Across the United States, scientists have been analyzing sewage water to determine how intense outbreaks might be, given limits on testing, or to predict where the next one might be brewing. Sewage tests cannot identify individual cases but can help some communities, such as universities, respond to outbreaks in particular areas or buildings.
Elsewhere in the world, countries have been expanding their use of sewage sampling. Here are some of their key findings.
Every morning at 5, a group of scientists in Ottawa receives samples of the previous day’s sewage to test for traces of the coronavirus in wastewater pooled from “over a million souls,” said Alex MacKenzie, a senior scientist at the CHEO Research Institute.
MacKenzie is part of a team at CHEO and the University of Ottawa that piloted the program, which Ottawa’s public health department uses to provide daily reports on the coronavirus’s spread. In early October, MacKenzie’s team reported that concentrations of the virus in the area’s wastewater had doubled in the past month and increased tenfold since June.
Other cities and provinces across Canada, as well as several universities, are watching sewage systems for signs of the virus.
Such testing provides crucial information at little cost, MacKenzie said. Each sample costs only several hundred dollars and gives a reliable snapshot of the big picture, and there are few privacy concerns because the tests do not detect individual infections.
“There’s a general realization that we should be doing this as much as possible,” he said.
The model could have applications for vulnerable populations, he said, such as those living in homeless shelters, prisons and elder-care homes, if plumbing systems in buildings or apartment blocks were frequently tested.
While many countries and cities test wastewater for virus RNA, MacKenzie said his team is also looking for the protein that surrounds the genetic matter. The virus’s RNA, he said, “is a fragile beast,” while the protein is sturdier and could provide an even more accurate picture of the virus’s spread.
In early February, over a month before the global pandemic was declared, scientists from the Dutch KWR Water Research Institute in Nieuwegein began periodically testing sewage samples from seven cities and one airport, according to a paper they published in July. Initial tests came back negative. But on March 5, Dutch scientists detected the coronavirus in wastewater at a treatment plant in the city of Amersfoort, about 32 miles southeast of Amsterdam. Weeks later, Amersfoort’s first case of the virus was confirmed.
Since March, the Dutch National Institute for Public Health and the Environment has been taking weekly samples from sewage systems across the country. As in the first study, researchers were able to detect small traces of the virus before cases or outbreaks were confirmed. While the program began with a few dozen sites, since Sept. 7 the institute has been testing systematically each of the country’s more than 300 sewage treatment centers, according to its website.
During the 2003 SARS outbreak, researchers in Hong Kong were puzzled by the question of how the virus had infected hundreds of people in a 33-story apartment building. Their conclusion: SARS, a coronavirus related to the one causing covid-19, had probably aerosolized and spread through the plumbing system. Scientists narrowed in on a patient zero, who had diarrhea in a bathroom in the building, where the plumbing was faulty.
The U.S. Centers for Disease Control and Prevention reports it is “unclear whether the virus found in feces may be capable of causing covid-19.” But researchers from the early days of the pandemic have been studying the novel coronavirus’s genetic matter in the fecal matter of patients.
Scientists in Hong Kong were curious whether testing stool samples from certain populations might aid in detecting the virus better than diagnostic tests, which can produce false negatives. In a report in September, researchers at the Chinese University of Hong Kong concluded that this approach could be useful for identifying asymptomatic cases, as the virus may still be detectable in stool samples after it’s gone from a patient’s respiratory tract, Reuters reported.
The researchers, who began the study in March, also advised that stool samples could be useful for testing infants and others for whom taking a nose swab is difficult. They found that infants and children tended to have higher viral loads in their fecal matter, compared with adults. Scientists are expanding the study.
In addition to tracking outbreaks, researchers are interested in what evidence about the origins of the pandemic sewage can provide. In northern Italy, where the coronavirus took a heavy toll in March and April, scientists from the Italian National Institute of Health analyzed sewage samples collected from 40 wastewater treatment centers between October 2019 and February 2020.
The coronavirus, they found, was first detected in samples from Milan and Turin on Dec. 18, nearly two weeks before China reported that a mysterious virus was circulating in the city of Wuhan.
The Finnish National Institute for Health and Welfare announced April 22 that it would begin to monitor for the virus in sewage systems across the country.
In August, after a decline in cases over the summer, the institute issued a warning: The virus had been detected in sewage water from five new locations. "The area may contain unidentified infected people and the virus may be spreading in the population of the area,” Tarja Pitkänen, a senior researcher at the institute, said in a statement.
In the coming weeks, cases increased. In early October, the institute warned the spread of the virus was “clearly accelerating.” Even with the uptick, Finland’s coronavirus count of just over 14,000 confirmed infections is relatively low.