Researchers are scouring the nation’s sewers for clues about how infectious strains of the virus that causes COVID-19 ended up there and how long they can survive.
While the virus doesn’t pose a big risk to sanitation workers or the public, the research is critical for offering reassurances that operators of the nation’s drinking water and wastewater systems are taking the right precautions to protect the public, said Charles Gerba, a professor of microbiology at the University of Arizona.
"You want to make sure the wastewater treatment process is adequate for the removal of the virus and killing it, so we have that assurance," Gerba said. "It’s a new virus, and you want to remove any doubts."
"We’re working on the methods and the efficiency of detecting the virus; it’s poor right now, based on our assessment, and needs improvement," Gerba continued. "It really needs to be standardized and improved a lot. You can’t just run out and test a sewage sample with a clinical kit."
A key question the researchers are wrestling with is to what extent humans excrete infectious coronavirus into wastewater — through stool, urine, saliva or phlegm.
Kyle Bibby, an associate professor at the University of Notre Dame, said there’s limited evidence of the coronavirus in stool being infectious, though it’s certainly a possibility. "There’s some legitimate scientific uncertainty," he said.
Bibby also noted that recent studies have found high viral loads in the phlegm of infected patients — another avenue that needs to be investigated. "To me, it’s quite possible that could also enter a sewage or wastewater system. All of these would need to be better understood," he said.
The Centers for Disease Control and Prevention said in an email that the virus has been found in untreated wastewater, and researchers don’t know whether it can cause disease to someone exposed to sewage systems or untreated wastewater.
"There is no evidence to date that this has occurred. At this time, the risk of transmission of the virus that causes COVID-19 through properly designed and maintained sewerage systems is thought to be low," according to CDC.
Alexandria Boehm, a Stanford University professor of civil and environmental engineering, noted the difficulty researchers have faced in trying to reproduce the virus in feces. "Scientists have tried to culture it … and there are only a couple reports of them being able to actually get an infectious virus from feces," she said. "There are a lot of failed attempts."
Both Boehm and Bibby emphasized that the nation’s drinking water systems have sufficient protections in place. Bibby said the systems are built to handle "tougher" microorganisms and that people should not be afraid to use their tap water. "This virus isn’t especially tough," he said.
The need for data has increased pressure on agencies like EPA and CDC, which are studying viral loads in wastewater, whether it is in an infectious state and how it moves through wastewater systems.
EPA said in a statement that the two agencies are conducting research to develop and apply methods for measuring the coronavirus in wastewater before it has been treated.
"If proven valid by our research, the methods can be used to determine infectivity, persistence, and treatment efficacies related to SARS-CoV-2 in wastewater," the statement said. "Not until we have valid methods can researchers begin to accurately conduct more comprehensive studies."
Late last month, EPA Administrator Andrew Wheeler also noted that the agency was looking into detecting the virus in wastewater.
"This information will help public health agencies by acting as an early warning system and can identify if there is an outbreak in a specific community. Public health agencies can then take early action to reduce the spread of COVID-19," EPA said at the time.
Aaron Packman, a professor of civil and environmental engineering at Northwestern University who has worked on infectious waterborne diseases for 20 years, said he sees a need for more research to gauge the level of coronavirus in wastewater.
"To me, there are significant risk indicators, and we’ll only know once we start measuring in wastewater," Packman said. "We need to collect and analyze samples to determine the concentration of actual infective viruses in our water systems."
As researchers push to learn more, they acknowledge the data isn’t quite ready for prime time.
"A lot of the data is anecdotal or is in preprint, which is not how you’d traditionally write about something like this," said Bibby.
A paper Bibby co-authored and published in the journal Science of the Total Environment identifies the need to better detect and track the virus in wastewater, understand how it survives in water and wastewater, and assess the presence and concentrations of respiratory viruses like those that cause COVID-19 in wastewater.
