The latest scoop on COVID & poop

Our experts Susan and Lindsey are back!

Experts: Susan Johnson and Lindsey Shultz

Susan Johnson (PhD) is an immunologist in the private biotech sector in San Francisco with training in immunology and infectious diseases from the Walter and Eliza Hall Institute and the WHO collaborative centre for neonatal vaccinology at University of Geneva. Lindsey Shultz (MD/MPH) is a physician and public health analyst interested in harms reduction, health policy, & science communication.

Below, read a conversation from our COVID Explained Slack workspace between some of our experts about the potential to use wastewater to anticipate and contain outbreaks.

You may recall from our explainer on COVID-19 poop detection (newly updated!) that people who have COVID-19 shed the SARS-CoV-2 virus in their feces. And since viral replication and shedding typically begins before people feel sick (and certainly before they end up in the hospital), it is possible to detect the virus in the poop of infected individuals before symptoms show and patients seek care. Recently, researchers have investigated whether we can use wastewater to detect COVID outbreaks.

A research team at Yale believes that this method is giving them a better idea of viral spread in the New Haven. Each week, they report virus levels detected in sewage samples to the New Haven city officials. As New Haven starts to reopen, they expect to detect elevated levels of virus in the sewage, and this information will give the city an opportunity to act quicker than if they were depending on hospital data. 

Carmel, Indiana has partnered with biotech company Biobot to collect and analyze the levels of virus in their wastewater. Mayor Jim Bainard says that if the sewage data shows a spike, he knows that they’ll need to draw back on some of their reopening.

Though this has been pioneered at the University of Arizona, several other universities, including Syracuse and University of California San Diego, are also implementing sewage testing in an attempt to detect and halt potential outbreaks on campus.

Fecal sampling is unlikely to be our major viral detection tool: testing is still super important to identify infection on an individual level. However, as an addition to the slate of possible detection methods, it’s proven useful so far. Relative to doing medical testing on all individuals in the population, collecting poop from a vat is much, much easier.  

Our experts discuss this article, which highlights how researchers at the University of Arizona were able to trace and prevent a COVID-19 outbreak using a method of wastewater-based epidemiology. 

Susan: It’s an interesting strategy but I don’t know how it works for big places, surely the water would have to be sequestered somehow. I have no idea how sewage systems work but you would have to somehow get samples from small groups.

Lindsey: Yeah I buy that it's a real effect — and maybe prevented a cluster here — that's great! But it didn't look like the University of Arizona had a strong policy in place about testing students beyond their initial arrival back to campus. I think this wastewater testing is a good complement (someone referred to it as pooled poop testing) to an overall monitoring plan.

Susan: I don’t think you can use this in place of testing. It would be an interesting strategy for maintenance: continually test when areas have low case rates.

Lindsey: Yeah, the obvious comparison is waste-water monitoring for evidence of polio. A disease you expect a prevalence of basically zero, where you wouldn't necessarily need super precise, quick turn around of where the water with evidence of infection was coming from.

Susan: Exactly. It’s also an interesting thing to study for vaccines. Viral shedding can increase herd immunity, it’s why the live polio vaccine was so effective — babies shed virus for 60 days. I think they have switched to the inactive one now, though it depends on the country.

Lindsey: Yep, I think I even remember reading about a waste-water study following the switch from oral to injectable where you can see the big shedding decline.

Susan: But I don’t know how relevant this would be unless you could have a really good way to isolate the sewage systems? Maybe campuses have that? Or large apartment buildings? Office buildings?

Susan: My knowledge of sewer systems is not great...

Lindsey: I think the Yale studies were looking at New Haven in general as proof of concept — and sure you can see a reasonably good signal that precedes the outbreak curves. 

What I'm not sure about is if those signals gave any more lead time than everything else we're monitoring. For example, assume we're at a place where we have an OPV-like vaccine, the transmission is low most places, is it a cheap signal that might be useful for monitoring then? Sure. I'm just not sure what it adds when we're still at what 40k cases a day, with active monitoring. This is not to discourage studying & validating it, just not making it the backbone of a strategy yet.

Emily: I agree. I think you need a very specific setup and also low prevalence.

Susan: Yeah I think finding new complicated ways to measure seems pointless. We need to make testing more widespread and efficient. It would be great in places with low prevalence

Lindsey: Yeah I think this might be great for addressing a future problem—and I am fully supportive of mid- to long-term thinking.

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