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 Holland, KWR’s researchers believed that the coronavirus SARS-CoV-2 could be found in sewage water from the stools of infected people. Since then, microbiologists have been working to detect the new coronavirus in wastewater treatment plants and on March 15 their preliminary results detected the virus gene fragments of SARS-CoV-2.
We spoke with Prof. Gertjan Medema, Principal Microbiologist at KWR, to find out a bit more about their latest research and what their results mean for the global wastewater industry.
Question: KWR is testing wastewater for SARS-CoV-2 to get an indication of the number of virus infections in the population. Do you think testing wastewater for the coronavirus SARS-CoV-2 is more efficient than the traditional testing methods?
Answer: Wastewater testing is a proxy method which can provide indirect information about the occurrence of the virus in a population connected to a given wastewater treatment plant (WWTP). Obtaining a number of infected people is currently not possible as we do not know how much virus each individual will release in its excretion (e.g., faeces). This might however become possible with future research, in particular if wastewater data is combined with clinical and epidemiological data (e.g., number of diagnosed or hospitalized people). Nevertheless, as you have been able to read across the media in the last weeks, conventional testing does not tell you how many people are really infected, because it is impossible to test the whole population. This is because: i) the number of tests available is limited and only the most severely affected people are tested and ii) not everybody will have symptoms severe enough to get in contact with health services (and hence get tested). This means that there is a lack of information about the prevalence of the virus in the general population. This is where wastewater surveillance, which is often referred to as “wastewater-based epidemiology”, 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. Conventional methods (i.e., testing individuals directly) will remain crucial as they are the only way health authorities have to determine if individuals are infected. Testing wastewater can complement this information by allowing 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 also provides spatial information, in the sense that large areas where the virus might not have been detected yet through conventional testing can be rapidly screened via wastewater testing. Last but not least, wastewater testing could be 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.
Obtaining a number of infected people is currently not possible as we do not know how much virus each individual will release in its excretion
Q: Is KWR currently testing all wastewater plants in The Netherlands?
A: KWR has been carrying out a pilot study in a selected number of WWTP, yet we are currently trying to setup a national monitoring program together with other partners and the Dutch government.
Q: Is KWR working with other organizations in The Netherlands such as RIVM?
A: With regards to the results published so far, KWR and the RIVM conducted two independent studies, which however both showed that SARS-CoV2, the virus associated with COVID-19, can be detected in the influent of WWTP.
KWR and the RIVM conducted two independent studies, which however both showed that SARS-CoV2, the virus associated with COVID-19, can be detected in the influent of WWTP
Q: In the research, KWR mentions that “using this method, we might also be able to measure whether the number of virus infections in a city will increase again next winter.” Could you explain this idea further?
A: As mentioned in my previous answer (point 1), wastewater testing is an effective tool for rapid screening of communities and large populations. 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.
It could be possible to detect the reappearance of the virus at a very early stage, with obvious advantages for authorities
Q: According to the preliminary results of the report, could wastewater be a vector for the transmission of the coronavirus?
A: Wastewater has been shown to contain a large number of potentially harmful pathogens that are transmitted via the water cycle, such as norovirus and hepatitis A virus. SARS-CoV2, 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. Based on what we know of the shedding and spread of SARS-CoV2 and other coronaviruses, we consider the risk for sewage workers to be low (ref News KWR). Also, WHO has issued statements to this effect. Of course, existing safety measures should be followed to guarantee security and these are still valid and considered sufficient (ref STOWA, RIONED).
SARS-CoV2, as other coronaviruses, are not spread via the water cycle, because they are not as resistant to the environmental conditions in sewage
Q: Lastly, how should wastewater workers protect themselves adequately?
A: As mentioned above, in the Netherland, existing measures are deemed sufficient to protect WWTP workers from being infected by any pathogen potentially present in wastewater.
