The secrets hidden in sewage
“Sewage surveillance is becoming more valuable right now as conventional testing is becoming less transparent. More people have been using rapid at-home tests and might not report results to a public health agency. That means the number of positive cases being reported by official sources might not actually provide a full picture of what’s happening with the pandemic.
But no matter how or if they’re testing, infected people — whether they have symptoms or not — flush out the virus when they go to the bathroom, leaving viral RNA that can be detected in wastewater samples. It requires careful collection and testing, but sewage can provide a less biased look at the viral trends in a given community.
Science has not yet reached the point where we can say that X amount of viral load in a community’s sewage means Y number of people are infected in that community. But still, knowing which way viral loads are trending is useful. If they are going up, even before the number of positive tests starts increasing, it could in theory allow public health authorities and the local health system to start preparing for a surge. If they are going down, public health officials (and the general public) can be confident that any waning in official case numbers is real and not the byproduct of, say, less testing.”
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“Surveillance programs could watch for other pathogens, too, such as influenza, hepatitis, and norovirus for early warnings of emerging outbreaks. Julianne Nassif, an expert on wastewater surveillance with the Association of Public Health Labs, said we could also monitor for bacteria, viruses, and other microbes that are resistant to current treatments. Public health officials could try to get ahead of an outbreak of antibiotic-resistant bacteria in a nursing home, for example, with the information gleaned from downstream sewage.
Johnson envisioned communities monitoring for narcotics, to better tailor their public health campaigns. Wastewater could be tested to determine whether cocaine or opioid use is rising in a given sewage shed. It could even determine what kind of opioids are being used, which could be helpful to health departments. Widespread heroin use might require a different intervention than diverted prescription opioids or black-market fentanyl.
The possibilities sound almost endless, extending to research that could help us better understand human health. Dennehy described to me one hypothetical experiment that could be run with sewage monitoring, looking for the viral markers associated with colon cancer. By comparing the results from one community with, say, a nearby nuclear power plant and another community somewhere else, we could get a better understanding of how the surrounding environment affects people’s health.
But for all of this potential to be realized, these efforts would require sustained support. The CDC bet on the wastewater boom, launching a national Covid-19 surveillance system in the fall of 2020. But dedicated investments in infrastructure and a workforce would be necessary if the country were to begin conducting wastewater surveillance on a more permanent basis.
In general, the US has not appeared willing to make big investments in public health. Scientists working on these programs hope that the same may not be true of wastewater surveillance, given the opportunities it presents.
“We learned a lot of hard-won lessons with the Covid pandemic. We got caught with our pants down at the beginning. A lot of things that we did were too late,” Dennehy told me. “The hope is we can remember these lessons for the next time this comes around, which may not be that long.””