Coronavirus stays preserved in frozen wastewater

The storage life of coronavirus RNA, i.e., its genome, in wastewater was assessed in a study of the National Institute for Health and Welfare (THL) which examined samples kept at different temperatures.

The prevalence of the virus in wastewater samples was measured based on the number of RNA copies, said a THL press release on Tuesday.

The genome was best preserved in wastewater samples kept for three months in a freezer (-20°C) and in deep freeze (-75°C). In samples kept in a cold room (4°C) the number of copies of the genome declined in the first month of monitoring.

Coronavirus genome material was first detected in Finland in a bulk sample taken at the Viikinmäki sewage treatment plant in Helsinki on 19-20 April.

The storage life of the genome was studied using partial samples taken from that wastewater sample at different temperatures one, two, and three months after the sample was taken.

“Understanding the storage qualities of the genome under different conditions is important. If the samples cannot be analysed immediately, the study suggests that it is best to freeze them. This way, the numbers of gene copies will remain stable for months”, said THL leading specialist Tarja Pitkänen.

The study also showed that particles and solid materials contained in the stored wastewater, in addition to the actual wastewater, can also improve the sensitivity of the coronavirus.