As the faeces from infected patients entered the sewage system, the virus has been found in raw sewage. According to the U.S. Centres for Disease Control and Prevention, it is not known whether this virus can cause disease if a person is exposed to untreated wastewater, but the risk of transmission of the virus that causes COVID-19 through properly designed and maintained sewerage systems is thought to be low. Furthermore, standard practices associated with wastewater treatment plant (WWTP) operations should be sufficient to protect wastewater workers from the virus.
Wastewater-based epidemiology (WBE) is a rapidly developing discipline that analyses certain pollutants and biomarkers such as pharmaceuticals, illicit drugs or pathogens in raw wastewater. Research on the presence of the novel coronavirus in wastewater is underway across the world, in an attempt to monitor the presence of the virus in communities.
It is generally regarded as a complement to directly testing individuals, limited in most countries because of resource constraints. Also, asymptomatic carriers are often not tested. This is where WBE comes in to provide additional information on the spread of the virus. It can provide an early warning of the possible re-emergence of the virus. Immediate applications include informing policy regarding disease control measures, and effective targeting of investment and efforts to control the pandemic.
Researchers worldwide are carrying out studies to monitor the presence of SARS-CoV-2 genetic material at WWTPs. Reverse transcription polymerase chain reaction assays (RT-PCR) are used to measure the amount of SARS-CoV-2 RNA in wastewater. Some institutions involved in this type of research include the KWR water research institute in the Netherlands, Cranfield Water Science Institute in the UK, the University of Arizona Water and Energy Sustainable Technology Center, Arizona State University, the University of Queensland and Australia's national science agency CSIRO, the University of Otago in New Zealand, and Ben-Gurion University in Israel, among others.
The novel coronavirus has been detected in raw wastewater, but not after treatment. Based on current knowledge, it does not spread via the water cycle, and most water treatment routines are thought to kill or remove coronaviruses effectively in wastewater. However, there have been calls for additional research on the fate of the virus in the urban water cycle, noting that the effectiveness of sewage treatment methods has not been studied specifically for SARS-CoV-2.
Many questions still need answers, and scientists from different fields should join forces with governments and public utilities to address this critical public health issue. Michigan State University (MSU) water expert Joan Rose is leading efforts to collaborate with scientists worldwide, as chair of the COVID-19 Task Force for the International Water Association (IWA). Indeed, collaboration is a mainstay of plans for surveillance programmes being planned by several countries. Other coronaviruses have shown seasonality, so scientists warn that systems must be established to stay vigilant and prevent a potential return. Wastewater monitoring data can be integrated with health data to provide a powerful tool for decision-makers. Wastewater surveillance could be particularly useful for monitoring likely hot spots for new coronavirus entry and dispersion such as airports.
In the future, scientists hope to use WBE to not just detect the geographic regions where COVID-19 is present, but to approximate the number of people infected without testing every individual in a location. There are many unknowns to get to that point. At the moment, researchers use molecular methods to obtain a number of gene copies per litre, which may depend on many factors: the extent of viral shedding in the faeces of infected individuals, the type of wastewater arriving to a WWTP (domestic, industrial, stormwater), degradation of the viral RNA, sampling methods, etc.
Moreover, it is not known yet if the virus remains contagious in sewage. Wastewater studies done so far use molecular assays that detect the genetic material of SARS-COV-2, but not the presence of the structurally intact virus or its infectivity. Infectivity (virus viability) may be determined via cell culture methods. Virus growth in cell culture indicates the potential for the virus to replicate in humans and cause disease. Because these methods require Biosafety Level 3 measures, many studies only include molecular assays. It may be that wastewater contains only non-infectious SARS-CoV-2 or just its genetic material.
Clearly, further research is needed to know the implications of the presence of the virus in wastewater, with knowledge gaps concerning the occurrence and survival of SARS-COV-2 in wastewater, as well as the removal by treatment processes. Next, we feature two interviews (you can read the full version in the Smart Water Magazine website) with scientists at the forefront of this research.
