Farkas, K., Hillary, L. S., Malham, S. K., McDonald, J. E., & Jones, D. L. (2020). Wastewater and public health: the potential of wastewater surveillance for monitoring COVID-19. Current Opinion in Environmental Science & Health.
The facts and figures of COVID-19
In December of 2019, an outbreak of the novel pathogenic virus SARS-CoV-2 was reported in Wuhan, China and has since taken the world by storm. As of June 2020, over 6 million cases and 376,000 deaths have been confirmed. The highly infectious nature of the COVID-19 virus, as well as its tendency to present with mild or even no symptoms in patients, have led to clinical and economic struggles worldwide. These unique traits call for a need to think outside of the box when attempting to monitor and mitigate the toll that the virus takes on communities.
Turning to an unlikely place for answers
Recent research efforts have investigated wastewater as a possible tool for modeling the spread of COVID-19 in urban environments. Evidence of pathogenic viruses in humans can be found in their feces and urine, both of which make up a large portion of residential wastewater. Viruses excreted through these routes enter the wastewater environment as they are flushed down toilets and sent to household septic systems or wastewater treatment plants. Although SARS-CoV-2 is an “enveloped” virus, meaning that it becomes inactivated shortly after leaving its host body, traces of the virus have been found in wastewater. By monitoring changes in the concentration of the virus in residential wastewater, researchers may be able to better understand and model how COVID-19 impacts residential communities.
Many different methods employ wastewater as a tool for virus surveillance. One relatively simple and cost-effective method involves centrifuging, in which a wastewater sample is put in a small vial and spun rapidly until gravity forces the separation of materials of differing weights, and/or filtering wastewater so that any virus present becomes concentrated and can then be analyzed. Although this method is fairly user-friendly, its time-consuming nature means precludes its ability to analyze a large number of samples. Molecular analysis can also be used to specifically target the genetic material of SARS-CoV-2, allowing researchers to identify and quantify the virus in wastewater. Although other materials found in wastewater (such as organic contaminants) sometimes interfere with molecular analysis, this method is capable of rapidly processing large numbers of samples. Methods involving molecular analysis of multiple viruses at once, also known as viral metagenomics, could also help address the question of whether or not coinfection influences the outcome of COVID-19 cases. Several studies that have utilized the tools in this wastewater monitoring toolbox have observed significant correlations between the concentrations of SARS-CoV-2 in wastewater and the number of COVID-19 cases in the communities assessed (1; 2; 3).
Is wastewater actually part of the problem?
Although recent studies have observed that wastewater treatment significantly decreases SARS-CoV-2 concentrations in wastewater, reports also suggest that residual virus present in wastewater may infect secondary hosts in aquatic environments close to wastewater outlets. However, researchers point out that due to the virus’ instability in water as well as the significant dilution that takes place due to these waterbodies’ large volumes of water, human contraction of the virus from shellfish and/or bathing waters from these environments is very unlikely.
Looking to the future
Despite continued efforts to monitor the number of people affected by COVID-19, researchers suggest that the number of asymptomatic cases has resulted in an exclusion of approximately 80% of transmissions. This study points out that calculating the exact number of COVID-19 cases in a community based solely on virus concentrations in wastewater is nearly impossible. However, by relying on wastewater surveillance, we may eliminate some of the guesswork involved in approximating COVID-19’s impact on the population.