SARS-CoV-2 Detection in Wastewater using Droplet Digital PCR by Tami Sivy, Ph.D.

Before the COVID-19 pandemic, what was your primary role or field of research?

Before the pandemic, my primary research focus was in beach testing for fecal contamination with qPCR and microbial source tracking of fecal contamination using ddPCR. I am also the primary advisor of all SVSU’s biochemistry majors and am constantly looking for new ways to improve classic teaching methods to give my students the best learning experience possible.

How severely has your region been impacted by the pandemic?

Fortunately, our rates have not been not very high compared to other more densely packed areas of Michigan.

How did this wastewater project come about? Who seeded the idea and when?

In late March, Shannon Briggs from the Michigan Department of Environment, Great Lakes, and Energy approached our group at Saginaw Valley State University about using our ddPCR instrumentation to start monitoring wastewater from regional wastewater treatment plants.

What was the primary goal? What did you hope to determine or achieve?

In the short term, our goal is to establish the baseline SARS-CoV-2 levels from each community that we’re monitoring so that we’ll be able to recognize if there is a spike in infection rate. In the long-term, we hope to be able to translate our wastewater monitoring results into a method that can be used to track virus levels for any given community.

Why did you choose to use ddPCR technology to measure SARS-CoV-2? What Bio-Rad ddPCR platforms did you use to perform your research?

We use the QX200 Droplet Digital PCR System to conduct our research. We’ve been using it for our microbials source tracking work and the sensitivity with this instrument is just outstanding. We were also worried that there might be chemicals that could inhibit RT-PCR in wastewater samples, so using ddPCR was a natural choice because it is not as susceptible. Last but not least, because ddPCR provides a direct count of our target DNA — rather than the relative measurement that you get from RT-PCR — we don’t have to run standard curves regularly.

What was the scope of the project — for example, how many people were in the wastewater catchment area?

Our monitoring encompasses the Great Lakes Bay Region and the Thumb, here in Michigan. We are testing 14 different wastewater treatment plants as well as the university, which all together represent nearly 1 million people.

What were the key outcomes/findings from your project?

Our project is ongoing and we’re learning more about wastewater testing every day, so we’d like to gather more data before drawing any major conclusions from our work. One thing we have established however is our methods: The sampling and ddPCR-based testing protocols are working great and we’re confident in the quality of data we’re collecting.

How do you think wastewater testing using ddPCR might help stop the spread of SARS-CoV-2 in different communities?

It appears that viral RNA can be detected in waste up to one week before a person displays symptoms of the infection. This means that wastewater can act as a kind of early warning system that detects infection while a person is still presymptomatic, before they realize that they need to be tested for COVID-19. Furthermore, it can indicate true infection rates for a community, as it can pick up on genetic material excreted by a significant number of asymptomatic individuals — up to 40% of those infected with SARS-Cov-2. Both presymptomatic asymptomatic individuals are capable of infecting others, so using wastewater to identify them can support measures such as self-isolation or proactive testing to help stop the spread of COVID-19 within a community.