#FEMSmicroBlog: From drain to data – tackling local COVID-19 outbreaks with wastewater testing
Wastewater testing has become crucial to predict COVID-19 outbreaks in local communities. Especially in social surroundings like a University campus, wastewater surveillance can inform health authorities to prevent the further spread of SARS-CoV-2. The study “Efficacy of SARS-CoV-2 wastewater surveillance for detection of COVID-19 at a residential private college” published in FEMS Microbes analyses surveillance testing on a small campus. In this #BehindThePaper interview, Geoffrey Holm explains the limitations of this approach, and how it helps unfold the dynamics of community infections. #FEMSmicroBlog
Why did wastewater surveillance become such an important tool to tackle the COVID-19 pandemic?
Wastewater surveillance, at least at a municipal level, can be an extremely important tool as an early indicator of community spread. First, there is a huge delay between when an individual becomes infected and when they seek medical attention.
Second, since SARS-CoV-2 can spread asymptomatically, often the virus can be circulating in a community for a week or two before it comes to the attention of medical personnel due to doctor’s visits or hospitalizations.
This is especially true when only a little individual surveillance testing occurs in a community. So, most of the positive tests are from symptomatic individuals seeking medical care. In these situations, you can start to detect increases in SARS-CoV-2 RNA levels in the waste stream well prior to a surge in cases.
A great illustration of this is the wastewater surveillance levels in the greater Boston area ahead of the recent omicron surge. Ideally, you could use this information to understand when to employ other non-pharmaceutical interventions, such as masking, in a community.
Why did you choose to analyse wastewater samples on a campus?
When we were planning the 2020-2021 academic year, starting in May 2020, individual surveillance testing capacity was limited. Plus, we were worried that we would not be able to test for the presence of SARS-CoV-2 in our student population at a level that would allow us to control the virus spread.
So, we talked with colleagues at other local institutions, particularly Syracuse University and SUNY-ESF. They were developing wastewater surveillance protocols and suggested that we could establish a similar system at Colgate.
Since I was unable to use my laboratory to conduct my own research – due to the COVID-19-related restrictions – I instead decided to turn my laboratory into a wastewater testing center. We hoped to use wastewater testing to identify particular dormitories that may have positive individuals. The idea was then to follow up with individual testing to identify positive cases.
What can we learn from your research about the shedding of viral RNA?
Through our sampling, we were able to detect SARS-CoV-2 RNA in the waste stream of dormitories from which we subsequently detected positive cases. However, we often found that the wastewater signal would increase right after students returned to the dorm following their isolation period. So, we wouldn’t necessarily detect new positive cases in that dorm.
This could be because our individual testing may have missed some positive cases. Another possibility is that other individuals not living in those dorms (such as custodians or other visitors) were contributing to the waste stream.
Alternatively, it could be an indication that those individuals returning to the dorms continued to shed SARS-CoV-2 RNA into the waste stream for a substantial time period after the infection. Given other reports in the literature, we favor this latter possibility.
In the end, it means that it was difficult to differentiate between new positive cases and “old” cases, which limits the utility of wastewater testing. Also, the small watershed that was sampled at each location and that contained the wastewater from 1-3 dorms suggested the waste stream be highly variable.
Flow rates vary tremendously, and it was challenging to get a consistent sample. Sample collection at a much larger facility, such as a municipal wastewater plant, or even a sewage lift station, can provide much more reliable sampling. This would better indicate the dynamics of community infection.
- Read the paper “Efficacy of SARS-CoV-2 wastewater surveillance for detection of COVID-19 at a residential private college” by Landstrom et al. (2022) in FEMS Microbe.
- Read more on the #FEMSmicroBlog: Wastewater samples to predict viral outbreaks.
#BehindThePaper posts on the #FEMSmicroBlog aim to bring the science closer to different audiences and to tell more about the scientific or personal journey to come to the results.
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