From the subarctic community in Yellowknife, Canada, to the subtropical city of Brisbane, Australia, scientists in more than 50 countries are now monitoring the spread of SARS-CoV-2 in wastewater. A number of wastewater monitoring programs monitoring COVID-19 have exploded over the past year of a dozen or more research projects for more than 200, after finding that whole virus particles and virus fragments are excreted in the faeces.
The information obtained helps researchers track cases, predict surges, identify where to focus on testing, and estimate the total number of infected people in cities or regions. Although wastewater monitoring has been used for decades to identify polio outbreaks and target immunization programs, and more recently to detect illicit drug use, the pandemic brought a new focus and investment in it as a means of monitoring public health.
“There has always been interest in the epidemiology of wastewater, but now it has started,” says Ana Maria de Roda Husman, a researcher at the Dutch National Institute for Public Health and the Environment in Bilthoven.
From the beginning of 2020, SARS-CoV-2 sewerage projects began worldwide, as wastewater experts focused on the crisis. However, the scope and focus of surveillance programs vary depending on how severely the countries or communities have been affected by the pandemic.
The number of ways wastewater monitoring is used is staggering. In the United Arab Emirates, researchers tested sewage from commercial aircraft to see if incoming flights carry infected passengers1. Researchers in Hong Kong are monitoring sewage in apartment buildings for undetected infections, and in Yellowknife, health officials are testing wastewater to find out which virus variants have entered their city, just 400 kilometers from the Arctic Circle.
Early warning system
One of the common applications of these monitoring programs is the early warning system. People who are infected start shedding virus fragments a few days before they show symptoms, and de Roda Husman uses this to predict the number of hospitalizations a few days in advance.
Other groups use wastewater to find and suppress outbreaks on a much smaller scale. At the University of California, San Diego, researchers are testing wastewater from 343 buildings around campus to check for signs of infection. Whenever a sample returns positive, the university will send targeted messages to encourage students located in affected buildings to test and isolate.
“You just can’t afford to test 10,000 students every day,” says Smruthi Karthikeyan, the university’s environmental engineer. Wastewater monitoring is a cheap and effective alternative that captures up to 85% of cases on campus.
A similar system is used in Hong Kong, where SARS-CoV-2 marks in the wastewater of two apartment buildings led to mandatory testing of all residents in January. According to South China Morning Post, an early warning system helped healthcare professionals find nine asymptomatic cases.
Researchers in Australia, where COVID-19 cases have remained relatively low throughout the pandemic, also use wastewater monitoring as an early warning system. In Queensland, wastewater samples are collected across the state and sent to a laboratory in Brisbane for analysis
However, small case numbers pose a unique challenge for Australian scientists. A typical way for scientists to collect wastewater samples is explained by David McCarthy, a water quality technician at Monash University in Melbourne, to take a bottle on a rope to a section of a sewer or treatment plant and throw it inside. says: “We are looking at maybe one or two cases of COVID in a million people. The chances of these cases escaping with this technique are really high. “
Instead, Australian scientists turned to other sampling methods. “Passive samplers” use gauze or other absorbent material that can be left in the wastewater for up to four days, increasing the likelihood of virus fragments being captured in this case by one to a million.
McCarthy has developed a small passive torpedo-shaped sampler that fits into narrow tubes. The plan is open-source and has been withdrawn in countries including Indonesia, New Zealand and Canada. And the interest in wastewater monitoring extends beyond academia to policy makers. “We met with ministers last week and were excited,” McCarthy said. “That would never have happened before a pandemic.”
Everywhere, governments and institutions have adapted existing wastewater monitoring methods to monitor larger trends in the number of cases in cities and neighborhoods. One of the countries leading the fee is the Netherlands.
Samples from wastewater treatment plants there allow scientists to estimate how many people in a large population are infected with SARS-CoV-2, and government officials use these estimates to decide whether to implement closures and how to direct resources.
Gertjan Medema, a microbiologist at the KWR Institute for Water Research in Nieuwegein, the Netherlands, argues that wastewater provides a more accurate overall picture of infections than diagnostic tests because it involves asymptomatic individuals. “Not everyone undergoes the tests, but everyone goes to the bathroom,” he says. “It’s nice to have an objective tool that doesn’t depend on being willing to take the test.”
Challenges for developing countries
However, more than 70% of wastewater monitoring programs are in high-income countries2, which poured resources into the epidemiology of wastewater. Many scientists in the developing world are struggling.
“Testing in India is incredibly demanding because sewer systems are fragmented,” said Sudipti Arora, an environmental scientist at the Institute of Biotechnology. B. Lala in Jaipur, India. Only about one-third of all cities have sewer networks, he says. “As a result, slums and rural areas remain largely untested.”
In the country’s two northern states, her team is testing hospital wastewater for SARS-CoV-2 to study whether specific disinfectants will deactivate the virus; as well as samples from sewage treatment plants to see if the method can be used more often in India. Despite the challenges facing the method in India, Arora and her team plan to use the experience gained in monitoring sewage during a pandemic in the future and apply it to detect other infectious diseases and antibiotic-resistant bacteria in wastewater.
Many scientists working in the field argue that a rare positive outcome of a pandemic may be that it normalizes the use of wastewater to monitor public health – whether future pandemics or other health indicators such as hormones that indicate stress or levels. caffeine consumption.
“The epidemiology of wastewater was under the radar,” says Karthikeyan. “It’s coming to the fore now.”