SARS-CoV-2 virus in wastewater

T. G. Masaryk Water Research Institute together with the Research Institute of Veterinary Medicine in Brno, and with epidemiologists from the 1st Faculty of Medicine, Charles University, introduced a wastewater monitoring system in order to monitor the epidemic situation of the Covid-19 disease and predict its development. Monitoring is financed by the project VI04000017 "Use of wastewater monitoring as an early warning tool against the emergence of the epidemiological situation" programme 4. VS BV III. by institutional resources of the Ministry of the Environment through an internal TGM WRI grant 3600.52.33/2020. Sampling is performed by WWTP operators. The particular methodology was newly approved by the Ministry of Health of the Czech Republic.

What exactly do we monitor?

The principle of the system is the collection of untreated wastewater at selected wastewater treatment plants (WWTPs) suitable for the purpose, isolation of viral RNA, and quantitative detection of the number of the SARS-CoV-2 virus genomic units. Viral RNA is secreted into the wastewater by SARS-CoV-2 infected persons and therefore its amount correlates with their numbers in the areas connected to the monitored WWTPs. The results of the analyses show the good usability of the chosen method and thus the possibility of obtaining valuable objective epidemiological information at a disproportionately lower cost than with the help of clinical trials.

Where do we monitor?

The research team is currently performing continuous monitoring at four WWTPs in the Czech Republic and is analysing and evaluating the results of analyses of more than 550 samples taken at 66 WWTPs throughout the Czech Republic during all waves of the epidemic, and it is ready to offer cooperation to the healthcare sector for successful implementation of the European Commission recommendation on the introduction of systematic monitoring of SARS-CoV-2 in wastewater dated 17 March 2021. T.G. Masaryk Water Research Institute, p.r.i. ensures, independently or in cooperation with WWTP operators, wastewater sampling and, together with the Research Institute of Veterinary Medicine, p.r.i. in Brno, performs isolation and quantitative detection of SARS-CoV-2 RNA from wastewater in three laboratories.

Course of the coronavirus epidemic in municipal wastewater?

The obtained results confirmed that the system is able to detect the onset of a new wave of the epidemic before it is proven by clinical tests. Ongoing regular monitoring of SARS-CoV-2 virus RNA in wastewater in 4 cities of the Czech Republic (Prague, Brno, Kladno, and Břeclav) at 5 WWTPs (Prague WWTP – the existing and the new water line, Brno WWTP, Vrapice-Kladno WWTP, and Břeclav WWTP) is a unique tool that allows capturing the current state of the occurrence of the coronavirus in the Czech Republic and the expected onset of the next epidemic wave. Wastewater monitoring is thus a functioning objective tool for monitoring the development of the virus in the population, which does not require testing of individuals.

The RNA monitoring of the SARS-CoV-2 coronavirus in wastewater, carried out since April 2020, captured the individual waves of the covid-19 epidemic in the Czech Republic and can thus be considered a functioning marker of the occurrence of covid-19 in the population.

Objective data obtained from wastewater monitoring show that the almost complete elimination of the virus in summer 2021 was followed by a sequence of waves of increased occurrence of GE (genome units) of the SARS-CoV-2 virus in wastewater, correlated with the number of persons tested positive for covid-19, detected by PCR tests.

The ratio of the viral load of wastewater to the number of positive tests changed at the beginning of summer 2022, i.e. the virus was present in the population, but did not significantly affect the health of the population.

The situation at the end of autumn 2022 shows stagnation in the occurrence of the covid-19 marker in wastewater in most samples, accompanied by a decrease in the number of people tested positive. The situation shows that there is no development of the originally started autumn epidemic wave.

Based on the progress so far, it can be assumed that in the population of the Czech Republic there will be alternating waves of increased occurrence of the virus in the population without a significant effect on public health and their gradual stabilization at the level of the occurrence of common infectious diseases with the probability of the onset of an epidemic only in the case of a new variant of the virus.

Two-year wastewater monitoring showed the adaptation of the population of the Czech Republic to the presence of the SARS-CoV-2 virus.

And what the fresh results show (updated to Nov 25, 2022)?

The current situation shows a continued decrease in the incidence of the covid-19 marker at the Prague WWTP, Kladno (Vrapice) WWTP since the second half of October, which is accompanied by a drop in the number of positively tested persons. In Brno and Břeclav, the values ​​of the covid-19 marker in wastewater are decreasing after the increase at the end of October. The latest November data show a process of stagnation (stabilization of covid-19 marker values) on all WWTP lines.

