chemistry and molecular biology

Estonian researchers: wastewater reveals the actual spread of the coronavirus

Filtration ponds. Photo credit: UnspIash, Ivan Bandura
Filtration ponds. Photo credit: UnspIash, Ivan Bandura

How much has the coronavirus spread in the country? University of Tartu researchers have determined that the biological waste in the sewage gives the best overview of the situation.

Wastewater monitoring has grown into a novel research field in the last decades. It has proven to be a successful strategy to detect the chemical and biological markers released into the environment by humans and to monitor the changes. Wastewater analyses allow us to detect the traces of drugs and antibiotics, but also viruses. Therefore, it is an important tool in detecting the early signs of the spread of the coronavirus.

Wastewater monitoring as a reliable tool

The monitoring of the wastewater started in the 1990s, when researchers focused on the fight against polio. Thanks to vaccination, the spread of the virus was taken under control. But the problem with the polio virus was the fact that in many cases, the infected people did not have any symptoms. This is why some of the infected people still spread the virus even though it was believed that the virus was defeated in a specific region. Luckily, researchers soon discovered that the presence of the virus was detectable from sewage samples and started gathering information. Therefore, it was easier to protect the people in that region with the vaccine.

Similarly, in the current pandemic, there is a need for an effective method to detect the spread of the coronavirus. Unfortunately, it has been a great challenge for researchers to get a good overview of the spread of the virus. At the beginning of the pandemic, the spread was evaluated based on the number of hospitalised patients and deaths. Later, more attention was paid to the serological data; that is, the prevalence of antibodies indicating contact with the virus.

Wastewater samples analysed at the laboratories of the University of Tartu Institute of Technology. Photo credit: Margit Meiesaar

Monitoring coronavirus spread

One of the most promising methods to map the spread of the virus is to systematically measure the virus concentration in wastewater. This approach allows us to get general data in a short time and thereby estimate the true spread of the virus (including latent spread). Wastewater monitoring gives the opportunity to investigate a large proportion of population over a long period of time. According to the collected data, the system for testing of people can be adapted. In addition, it can be used to confirm the end of the virus outbreak and, more importantly, the extent of asymptomatic virus spread.

The possibility of monitoring coronavirus from the wastewater was first reported by researchers in the Netherlands. A week after the first documented case of the coronavirus in the Netherlands at the beginning of March this year, the RNA of the virus was detected from the wastewater. Soon, similar reports came from Spain, Italy, France and the USA. In addition, the monitoring stations in Pakistan, which on daily basis monitor wastewater for polio virus, also detected the spread of the coronavirus.

Coronavirus spreads with droplets that are invisible to the human eye. Infected people spread it by coughing, sneezing, talking or breathing. Relatively soon, however, researchers found that the coronavirus RNA could be detected from the faeces of the infected patients. This is due to the fact that the coronavirus can also infect inner intestine cells that have the ACE2 receptor that coronavirus uses to enter the cells. There is a different amount of RNA in the faeces of different patients and the amount depends on the course of the disease. Nevertheless, the virus can be detected even after it is gone from the patient’s respiratory tract or in asymptomatic cases.

Analysing the wastewater gives us information about the virus spread already before an outbreak in the specific region. Photo credit: Margit Meiesaar.

Wastewater warns and predicts

The latency of the virus is up to two weeks, meaning that the infected people spread the virus before having any symptoms. On the other hand, research has shown that in that time period, there are already virus particles in the faeces. Therefore, analysing the wastewater gives us information about the virus spread already before an outbreak in the specific region.

In many cases, the warning signs from wastewater analysis have come true. The connection between the coronavirus RNA detected from wastewater and the number of infected patients has been shown in the Netherlands, France and the USA. Most of the time, the results predict the spread of the infection in a region in five to seven days. A rise in the RNA concentration could also mean a rise in the number of patients that need hospitalization. And vice versa, if the RNA concentration in wastewater decreases, it indicates a decline in positive test results in near future.

The above information allows to conclude that the monitoring of wastewater is an effective strategy to monitor the spread of the virus. It allows to collect data even from regions with limited access to healthcare facilities. Wastewater monitoring has several benefits – it gives the chance to get a fast and thorough overview of virus spread in a specific population, but also in the whole country. Therefore, it is cheaper and more convenient for the people than massive testing.

Currently, wastewater is collected for coronavirus monitoring from Monday to Wednesday. The samples are analysed from Wednesday to Friday at the laboratories of the University of Tartu Institute of Technology. By Friday afternoon, the results are clear and sent to the Estonian Health Board. The monitoring is led by Professor Tanel Tenson and Senior Research Fellow Veljo Kisand.

Further information: 
Mare Vahtre

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