Finnish health authorities have found coronavirus remains in wastewater in the cities of Helsinki and Turku.
The finding is the result of a study carried out by the National Institute for Health an Welfare (THL, in its Finnish acronym) in some of Finland's major cities.
Unlike what happened in Helsinki and Turku, the health agency emphasized that there are "no indications of the virus" in samples collected in Tampere, Kuopio and Oulu.
In April and May, THL’s water microbiology laboratory in Kuopio introduced a testing method which can be used to detect the quantity of coronavirus RNA, or its genetic material, in samples collected from sewage treatment plants. The first findings of the study have now been released.
The findings are based on composite samples taken within 24 hours on 24 and 25 May. In particular, coronavirus RNA was found in the sample collected in Viikinmäki in Helsinki.
A small quantity of viral RNA was also detected in the incoming wastewater at Kakolanmäki treatment plant in Turku. On the other hand, no indications of the coronavirus were found in samples collected at the treatment plants of Viinikanlahti in Tampere, Lehtoniemi in Kuopio and Taskila in Oulu.
The wastewater study is expected to generate more information about the scope and spread of the coronavirus outbreak. THL says the present results "indicate that this monitoring technique can be used to support preparedness for a potential second wave of the outbreak."
"Confirmed infections indicate an abating epidemic situation, and wastewater studies support the observations based on testing individuals. Wastewater testing can give us an advance warning if increasing quantities of the virus start circulating in the population again,” says Tarja Pitkänen, Senior Researcher at THL.
Samples collected at 28 plants
The collection of samples began in April at a total of 28 sewage treatment plants. For the time being, samples are collected weekly at treatment plants in Helsinki, Turku, Tampere, Kuopio and Oulu.
In addition, samples will be collected on a monthly basis in Espoo, Maarianhamina, Kotka, Kouvola, Lahti, Hämeenlinna, Lappeenranta, Pori, Mikkeli, Savonlinna, Jyväskylä, Joensuu, Seinäjoki, Vaasa, Kokkola, Kajaani, Kemi, Rovaniemi, Salo, Rauma, Pietarsaari and Vihti.
"The sample collection is currently funded by a start-up grant from the Ministry of Agriculture and Forestry, and we will focus on samples of water coming to the sewage treatment plants. At some plants, samples of wastewater sludges and water leaving the plant will also be collected in cooperation with the University of Tampere,” explains Pitkänen.
The next step will be investigating the possibilities of reliably determining the quantity of coronavirus in samples stored earlier in April and May. The results of these tests are likely to be ready in August.
"We also need to know if the coronavirus can remain viable in the water coming to sewage treatment plants," says Pitkänen.
International comparisons
The method used by THL and the results obtained are consistent with findings reported by various research groups studying wastewater around the world.
"The unique feature of the wastewater samples collected in Finland is that they cover as much as 60% of the population," explains Pitkänen.
The data produced in Finland also contribute to a European research project, the first joint measurement of which was carried out between 31 May and 1 June.
