This indirect monitoring technique of the virus makes it possible to spot its spread among the population at an early stage.

The first results of the CORONASTEP study were published on Wednesday, 18 May. The goal of the study is to record the presence or the resurfacing of the virus in Luxembourg as early as possible by using wastewater samples.

The method of testing wastewater for the virus is very sensitive. This means that even small amounts of the virus can be detected in the samples. Researchers at the Luxembourg Institute of Science and Technology (LIST) were for instance able to prove that SARS-CoV-2 was already present in Luxembourg at the end of February.

This monitoring method complements the CON-VINCE study in which asymptomatic people are systematically being tested, also in order to get an understanding of the spread among the population. It is an additional tool to trace the consequences of the lifting of the lockdown restrictions.
The CORONASTEP study is conducted by Dr Leslie Ogorzaly and Dr Henry-Michel Cauchie at LIST.

A real-time recording of the infestation status of a population of 300,000 people

The technology used by LIST enables the researchers to determine the general infestation status among a population of over 300,000 people (i.e. the number of people connected to the monitored treatment plants) in just one day.

This global picture of the level of contamination is no substitute for the analysis of human samples, but it completes them. The technology will help to discover a possible new rise in the presence of Covid-19 among the population.

Covid-19 circulated in Luxembourg since 25 February 2020

Traces of the SARS-CoV-2 genomes were found in wastewater samples taken as soon as 25 February 2020, i.e. before the first human samples were tested for SARS-CoV-2 in Luxembourg.

During the first wave of infections in Luxembourg from mid-March until mid-May, the virus concentration in the wastewater closely followed the curve of officially announced positive Covid-19 cases.

The wastewater samples originate from a joint project between LIST and the National Health Laboratory (LNS) which started in April 2019.

Wastewater samples still hold secrets to be revealed

Viruses are present in wastewater in relatively low concentrations. Before the wastewater samples are analysed in LIST laboratories, they are concentrated. The concentrated samples are stored at LIST and are expected to deliver further results in the future, especially thanks to a collaboration between the Luxembourg Institute of Health (LIH), the University of Luxembourg, and LNS. The goal is to decipher the entire genome of the viruses found in the wastewater samples in order to determine if there are genetic mutations of SARS-CoV-2 circulating among the population of Luxembourg.

Other analysis techniques are also being tested to extend wastewater analysis in Luxembourg. The multidisciplinary team currently responsible for the modelling of epidemiological data in the national Covid-19 task force will also conduct a precise analysis of the relation between human cases, their geographic location, and the data obtained through wastewater. All collected scientific data is a very useful support in monitoring the decrease of the infection rate among the population during the different stages of restrictions being lifted.

A long-time activity for LIST

The LIST's group of environmental microbiology has been studying viruses in wastewater for over 10 years. In combination with data derived from human stool samples from LNS, this research has helped to get a better understanding of how noroviruses or enteroviruses spread. Noroviruses are responsible for gastrointestinal upset mainly occurring during the winter season and enteroviruses for a wide range of mild or severe symptoms (foot hand-mouth syndrome, angina, respiratory diseases, diarrhoea, heart disease, acute flaccid paralysis, or meningitis).

The CORONASTEP study was made possible thanks to the collaboration with wastewater treatment trade unions (SIDEN, SIDERO, SIDEST). Recently, a number of hospitals, e.g. the Emile Mayrisch Hospital Center (CHEM) and the Centre Hospitalier de Luxembourg (CHL), have also granted access to their sewers in order to monitor the virus as closely to infected people as possible.

The significance of setting up effective monitoring networks

The reconstruction of the virus dynamic in Luxembourgish wastewater thanks to samples taken before the start of the health crisis stresses the value of long-term wastewater monitoring programmes. On a European level LIST is a partner of the most important teams currently working on this subject. The cooperation was often already in place before the pandemic and has been intensified over the past months.

Author: LIST

Editor: Michèle Weber (FNR)