Wastewater monitoring
The Sims Bayou South Wastewater Treatment Plant and Sims Bayou river in Houston, Texas, US. City health officials and Rice University scientists have begun testing Houston wastewater samples for COVID-19, a process they hope will reveal the true spread of the new coronavirus as clinical testing continues to lag. Image Credit: AP

Poop data monitoring is a cheap and effective way to fight the spread of new coronavirus. That’s what scientists say, referring to wastewater analysis. The amount of virus found in sewage can often reflect the timing and scale of an outbreak. Which means it can act as an early warning system, besides alerting health officials of a new wave of infections.

Data harvested from wastewater can also indicate the extent of infections in a community. That will allow officials to make decisions on enforcing or easing lockdowns in an area.

Sewers provide near–real-time outbreak data as they regularly collect faeces and urine which can contain coronavirus shed by infected people, a report in the journal Science said. High concentrations of virus in wastewater indicate higher numbers of infected people who use the sewage system. And this will allow researchers to estimate the total number of infections in an area or a community.

More than a dozen research groups have been analysing wastewater for the SARS-CoV-2, and traces of the virus have been found in the Netherlands, Australia, France, the United States and Sweden. Researchers at the Khalifa University in the UAE too have been analysing wastewater for data on the coronavirus.

What is wastewater monitoring?

Called wastewater-based epidemiology (WBE), it involves real-time monitoring of influents at wastewater treatment plants. The data mined from the samples can help predict disease outbreaks, track drug abuse in a society and monitor antibiotic resistance.

The data has been found to be useful in preventing the spread of COVID-19. Developed countries employ it to overcome the coronavirus testing bottlenecks, and underdeveloped countries find it an useful tool in absence of adequate testing facilities, a report in the Science Daily said.

Wastewater monitoring is not new. This early warning system has helped catch norovirus, hepatitis A and other diseases around the world for decades. It has been used for decades to assess the success of vaccination campaigns against polio virus, says Charles Gerba, an environmental microbiologist at the University of Arizona in Tucson, United States.

“Everything ends up in the sewer,” Gerba told the Los Angeles Times. “Even herpes virus you can detect by molecular methods.”

How does it work?

In most countries tests are in short supply, so outbreak figures are based on computer modelling. Here's where wastewater analysis can be of help since it provides a clear image of the actual viral load in a community.

Here’s how they do it: Once the amount of viral RNA excreted in faeces is determined, extrapolate the number of infected people in a population from concentrations of viral RNA in wastewater samples.

“Using computer models that incorporate data on how many viral particles individuals shed, and how they become diluted in sewage, it is even possible to translate detected viral concentrations into estimates of absolute numbers of infections in a sewage system’s catchment area, Zhugen Yang, a biomedical engineer at Cranfield University’s Water Science Institute, told the Science journal.

Early warning system against COVID-19

Given wastewater monitoring’s ability to predict the timing and scale of outbreaks, it can work as an early warning system. “SARS-CoV-2 can appear in faeces within three days of infection, which is much sooner than the time taken for people to develop symptoms severe enough for them to seek hospital care — up to two weeks — and get an official diagnosis,” Tamar Kohn, an environmental virologist at the Swiss Federal Institute of Technology in Lausanne, told the journal Nature.

How a new infection wave can be predicted

Using wastewater analysis, scientists can detect the coronavirus if it returns to communities. If the data shows a  spike in the viral load, preventive measures can soon be initiated to stave off a second wave of infections. “This visibility is also going to help us predict a second wave of outbreaks,” says Sebastien Wurtzer, a virologist at Eau de Paris, the public water utility of the French capital.

How wastewater data can help ease lockdowns

It’s impossible to test everyone for coronavirus. So the data from wastewater surveillance can give public health officials a headstart to introduce or ease measures like lockdowns.

Analysis of sewage samples will indicate the true level of outbreak and the success of containment measures. When viral concentrations start dropping in samples, you know that lockdowns are working. It might even help draw up a timeline to ease lockdowns.

Wastewater analysis around the world

Researchers in France were successful in tracking the coronavirus across greater Paris. They sampled wastewater for a month and detected a rise and fall in the virus concentrations in the French capital that correspond to the outbreak.

In the United States, analysis of samples from more than 100 sewage treatment facilities in 30 states helped draw up accurate snapshots of the outbreak in local communities, The Verge reported.

The Netherlands too used sewage surveillance effectively. Analysing the water that goes to a treatment facility in a Dutch city, researchers discovered the presence of the virus days before any cases were officially confirmed. One treatment plant can capture wastewater from more than one million people, says Gertjan Medema, a microbiologist at KWR Water Research Institute in Nieuwegein, the Netherlands.

Wastewater monitoring could provide better estimates on the spread the virus than testing, because it can account for those who have not been tested and have only mild or no symptoms, says Medema.

In Australia, Bret Sutton, Victoria’s chief health officer, said sewage testing was “important” and would be rolled out across the state. He told The Guardian that wastewater testing is “another tool in our surveillance that will tell us how much virus is out there”.

“Even if we are not getting cases notified, if we detect it in sewage, we know that there are active cases out there,” he said. “It might tell us about places where we’ve got gaps in surveillance, that people need to come forward for testing or we need to look harder for active cases.”

Sewage surveillance in the UAE

Researchers from the Khalifa University’s Centre for Biotechnology and the Centre for Membranes and Advanced Water Technology, plan to set up a surveillance system for municipal wastewater in the UAE.

“Khalifa University aims to establish a surveillance system for COVID-19 in municipal wastewater streams, linking it with simulation models developed for predicting and controlling the spread of the pandemic, together with the health authorities,” said Dr Arif Sultan Al Hammadi, executive vice-president at the University.

After the levels of virus in sewage water is estimated, researchers hope to construct a model that predict the number of symptomatic and asymptomatic COVID-19 patients.

Downsides to sewage testing

The results have been encouraging, but sewage testing should not be seen as a panacea. It should be used to supplement a range of testing measures, experts say.

Some questions still remain: how much virus does each person actually shed per trip to the toilet, and how do you account for factors like rain and snow that might impact sample dilution?

The traces of the coronavirus in the wastewater tend to degrade, so the risk of infection is low. Researchers do take into account the dilution and degradation when estimating the viral load in sewage water.

All the studies in several parts of the world show that a routine wastewater monitoring system could help cities and states be more proactive in preventing future outbreaks.

The future

American environmental microbiologist Gerba, who has been studying coronaviruses in wastewater since the SARS outbreak, says molecular technology has made sewage testing much faster and relatively inexpensive when compared to traditional cell cultures that could take weeks to process.

“We’re having discussions on how to best do this in the future, how to organise it, how do we look at our preserved samples,” Gerba told the Los Angeles Times. “Everything we learn from this will probably benefit us in the future — maybe in the fall … everyone is worried about the virus coming back in the fall.”

From early warning to predicting the viral loads in a community and providing clues to a second wave of infections, sewage science has been a cheap and effective tool in battling COVID-19. Fine-tuning the techniques will only make waterwater surveillance better at safeguarding us from pathogens.