Local governments in the US are also turning to the tests, which detect traces of coronavirus genetic material -- known as RNA -- in fecal matter.
The data can be used to gain a sense of how many people may have had the virus asymptomatically and are passing it through, in addition to those testing positive because they are outwardly sick, New Castle County Executive Matt Meyer told CNN.
His county in Delaware has partnered with Biobot -- an MIT-based startup -- to screen wastewater for coronavirus. Biobot is testing sewage in 150 facilities across 30 states, according to a company spokeswoman.
New Castle County just completed its first week of testing and expects to have results early this week, Meyer said. In its pilot 24-hour test, Biobot estimated there were 15,200 cases of Covid-19 in New Castle County alone. Those results would far outpace the 4,034 estimated number of confirmed cases in the state, according to Johns Hopkins University data.
"We're confident as we do this weekly, now that we're working with Biobot, that this can give a varying indication of the total number of cases in our county, which is somewhat useful," Meyer said. "We want to identify hotspots, run this at 10 treatment facilities across a county of 560,000 people, and find out with these hotspots where they are and where they're not."
Meyer said he has spoken with state officials about implementing wastewater testing across the state -- though he said he's been met with some skepticism.
"I think it's fair there's skepticism, to be honest," Meyer said. "What (Biobot is) doing seems really smart. The science seems sound. There are uncertainties everywhere ... I hope this works and we've got to be skeptical."
'Early warning system'
Meanwhile, in the Syracuse area of New York, four professors across three universities have partnered up to test Onondaga County wastewater using a centrifugal process to isolate the virus -- a process they say could significantly speed up detection of Covid-19 outbreaks.
David Larsen, a public health professor at Syracuse University, told CNN he organized the project after coming across a paper showing that scientists in the Netherlands had successfully performed a wastewater test for Covid-19.
Larsen said he recruited his colleague Teng Zeng in Syracuse's engineering department to collaborate with wastewater facilities in Onondaga County. Samples were then sent to Hyatt Green and Frank Middleton, both of whom are part of the State University of New York (SUNY) system
Middleton, a professor at SUNY Upstate Medical University, said the isolation process they have devised adheres RNA samples of Covid-19 in wastewater to polyethylene glycol, a resin that destroys the active virus and concentrates into a pellet.
The pellet is then tested through a process known as polymerase chain reaction (PCR). The PCR is used to detect Covid-19 specifically, as opposed to other viruses that may have found their way into the testing samples, Middleton said.
He estimated that in the group's academic lab, they could test up to 100 samples a day, though if there were enough samples provided, PCR could perform as many as 1,500 tests daily.
"This is unlike anything that I've done in the past," Middleton, who serves as the director of the SUNY Molecular Analysis Core, said. "We can do that PCR almost instantaneously, after we have the pellet. About 12 minutes later -- by lab standards, it's almost instantaneous -- (we have the results)."
Data from sewage can give a sense of how many people have had Covid-19 asymptomatically.
Green, a microbiologist at the SUNY College of Environmental Science and Forestry, said the entire testing process would most likely take close to four to eight hours because of what's entailed in actually collecting and filtering out the wastewater samples.
But he said the difference in hours of testing for Covid-19 presence regularly -- compared to testing only symptomatic patients when there are spikes in cases -- could be a major deterrent in reducing hotspots both now and in a potential second wave.
"In some areas, it's not practical," Green said. "But in a lot of areas, it is. If you have surveillance set up ahead of time and can crank it up at the beginning when you first hear about the possibility of an outbreak, you can use the platform as an early warning system. That would give us days or weeks lead time in coping with the pandemic or epidemic."
Scientists in other countries have also been using their sewerage systems to mass test for Covid-19, though they express caution on how accurately wastewater samples reflect community levels of the virus.
In early April, the journal Nature reported that more than a dozen research groups around the world were analyzing wastewater for Covid-19, with traces of the virus found in wastewater in the US, Netherlands and Sweden.
The Netherlands' National Institute for Public Health and the Environment said in a statement last month that coronavirus had been detected in a wastewater sample taken four days after the country's first confirmed case.
"A small percentage of patients with Covid-19 have the novel coronavirus in their gastrointestinal tract, and thus excrete it in their faeces," the institute said in a statement, issued on March 24.
The wastewater testing approach had previously been used to detect viruses such as polio and measles, the statement said.
The Italian Institute for Health (ISS) reported last week that wastewater samples had returned positive results for parts of Milan and Rome. It said the RNA that was detected did not necessarily represent live, infectious virus.
"The result reinforces the prospects of using urban center sewage control as a non-invasive tool for early detection of infections in the population," the ISS said in a statement. "In Phase 2, surveillance can be used to indirectly monitor the circulation of the virus and to early detect its possible reappearance, thus allowing to recognize and circumscribe any new epidemic outbreaks more quickly."
Australian researchers have also found traces of the virus in sewage and said they are working towards a national testing program.
"The hope is eventually we will be able to not just detect the geographic regions where Covid-19 is present, but the approximate number of people infected -- without testing every individual in a location," the head of Australia's national science agency -- CSIRO -- said in a statement issued on April 16. "This will give the public a better sense of how well we are containing this pandemic."
In neighboring New Zealand, scientists at the state-owned ESR said they are testing wastewater for Covid-19 to try to gauge the effectiveness of eradication efforts and better understand the patterns of community transmission.
"We're collaborating with research organizations here and internationally and contributing to the global effort to learn more about Coronavirus and ultimately find a vaccination," said ESR Chief Scientist Brett Cowan in a statement earlier this month.
But the ESR researchers noted that Covid-19 was a respiratory illness and "unlikely to be spread by contaminated faeces," suggesting levels of the virus would be low and hard to detect.
CNN's Livia Borghese and Sharon Braithwaite also contributed to this report.