Boehm said studies should also assess the persistence of the coronavirus in water and wastewater. Based on the behavior of other coronaviruses, she expects it will be very susceptible to disinfectants.
"I think everyone would like to see, though, that it is, and I’m sure those studies are happening now, but they’re not peer-reviewed," she said.
Sound advice: Avoid sewage-tainted water
What’s more, Boehm said, people generally know that it’s not a good idea to drink or swim in raw sewage.
"When there are [combined sewer overflows] or [sanitary sewer overflows] into swimming waters, people are not allowed to swim because we know there are pathogens in sewage," she wrote in an email. "Also, no one wants to drink sewage."
In March, health and wastewater officials in Chicago advised residents to avoid swimming, fishing or recreating in the city’s waterways until the pandemic passes to avoid contact with wastewater that may carry sewage.
While stressing that there was no clear evidence of COVID-19 transmission through wastewater, Chicago officials said, "it is well established that other pathogens that cause illness can be present in rivers, lakes and streams."
Allison Fore, spokeswoman for the Metropolitan Water Reclamation District of Greater Chicago, said the agency acted out of an abundance of caution with its public notice and that the advisory remains in place for its 5.25 million customers.
While downplaying any immediate risk, Heng Zhang, the district’s assistant director of monitoring and research, said the agency is collecting and freezing samples from sewage treatment plants to assist ongoing COVID-19 research at Stanford. It is also collaborating with the private-sector firm Stemloop and Northwestern to explore rapid detection of the virus using biosensor devices.
Citing recent collaboration with the Water Research Foundation, Zhang said, "The experts felt strongly that there is still a research gap on infectious SARS-CoV-2 in wastewater in sewersheds and wastewater treatment processes."
As in other older cities, Chicago stormwater and wastewater are often routed through the same network of pipes. During heavy rain events, sewage and stormwater can mix and then be discharged into local waterways. While the city has worked hard to reduce backups and limit stormwater outflows into the city’s rivers and Lake Michigan, it still happens on occasion, officials say.
Aiming for detection strategy by this fall
Separately from gauging just how many infectious viruses are in the nation’s wastewater, scientists are also focused on tracking the spread of the virus.
That’s because they’ve concluded that analysis of urine and stool in wastewater samples can reveal higher numbers of people infected with COVID-19 than have been clinically confirmed (Greenwire, May 6).
"It is important to determine whether what is detected in stool samples is due to infectious virus particles or to fragments of virus proteins or RNA," said John Stegeman, a senior scientist and expert in biochemical toxicology at the Woods Hole Oceanographic Institution in Massachusetts. "This is important to assessing whether there is potential for infectivity from droplets aerosolized from flushing."
It’s not a new practice. Gerba said he’s been monitoring viruses at the wastewater plant at the University of Arizona for the past seven years, and experts abroad have been using waste streams to track polio cases in countries like Afghanistan and Pakistan for decades.
Gerba said the information gleaned can reveal the prevalence of infection within the tested community as well as the evolution of a virus over time.
"Are we going to see it like influenza, like every year, or will it become more virulent or less virulent?" he said. "By sequencing the RNA, you can tell that."
The data is also useful since some virus carriers are asymptomatic and there is limited availability of clinical tests.
Researchers like Gerba, Boehm and others are hoping lessons learned from tracking RNA throughout the summer will result in a national strategy next fall.
"The hope …. [is] cases will decrease in the summer because coronaviruses are wintertime viruses, but we don’t know that for sure with this new one," he said. "The idea is things will be more in place by the fall … to see if the virus is spreading again."
A spokesperson for EPA said preliminary research indicates that monitoring wastewater for the presence of SARS-CoV-2 may be useful as a sensitive early indicator of levels of infections in the community.
"Having an early warning system to alert public health officials about infection in a community would be helpful," the spokesperson said. "Likewise, monitoring SARS-CoV-2 in wastewater may also provide an indication of decreasing levels of infection within a community."
Reporter Daniel Cusick contributed.