Skip to content

Wastewater Testing Explained

Data and alert level definitions uncovered

On October 1, 2021, McGill initiated the wastewater testing project and began collecting and testing samples from the university’s downtown and Macdonald residences. The project entails testing wastewater samples taken daily from each site for the presence of COVID-19. Testing building wastewater enables researchers to detect the presence of the virus in a building’s sewage system and potentially monitor sick individuals. “While this testing cannot measure the precise amount of infection, it does provide a positive or negative result for the presence of the virus in the waste,” wrote the university in a message to the Daily. Essentially, a positive result indicates that one or more of the individuals in the building who have used the facilities are infected with COVID-19. 

The wastewater testing page is updated on a “rolling basis” with current alert levels – high, medium, or low – for each residence based on the results of the sample testing. While the page provides protocol for each alert level, it does not provide definitions for what constitutes a positive result, information on how samples are collected, or historical data from when the initiative was started. 

Given these gaps, the Daily filed an Access to Documents Request earlier this semester to gain access to data and definitions created by researchers. Here’s what we found. 

Testing Procedures

One sample is collected daily from La Citadelle, Carrefour Sherbrooke, New Residence Hall (NRH), Solin Hall, Royal Victoria College (RVC), Upper Residence, and Laird Hall. To collect the samples, researchers use a “torpedo,” a device developed in early 2021 specifically for testing the presence of COVID-19 in wastewater. They are constructed with cotton buds, medical gauze swabs, and electronegative membranes encased in narrow 3D-printed shells. The device is a “passive sampler,” meaning it can be left in a waterbody for set amount of time during which pollutants in the water will interact with the device. At McGill, torpedoes are placed in wastewater (either in a building’s outdoor man-hole or indoor washout, depending on the site), and after 24 hours, they are removed and then transported to a McGill lab in the McConnell Engineering building to be analyzed. 

The lab protocol – “SARS-CoV-2 detection by absorption” – was developed by Dominic Frigon of McGill’s Civil Engineering department and Sarah Dorner of Polytechnique Montreal’s Civil, Geological, and Mining Engineering department. First, analysts obtain a concentration of the sample; Bovine Respiratory Syntactical virus (BRSV) and Pepper Mild Mottle virus (PMMV) are also added to the sample at this stage as external controls. Next, ribonucleic acid (RNA) is extracted from the sample’s concentration. Then, a molecular detection sample PCR test is performed on the RNA extraction using a testing kit, yielding a negative or positive result. There are notes throughout the lab protocol giving guidelines for analysts; for example, the protocol notes that precision is important while obtaining the concentration, as “a precise external control is needed for data processing.” 

Indeed, data shows that results are often inconclusive. Under the “PCR notes” column, analysts were instructed to “record any departures from typical analyses and observations.” Oftentimes, inconclusive results were the result of low PMMV and/or BRSV in the sample. On other occasions, inconclusive results were the result of a lost torpedo, cross-contamination with the SARS-CoV-2 positive control, or a blocked pipe that prevented the sample from being collected, among other causes. Under the PCR notes, when there was a positive result, analysts occasionally noted whether the signal was “light,” “moderate,” or “strong.” 

Alert Level Definitions

The university outlines three different alert levels: low/vigilance level, medium/precursor level, and high/outbreak level. Low/vigilance level is the “normal” alert level, with the usual COVID-19 safety protocols in place. Medium/precursor level is reached in a building following two days of consecutive positive results. At this level, a message is sent to all residents and staff of the building advising them to wear masks, reduce their contacts, get tested, and report any positive results to Case Management. The alert returns to low/vigilant following four consecutive days of negative results. The high/outbreak alert level is reached when two or more residents report testing positive; thus, transition to this alert level is not directly through wastewater testing but is instead through Case Management. McGill’s guidelines indicate that “the alert level to which the building transitions will depend on current wastewater testing results.” 

These definitions and guidelines indicate that if a singular positive result is found, residents and staff of the building are not notified, and there is no update made to the wastewater testing website. The data collected revealed that this happened several times over the course of the semester; a positive result was found on one day, and no one in the corresponding residence was notified, nor was the website updated.

The guidelines also don’t take into account the prevalence of inconclusive results. For example, in a situation where a positive result is followed by an inconclusive result the next day, the alert level will not be changed. Testing between January 26 and January 28 at NRH yielded positive-inconclusive-positive results; however, the alert level was not raised because there were not two consecutive days of positive results. Email correspondence and meeting minutes obtained by the Daily show that research directors and those in the Emergency Operations Centre (EOC) were considering adjusting the definition for the medium/precursor level to account for a situation such as this in early February, but the project’s page does not reflect that the definition was redefined, and inconclusive results remain unexplained. 

Alert levels sent to those in residence alert them of protocols to follow when the alert level is raised, but these do not offer insight into the state of the outbreak. Uncovered email correspondence between Case Management and Student Housing and Hospitality Services revealed that there was a confirmed positive case in NRH on November 23 following two days of consecutive positive test results. However, the email sent to residents on November 23 notifying residents that the alert level was raised did not disclose the positive case in the building. 

COVID-19 in Residences

A current resident of NRH told the Daily that as of December 2, residents are no longer receiving emails about alert levels and protocols. Now, this information is only posted on the university’s website. “To my knowledge, the alert levels haven’t led to any actual changes in measures,” the resident wrote: “if anything, the measures have become more relaxed.” The past few weeks have seen an outbreak of COVID-19 at McGill, with a staggering 473 cases most recently reported on campus. On March 23, students in residences were alerted that there were no more isolation rooms available and that those who tested positive would have to isolate in their own rooms. 

When recently reporting her positive case, the aforementioned resident of NRH was instructed by case management to book a hotel room or double-mask around her roommate, who had tested negative for COVID-19. “Not the smartest since masks don’t work indefinitely, and we sleep about five feet from each other,” she commented.