Professor Gertjan Medema, (KWR): "SARS-CoV2, as other coronaviruses, are not spread via the water cycle"
Professor Gertjan Medema, Principal Microbiologist at KWR
The Dutch water research institute KWR has been testing substances in urban sewage water for almost ten years. When the coronavirus outbreak began and before the first case was announced in the Netherlands, KWR’s researchers believed that the coronavirus SARS-CoV-2 could be found in sewage water from the stools of infected people, and have been working since then to detect it in wastewater treatment plants (WWTP).
Currently, there is a lack of information about the prevalence of the virus in the general population. Professor Gertjan Medema, Principal Microbiologist at KWR, explains that wastewater surveillance can help “health authorities monitor, on a population level, the occurrence of the virus and, indirectly, give an indication about whether people are still infected.” This type of information allows authorities “to monitor the occurrence of the virus in large populations over time, which is crucial if one seeks to determine the effect of measures taken to reduce its spreading.”
Furthermore, it is “an ideal tool to determine if the virus and the epidemy are resurfacing, giving authorities time to identify locations where it is spreading and allow them to setup all the necessary measures to contain it”, notes Professor Medema. “This means that if wastewater of a city (or multiple ones) is monitored continuously (or at regular intervals) in the months to come, it could be possible to detect the reappearance of the virus at a very early stage, with obvious advantages for authorities”. He clarifies that “obtaining a number of infected people is currently not possible as we do not know how much virus each individual will release in their excretion (e.g., faeces)”.
KWR has been carrying out a pilot study in a selected number of WWTP. Preliminary results detected gene fragments of SARS-CoV-2 in the influent of several plants as early as March. Efforts are under way to setup a national monitoring program together with other partners and the Dutch government. Professor Medema stresses that “SARS-CoV-2, as other coronaviruses, are not spread via the water cycle, because they are not as resistant to the environmental conditions in sewage as the noro- and hepatitis A viruses”.
The risk for sewage workers is considered to be low. As Professor Medema emphasizes, “existing safety measures should be followed to guarantee security and these are still valid and considered sufficient”. They ensure protection for WWTP workers from being infected by any pathogen potentially present in wastewater.
Dr Zhugen Yang, Cranfield Water Science Institute: "Testing wastewater can provide early warning of infections in the community"
Dr Zhugen Yang, Lecturer in Sensor Technology at Cranfield Water Science Institute.
Scientists at England’s Cranfield University are working on a new test to detect SARS-CoV-2, the virus responsible for COVID-19, in the wastewater of communities infected with the virus. They propose rapid testing kits using paper-based devices to detect biomarkers in faeces and urine from disease carriers that enter waste water streams. The kits can be used on-site at waste water treatment plants.
Dr Zhugen Yang, Lecturer in Sensor Technology at Cranfield Water Science Institute, and head of this research, explains their method of testing: “As it is folded and unfolded, the sensor filters the nucleic acids of pathogens, which then react with preloaded reagents to reveal the presence of certain infections. The results can be seen with the naked eye, presenting as a green circle when positive.” The method has several advantages: “This device is cheap (costing less than £1 (US$1.25)) and will be easy to use for non-experts after further improvement.”
Dr Yang sais his team at Cranfield university have not tested wastewater in England yet, as their labs at the university had to close due to the pandemic. “However, we have already shown that our paper device is able to test nucleic acid in sewage for a proof-of-concept study,” he reports.
The advantage of testing wastewater, explains Dr Yang, is it can provide an early warning of infections in the community: “This will significantly help governments to take proper prevention and effective intervention measures. Currently the test is designed as a rapid and cost-effective diagnostic tool for the mass population rather than individuals.” Furthermore, he thinks that “these testing kits could also be used for individual diagnosis of SARS-CoV-2 with further development, as has been proved for malaria testing.”
Cranfield University is working with other organizations and governmental bodies on this study: “At the moment, we have been sponsored by the UK’s Natural Environment Research Council and Royal Academy of Engineering, which is enabling us to further improve the performance of the device. We have been approached by a water company for discussion on collaboration.”
A key issue is the potential of wastewater to be a vector for the transmission of the coronavirus. In this regard, Dr Yang thinks “Currently it’s difficult to say, but there is evidence to show that viral RNA of COVID-19 has been detected. It will also depend on the pandemic; as more people become infectious, a higher dose of COVID-19 may be present in sewage.”