in traditional clinical testing.3,4
The promise of wastewater-based epidemiology is large. Early research indicates that quantification of viral particles in sewage can be accurately assessed and correlated with the prevalence of the infection in the community. Such levels can then be used to track infection rates of COVID-19 over time, as well as to compare the relative rates in different communities.
Our sewage may hold the answer to accurately and easily tracking COVID-19, and ultimately help us gain a better hold on this disease.
Dr. Notte is a family physician and chief medical officer of Abington (Pa.) Hospital–Jefferson Health. Follow him on Twitter (@doctornotte). Dr. Skolnik is professor of family and community medicine at Sidney Kimmel Medical College, Philadelphia, and associate director of the family medicine residency program at Abington (Pa.) Hospital–Jefferson Health. They have no conflicts related to the content of this piece.
1. History of water supply and sanitation. Wikipedia, https://en.wikipedia.org/wiki/History_of_water_supply_and_sanitation.
2. Daughton C. Monitoring wastewater for assessing community health: Sewage Chemical-Information Mining (SCIM). Sci Total Environ. 2017 Nov 29. doi: 10.1016/j.scitotenv.2017.11.102.
3. Ahmed W et al. First confirmed detection of SARS-CoV-2 in untreated wastewater in Australia: A proof of concept for the wastewater surveillance of COVID-19 in the community. Sci Total Environ. 2020 Apr 18. doi: doi.org/10.1016/j.scitotenv.2020.138764.
4. Daughton C. The international imperative to rapidly and inexpensively monitor community-wide COVID-19 infection status and trends. Sci Total Environ. 2020 Mar 23. doi: 10.1016/j.scitotenv.2020.138149.