Wastewater-based epidemiology (WBE) has proven to be an excellent way to understand the spread of SARS-CoV-2 in communities. It is now used in several parts of the world to track the prevalence of the virus, serving as a proxy for determining the status of COVID-19. It is particularly important that WBE can be used to estimate the prevalence of COVID-19, including asymptomatic cases. However, one of the main drawbacks of WBE for SARS-CoV-2 is that the traditional method was not very sensitive and low viral loads could not be detected reliably.
A team of scientists from Hokkaido University and Shionogi & Co, Ltd., have developed a simple, rapid and highly sensitive method for the detection of SARS-CoV-2 in wastewater. The method, EPISENS-S, which does not require specialized equipment, was described in the journal Total Environmental Science.
During the COVID-19 pandemic, Japan recorded the lowest number of cases per capita. Thus, viral loads in wastewater were also lower and much more difficult to assess using established WBE methods; due to their low sensitivity. Previous work by the research team showed that the SARS-CoV-2 virus was associated with solids in wastewater, so they focused on developing a method to analyze the solid phase of wastewater.
The method they developed, EPISENS-S, involves centrifuging collected wastewater samples to separate all solids from the samples. The solids were then treated with a commercially available kit to extract all RNA; the RNA was then reverse transcribed and amplified to obtain a substantial amount of DNA copies. A separate set of samples was subjected to treatment with polyethylene glycol followed by RNA extraction and reverse transcription to synthesize DNA: the method which is currently widely implemented in Japan. DNA obtained from each of these methods was subjected to quantitative PCR (qPCR).
The team found that the EPISENS-S method is about 100 times more sensitive than the polyethylene glycol method. They used EPISENS-S to perform a long-term analysis of wastewater from two wastewater treatment plants in the city of Sapporo and found that there was a strong correlation between changes in RNA concentrations in the samples collected and changes in the number of cases reported in the city. EPISENS-S can also detect and quantify Pepper Mild Mottle Virus (PMMoV), which is associated with faeces and is used as an internal control.
EPISENS-S tracks asymptomatic COVID-19 cases, as well as those that have not been clinically confirmed. Additionally, it has great potential to continue tracking the prevalence of SARS-CoV-2 as vaccination rates increase. Finally, EPISENS-S could also be adapted to monitor other viral diseases with a low number of infections and a low viral load.
Ando, H., et al. (2022) The Efficient and Convenient Virus Identification System with Enhanced Sensitivity for Solids (EPISENS-S): A Rapid and Cost-Effective SARS-CoV-2 RNA Detection Method for Routine Water Monitoring worn out. Science of the total environment. doi.org/10.1016/j.scitotenv.2022.157101.