Marc Johnson saw trouble in the water.
Johnson, a virus expert at the
University of Missouri, had spent
much of 2020 studying sewage, collecting wastewater from all over the state and
analyzing it for fragments of the coronavirus. People with COVID-19 shed the
virus in their stool, and as the coronavirus spread throughout Missouri, more
and more of it began to appear in the state’s wastewater.
اضافة اعلان
In January, Johnson spotted something new in his water samples:
traces of B.1.1.7, a more contagious variant that was first detected in
Britain. Officially, the state had no confirmed cases of B.1.1.7, but the
wastewater suggested that the variant had arrived. By the end of the month, the
B.1.1.7 levels in Johnson’s water samples had risen sharply, and in early February,
the state finally found its first case. It has since found hundreds more.
Using some samples of sewage, Johnson had been able to peer into
Missouri’s coronavirus future. “I can’t believe how well it works,” he said. “I
feel like an oracle.”
Johnson is one of many scientists who have been drawn into the
once niche field of wastewater epidemiology in the past year. Researchers in 54
countries are now tracking the coronavirus in sewage, according to the
COVID19Poops Dashboard, a global directory of the projects.
Their work has validated the idea that wastewater surveillance
can be a useful way to track infectious disease across entire communities,
revealing epidemiological blind spots and yielding actionable public health
information.
It has also helped push wastewater epidemiology into the
mainstream. In March, the European Commission recommended that member states
establish systems to monitor sewage for the coronavirus. And last fall, the
Centers for Disease Control and Prevention and the Department of Health and
Human Services established the National Wastewater Surveillance System to help
local officials respond to COVID-19. It is the first system of its kind in the
United States.
“Wastewater surveillance is not a new idea,” said Amy Kirby, the
program lead for the surveillance system. It has been used in low- and
middle-income countries in the fight to eradicate polio, for instance, and has
been proposed as a way to keep tabs on noroviruses, a common cause of stomach
bugs. “But really, the return on investment to build this large new
infrastructure was never enough to warrant building the system for any of those
other diseases,” Kirby said. “But COVID and the pandemic really changed the
calculus.”
The system, and others like it now emerging around the world,
could ultimately usher in a new age of wastewater epidemiology, helping
officials track not just the coronavirus, but also other outbreaks and
diseases. “I think this is really going to be the beginning of a whole new type
of data collection for public health disease surveillance,” Kirby said.
Getting Their Feet Wet
Although COVID-19 is primarily a respiratory disease, research
conducted early in the pandemic revealed that people infected with the
coronavirus often shed it in their stool. This finding,
combined with the scale and urgency of the crisis, spurred immediate interest
in tracking the virus by sampling wastewater.
By searching for, and then counting, certain coronavirus genes
in sewage, researchers hoped to determine whether the virus was present in a
particular region and how widespread it was. Before long, wastewater
surveillance projects were popping up everywhere from Kansas City, Missouri, to
Kathmandu, Nepal.
The resulting data, now appearing in a flood of scientific
papers and preprints, have provided powerful proof of principle. Scientists
have detected the virus in all kinds of environments: in treated and untreated
water, in sludge and settled solids, in sewers and septic tanks, in pit
latrines and open drainage systems. They found it in water flowing into
enormous treatment plants and out of schools, dormitories and nursing homes. “It’s
just fascinating how robust this tool has become,” said Peter Grevatt, CEO of
the Water Research Foundation.
Teams all over the globe — in the United States, France,
Portugal, India, Iran, Brazil, Canada and elsewhere — also found that the
wastewater data seemed to be an accurate indicator of what was happening in the
real world. When the number of diagnosed COVID-19 cases in an area increased,
more coronavirus appeared in the wastewater. Levels of the virus fell when
areas instituted lockdowns and surged when they reopened.
Multiple teams have also confirmed that sewage can serve as an
early warning system: Wastewater viral levels often peaked days before doctors
saw a peak in official COVID-19 cases.
