COVID-19 in Wastewater

What is wastewater epidemiology?

Wastewater epidemiology is a relatively new field of research that studies the chemical and biological contents of human waste for clues about disease status and transmission, drug use, or even the overall health status for a population. It relies on the fact that all people excrete waste and that the majority of our waste is flushed away to wastewater treatment plants or septic systems.

By analyzing the wastewater at the facilities, we may be able to detect information about the resident population as a whole—that may otherwise be unknown—to enable earlier or better public health action.

What can wastewater epidemiology tell us? 

By analyzing wastewater we can test for the presence of chemicals or biological byproducts that signal whether concentrations of potential infectious diseases, like COVID-19, or other public health concerns such as the use of illicitly-acquired drugs (like fentanyl), are increasing or decreasing.

To be clear, the testing cannot identify affected individuals. Instead, it lets public health know that a concerning chemical or biological byproduct is present and to start action, such as informing the public or increasing testing (e.g., testing for COVID-19).

What do normalized viral copies and PMMoV mean?

The concentration of SARS-CoV-2 RNA in wastewater samples depends on several factors including:

• human factors - The number of people who contribute stool to the system and how much virus is shed by each person
• physical factors - Heavy rainfall and spring run off due to ice melting can dilute the sample and lower the measured concentration.

To account for these factors, the concentration of SARS-CoV-2 RNA is reported as compared to something we know is always present in human stool: pepper mild mottle virus (PMMoV). PMMoV is a plant virus that occurs in most pepper species and has very stable concentrations in human stool. The “normalized viral copies” are the concentrations of SARS-CoV-2 RNA compared to PMMoV, which give us a better estimate of the true concentration of COVID-19 virus in stool.

Why are we measuring COVID-19 in wastewater?

In the KFL&A region, we track the number of daily new cases of COVID-19, the number of active cases, and the outbreaks of COVID-19 in workplaces, schools, and specialized care facilities like retirement homes (note that testing restrictions may lead to underestimates of new cases, active cases, and outbreaks). Part of the challenges of living with COVID-19 in our communities is the fact that people may be infected with the virus (called SARS-CoV-2) but do not experience symptoms, and, unknowingly, may spread the virus more widely.

We are unable to precisely estimate the number of people who may have COVID-19, or who do not get tested, either because they do not have symptoms, are not eligible for testing, or choose not to. We do know that people with COVID-19 shed the virus in their stool whether they are symptomatic or not, and even before they are symptomatic. The water we flush or send down the drain ends up at our wastewater treatment plants.

Measuring COVID-19 in wastewater is one method that helps us estimate if the number of cases for residents are increasing or decreasing according to trends in virus counts in our wastewater. Knowing this can allow public health to respond accordingly, whether increasing public messaging and protective policies, or by relaxing restrictions when all measures of surveillance indicate that the risk of transmissions is lower.

What is SARS-CoV-2 RNA? 

How does this work in the KFL&A region?

Supported by Ontario’s Ministry of Environment, MECP), researchers at Queen’s University’s Beaty Water Research Centre (BWRC) have partnered with Utilities Kingston and Loyalist Township to measure the amount of SARS-CoV-2 RNA in samples from both of Kingston’s wastewater treatment facilities (Cataraqui Bay and Ravensview) and from Amherstview WPCP that serves the communities of Amherstview and Odessa.

Several days a week, a sample is collected from each wastewater treatment facility and transported to the BWRC lab where it is prepared and analyzed for SARS-CoV-2. Those measurements are shared with both the MECP and KFL&A Public Health, who use the results in their assessment of COVID-19 transmission risk for these communities, in addition to traditional surveillance measures.

What do our results mean? 

What are “counts per ml”? 

The “counts per ml” are the number of copies of the target RNA found in a milliliter (ml) of raw sewage from the whole community served by the specific wastewater treatment facility. We are primarily concerned with the trends in the data (for example, are the counts increasing, stable, or decreasing?) to help us interpret what is happening in the community.

When will my community’s wastewater be tested?