Coronavirus in waste water deemed high-risk

The presence of coronavirus in waste water may increase the risk of infections.

At the end of August, coronavirus was detected in the waste water of five localities where there had been no findings by the beginning of the month, said the National Institute for Health and Welfare (THL) in a press release on Tuesday.

The monitoring that took place between 23 and 24 August and 30 and 31 August detected the presence of coronavirus at waste water treatment plants in Jyväskylä, Hämeenlinna, Kuopio, Lappeenranta, and Kouvola.

Coronavirus testing, however, detected no COVID-19 infections in the Kouvola area during the five-week period preceding the sampling (24 August).

“The presence of the virus in waste water but the absence of any detected infections is a warning sign. The area may contain unidentified infected people and the virus may be spreading in the population of the area. In this case, it may be necessary for the authorities to introduce more stringent measures against the epidemic, for example by encouraging residents to get tested for COVID-19 if they experience even minor symptoms,” said THL Senior Researcher Tarja Pitkänen.

In other areas, especially in Jyväskylä and Hämeenlinna, there have been cases of COVID-19 diagnosed since the end of July. In Kuopio and Lappeenranta, individual cases of COVID-19 have been diagnosed only in August since last spring.

In the latest extensive collection of waste water samples, on 23–24 August, coronavirus was detected in waste water in eight different hospital districts.

Samples were collected from 23 other waste water treatment plants, in addition to the five weekly monitoring sites.

“Coronavirus had been detected in individual testing around Finland, but the number of cases has not increased nationally in recent weeks. Waste water monitoring also shows that there are cases of COVID-19 occurring in several areas,” said Pitkänen.

If sampling is intensified more in some monitoring sites, the test sensitivity may differ regionally

On the other hand, there may be differences in the sensitivity of the method between different waste water networks, for example, due to the temperature of the waste water or the extent to which the waste water contains components that interfere with the enzymes used in the PCR test.

For example, in the weekly monitoring in Oulu, the genome of coronavirus has not been detected so far, even though several cases of COVID-19 have been diagnosed in the area under the Northern Ostrobothnia Hospital District in recent weeks.

A THL project examines the occurrence of coronavirus in waste water through the means of analysing untreated waste water coming to sewage treatment plants for the RNA, or genome, of coronavirus.

Launched in mid-April, the sample collection is planned to continue until the end of 2020.