Wastewater-based epidemiology (WBE) has been shown to be an excellent means of understanding the spread of SARS-CoV-2 in communities. It is now used in multiple areas across the world to track the prevalence of the virus, serving as a proxy for determining the status of COVID-19. Of particular importance is that WBE can be used to estimate the prevalence of COVID-19, including asymptomatic cases. However, one of the major drawbacks of WBE for SARS-CoV-2 has been that the traditional method was not very sensitive, and low viral loads could not be reliably detected.
A team of scientists from Hokkaido University and Shionogi & Co, Ltd., have developed a simple, rapid, highly sensitive method for the detection of SARS-CoV-2 in wastewater. The method, EPISENS-S, which does not require specialised equipment, was described in the journal Science of the Total Environment.
During the COVID-19 pandemic, Japan has had the lowest number of cases per capita. Thus, the viral loads in sewage have also been lower, and much more difficult to evaluate using established WBE methods — due to their low sensitivity. Prior work by the research team showed that the SARS-CoV-2 virus was associated with solids in sewage, so they focused on developing a method to analyse the solid phase of wastewater.
The method they developed, EPISENS-S, involves centrifuging collected wastewater samples to separate all the solids in the samples. The solids were then treated with a commercially available kit to extract all the 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 that is currently widely implemented in Japan. The DNA obtained from each of these methods was subjected to quantitative PCR (qPCR).
The team found that the EPISENS-S method is approximately 100 times more sensitive than the polyethylene glycol method. They used EPISENS-S to conduct a long-term analysis of wastewater from two sewage treatment plants in Sapporo city, and found that there was a high correlation between changes in RNA concentrations in the collected samples and changes in the number of reported cases in the city. EPISENS-S can also detect and quantify the Pepper mild mottle virus (PMMoV), which is associated with fecal matter and is used as an internal control.
EPISENS-S provides a way to track COVID-19 cases that are asymptomatic, as well as those that have not been clinically confirmed. In addition, 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 track other viral diseases with low infection numbers and viral loads.
Materials provided by Hokkaido University. Note: Content may be edited for style and length.