Brno WWTP – the content of virus particles in the wastewater here has reliably captured all previous waves of the epidemic. The large-scale epidemic wave that took place at the beginning of 2022 was followed in Brno by a summer wave (June-August), which, however, was not accompanied by a significantly increased incidence of clinical symptoms of covid-19, detected by PCR tests. The amount of virus particles in Brno’s wastewater is at the level of the previous wave of the epidemic in the summer months. After a decrease at the end of August, there is an increase during September and October to the highest values ​​so far. However, the ratio to the number of positive tests has been inverse since the beginning of the summer, i.e. the virus is present in the population, but does not significantly affect the population’s health status. The values ​​from the end of October show, after an initial decrease, a stagnation in the concentration of SARS-CoV-2 in wastewater in November, which, however, is not accompanied by an increased number of positively tested persons. On the contrary, it continues to decrease.

Břeclav WWTP – the waste water from this WWTP caught all the previous waves of the epidemic. The epidemic wave that took place at the beginning of 2022 and ended in May was followed by the summer epidemic wave (June-August), which is no longer accompanied by an increased incidence of clinical symptoms of covid-19, detected by PCR tests. The amount of virus particles in wastewater has been rising to its highest levels since September. However, the ratio to the number of positive tests has been inverse since the beginning of the summer, i.e. the virus is present in the population, but does not significantly affect the population’s health status. The values ​​from the end of October show, after an initial decrease, a stagnation in the concentration of SARS-CoV-2 in wastewater in November, which, however, is not accompanied by an increased number of positively tested persons. On the contrary, it continues to decrease.

Prague WWTP – on both the current and the new water line, waste water monitoring has captured the current waves of the covid-19 epidemic very well. In 2022, the wastewater from both ÚČOV lines caught an epidemic wave at the turn of January and February with a gradual decline, ending in May. In June, an increase in the covid marker was recorded on both lines, but this was not captured by clinical tests. In the summer months, there was again an increase in the amount of viral RNA in wastewater, which is no longer accompanied by the occurrence of a significant number of clinical cases. The increase in the amount of the covid marker in Prague wastewater at the beginning of October is followed by a decrease in November, which is accompanied by a decrease in the number of people tested positive.

Kladno WWTP – wastewater monitoring here captured all waves of the epidemic very well. Similarly to the Prague WWTP, in 2022, wastewater caught an epidemic wave at the turn of January and February, with a gradual decline until the beginning of May. Here, too, a rise in the covid-19 marker was detected in June, which was not detected by clinical tests. In the summer months, the amount of viral RNA in wastewater increased again to the level of previous epidemic waves, but there is no longer an increased number of clinical cases. The increase in the amount of the covid marker in Kladno wastewater at the end of September is followed by a decrease in October and November, which is accompanied by a decrease in the number of positively tested persons.

The results of wastewater monitoring in the above graphs are compared with the verified numbers of positively tested persons, from the ISIN system, continuously processed by the Department of Biostatistics of the SZÚ for specific monitored locations. Data on weekly numbers of positively tested individuals in the Czech Republic are obtained from the publicly accessible website of the European Center for Disease Prevention and Control. For the possibility of comparing current wastewater monitoring results (approx. for the last 1–2 months), freely available data from covid maps or publicly accessible websites for individual cities on the platform https://obce.nery.cz/ (in Czech) are used. Public data may contain errors and do not contain the number of inhabitants in the connected municipalities.

Fluctuations in the capture of RNA sought in wastewater can be caused by:

  • different amount of wastewater = different dilution of the amount of viral RNA fragments present,
  • by taking in another weekly regime (weekend),
  • inhomogeneity of the collected sample (waste water contains a number of other substances and particles, sampling is performed after mechanical removal of coarse impurities),
  • the volatile ratio of industrial and municipal wastewater.

You can learn more about the issue of coronavirus in surface and wastewater, and the possibilities of using the results as a diagnostic medium, in the articles of the VTEI journal here (in Czech) and here (in Czech). A Czech television (in Czech) report from Kateřina Sovová and an article in MF Dnes (in Czech) public journal from Hana Zvěřinová Mlejnková also deal with the topic.

Learn more about the ongoing project here.