This lead time, which can range from a couple of days to two
weeks, depends partly on the robustness of local clinical testing programs,
scientists say. When more people are being tested for the virus more
frequently, the wastewater data provides less advance warning. The lead time
also exists because infected people often begin shedding the virus, SARS-CoV-2,
before they feel symptoms and then, once they fall ill, frequently delay
seeking medical care.
“I think wastewater has proven itself as one of the most, I
would say, objective means of understanding what SARS-CoV-2 is doing in our
society,” said Gertjan Medema, a microbiologist at KWR Water Research Institute
in the Netherlands.
It has proved sensitive, too, allowing researchers to detect a
single infected student in a dorm or resident in a nursing home.
Plugging Holes
Wastewater surveillance is not a replacement for clinical
testing, experts said, but can be an efficient, cost-effective complement. In
one study published in August, researchers calculated that they could test the
wastewater from every treatment plant in Germany millions of times for less
than it would cost them to test every German resident just once. The approach
is likely to be especially valuable in low- and middle-income countries, where
testing resources are even more limited.
“Not every population gets tested, not everyone has access to
health care,” Johnson said. “If there’s groups of people that are asymptomatic,
they probably aren’t getting tested either. So you aren’t really getting the
full big picture. Whereas for our testing, everyone poops.”
In Australia, where case numbers have been relatively low, the
wastewater monitoring has helped reassure authorities that their pandemic
controls are working. “Almost all the samples come back with nothing in them,”
said Daniel Deere, the project manager for ColoSSoS, a coronavirus sewage
surveillance project in Australia. “It’s been good to give confidence to allow
the economy to stay open, to allow movement to continue between states.”
(On the occasions when a water sample has come back positive,
the government has ramped up testing and launched media campaigns to alert
people who live in the region, he said.)
Waste Not, Want Not
This flurry of research and investment has been a boon to
wastewater epidemiology. “This has been just an amazingly huge catalyst for the
field,” said Tim Julian, who leads the pathogens and human health group at the
Swiss Federal Institute of Aquatic Science and Technology.
Over the past year, scientists have refined their methods, and
water utilities, environmental laboratories and public health agencies have
forged new connections. “The big question mark on everyone’s mind is what
happens next,” said Christopher Mason, a geneticist at Weill Cornell Medical
College who is part of a team tracking the coronavirus in wastewater samples
collected from sites around the world. “How long does this go? How do we really
sustain it?”
The Centers for Disease Control and Prevention’s (CDC) new
wastewater surveillance system is one answer.
“A lot of the initial efforts were coming from academic
researchers, commercial laboratories and a few utilities that were able to do
the testing themselves,” Kirby said. “And they have done great work to develop
these methods. But routine, long-term surveillance work is not what any of
those groups were designed to do.”
The National Wastewater Surveillance System provides funding,
technical support, a national data repository and other resources that will
allow state and local health departments take over this long-term monitoring.
Since its founding last year, the system has grown to include 33 states, four
cities, one county and three US territories.
The European Union is also developing a “sewage sentinel system”
that aims to monitor the wastewater in roughly 6,000 cities, Medema said. Although
COVID-19 is the immediate priority, researchers are also assessing the
feasibility of using such a system “in a post-pandemic European Enion (EU) for
antibiotic resistance, infectious diseases, use of pharmaceuticals and illicit
drugs and maybe more on the horizon,” he said.
These systems could ultimately help officials stay ahead of
emerging threats, providing early warnings about whatever pathogen is poised to
cause the next pandemic. An Italian team recently found that the new
coronavirus was already present in the wastewater in northern Italy in
mid-December 2019, days before the first
COVID-19 cases in
Wuhan, China, were
publicly reported.
“This isn’t the last infectious disease that will come through
our water supplies,” said Belinda Sturm, an environmental engineer at the
University of Kansas. “This is a tool that we should make sure that we keep
sharpened.”
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