Sewage is helping researchers in San Diego and other places because wastewater can show whether there are a lot of COVID-19 infections in a particular region.
But does the presence of the virus in sewage pose a health risk? The answer is not completely clear.
UC San Diego has already used the waste stream to identify local COVID-19 outbreaks.
“Each dorm has its own sewage system,” said Kim Prather, an atmospheric chemist at the Scripps Institution of Oceanography at UCSD.
She is helping develop air-sampling techniques and she is paying attention to others, like sewage sampling.
“Since we can’t test everybody all the time,” Prather said. “That’s the way that we’ll do that very frequently so if (parts of the COVID-19 virus) starts to go up in the sewage of a particular dorm then we can figure out how to test and isolate the students in that dorm.”
The sewage testing has already led to two people who were coronavirus positive but not showing symptoms. The virus was found in sewage coming from several campus buildings, the infected school employees were identified and isolated, and a potential outbreak was stopped.
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“The same receptors that take it to the lung take it to the gastrointestinal tract there as well. So the virus grows in the GI tract and is shed in the stool,” said Robert Schooley, a distinguished professor of medicine at UCSD.
Researchers look for RNA, parts of the virus that persist in the waste stream. The presence of that genetic material can serve as an early warning beacon.
Scientists are not looking for active viruses capable of infecting another host and it's not clear they would find them.
“To be infectious the virus has to be present as a full viral particle surrounded by a very delicate, basically bubble of detergent,” Schooley said. “And so the kids of things that get done in sewage treatment plants are just the kinds of things this virus doesn’t like.”
But in untreated sewage, the virus could potentially survive.
In fact, high concentrations of airborne particles of the SARS COVID virus got into a Hong Kong apartment complex in 2003.
The aerosols came from a pool of sewage stored beneath the building. The airborne particles spread through the building’s plumbing and infected residents who were not wearing facemasks.
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“This was not treated sewage water,” Schooley said. “The apartment complex was called the Amoy Gardens complex. And the best evidence we have is that the virus aerosolized from this untreated sewage pool and with air currents it was able to spread through the air.”
But the virus is unlikely to survive in the local waste stream is it makes it to a water treatment plant.
“They haven’t adapted very well to survive outside of the host,” said Shauna Lorance, the city of San Diego’s Director of Public Utilities. “However some may possibly get through meaning they’re still viable or contagious.”
But she says it is unlikely an infection virus would survive all the water treatment that goes on at a plant.
“All of our processes, what we’re very sure of is that it's not just one layer. That it is multiple layers of treatment,” Lorance said. “So if for some bizarre reason something got through one, there are still additional treatment plant processes that will take care of it.”
Recycling wastewater involves even more treatment and when the city’s Pure Water project is up and running, treated wastewater will have undergone even more distinction treatments. That will produce distilled pathogen-free water.
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But not all wastewater gets treated before it enters the environment.
San Diego has endured millions of gallons of sewage-tainted cross-border flows since COVID-19 hit the region in spring.
“There is a potential public health risk for a lot of pathogens in untreated sewage water, whether it’s from the Tijuana River or the Mississippi River,” Schooley said.
Sunlight and dilution can go a long way toward reducing the risk of a virus, like COVID-19, but Schooley said treating the wastewater is the best step to protecting public safety.
