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A series of crucial setbacks in Covid-19 testing has made it difficult to keep up with the virus’ rapid spread, and has inspired some researchers to look to wastewater to help fill in the gap of measuring how prevalent SARS-CoV-2 is in a given community.
In a paper posted Tuesday to the preprint server medRxiv, researchers collected samples in late March from a wastewater treatment plant serving a large metropolitan area in Massachusetts and found that the amount of SARS-CoV-2 particles in the sewage samples indicated a far higher number of people likely infected with Covid-19 than the reported cases in that area.
Researchers from biotech startup Biobot Analytics, working with a team from Massachusetts Institute of Technology, Harvard, and Brigham and Women’s Hospital, estimate there were at least 2,300 people infected with Covid-19 in the area around the treatment facility. But at the time of analysis, which has not yet been peer-reviewed, there were 446 cases officially reported in that area.
“It was interesting that our estimation was definitely higher than the number of confirmed cases in the area,” said Mariana Matus, CEO and co-founder of Biobot, adding that public health officials had already considered the possibility that the actual case count was much higher than what had been confirmed.
The company shared the findings with local health authorities including the Boston Public Health Commission and the Massachusetts Department of Public Health. Their response was “extremely positive,” Matus said. “They could believe that [our] numbers could be correct and not out of the realm of possibility.”
In another preprint, which has also not yet been peer-reviewed and that was posted last week to medRxiv, researchers in the Netherlands similarly described detecting the novel coronavirus in sewage samples — sometimes even before public health officials reported the first diagnosed case of Covid-19 in a given community.
“Wastewater carries all [our] chemistry,” said Rolf Halden, an environmental health engineer at Arizona State University, who was not involved in either study. “Now we have evidence from two different geographic locations that the virus is detectable, and that’s good.”
The idea to begin testing wastewater for SARS-CoV-2 emerged after recent research revealed that virus particles could be shed through stool and other bodily fluids. Testing begins with collecting sewage samples from local treatment plants, and running them through a process that creates millions of copies of viral RNA to be able to study the pathogen in detail. Another process then looks for specific markers on SARS-CoV-2, to distinguish this particular virus from all the other possible microbes in wastewater samples.
Wastewater has been used in other ways as a public health surveillance tool. Biobot, which was spun out of MIT, has also been involved in efforts to detect opioids in wastewater, as a way to help communities track patterns of drug use and developing public health threats. European countries have long been involved in surveilling the spread of antibiotic resistance through wastewater. And sewage has been used to look for other emerging and known viruses, including polio.
The new research comes at an unprecedented moment in public health: The difficulty and expense of obtaining individual tests for millions of people combined with the virus’ rapid transmission means that public health officials are looking for other ways to grasp the scale of the spread. Clinical testing largely is for those with more severe symptoms, meaning those who are asymptomatic or have milder symptoms — but can still be contagious — often are missed.
In these instances, wastewater sampling could offer a community-level picture of how the disease has spread. A high concentration of virus particles in a given treatment facility would signal that Covid-19 is still a problem in the surrounding area. This could inform public health officials on distancing measures to implement and the kind of precautions health care workers ought to take.
Gertjan Medema, who led the Netherlands research, had been part of a World Health Organization expert team during the SARS outbreak of 2002-2003, during which patients experienced gastrointestinal problems such as diarrhea. As the current pandemic unfolded, Medema kept an eye on similar symptoms among Covid-19 patients.
“I was looking into the information that was coming out of China to see if there was any fecal shedding, which turned out to be the case, and if people had diarrhea, which also turned out to be the case,” said Medema, the chief microbiologist at KWR Water Research Institute in Nieuwegein in the Netherlands. And since Covid-19 seemed like it was headed to the Netherlands, he and his team began checking wastewater for the virus.
“We saw that the technology works, that you do find the virus, and that it’s quite sensitive [to finding the right virus],” said Medema. And in the case of at least one Dutch city, Amersfoort, Medema and his team detected virus particles in wastewater even before the city had reported any official cases of Covid-19.
Experts say wastewater detection of SARS-CoV-2 could act not only as a supplement to medical testing but as an early warning system. If, for instance, the virus’ transmission were to ebb in the coming months, continued wastewater-based monitoring could alert public health officials if and when the virus is circulating in a community again.
“What’s been clear is that we are always behind,” said Halden. “The virus is a couple of weeks ahead and with individual testing we’ll never get there.”
Still, questions remain on using wastewater-based testing for Covid-19.
“We lack critical information on how long people excrete viruses [after being infected], how much virus is being excreted, and over what periods of time,” Halden said. “Every infection also takes a different course and it’s difficult to know exactly how many particles are shed by any given person.”
These uncertainties are why Biobot reported a range of possible cases: It estimated that between 2,300 people and 115,000 were infected in the area served by the treatment plant where it tested. “All of this gets better with more data, more sampling [of more people], and different populations [from different wastewater plants],” Matus said, adding that the company is already working toward gathering more data.
Biobot recently launched a campaign to provide its wastewater sampling services for free to communities across the country. Matus said the campaign has now enrolled 100 treatment plants across 25 states, with the goal of partnering with 10,000 such plants by the end of next month. Others, including Halden at Arizona State, are also involved in coronavirus tracking efforts. Halden leads the Human Health Observatory at ASU, which has over 250 monitoring locations in the U.S. and 350 locations around the world to test wastewater.
“We’re not doing this just because we want to publish papers,” said Matus, adding that the company is working on getting the preprint accepted to a peer-reviewed journal. “We are doing this work because we think the data can be useful in guiding the response to the outbreak.”