Singapore is checking waste water with people’s poo for coronavirus

Experts say testing raw sewage is based on a ‘peculiar habit’ of the coronavirus – that it is shed in stools
Like Australia, the city state wants to monitor community transmission especially among people who are infected but do not yet know it

Coronavirus pandemic

Dewey Sim

Published: 7:30pm, 10 Jun, 2020

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From mass testing tens of thousands of its migrant workers to using serological tests to uncover links between its virus clusters, Singapore has deployed varying methods to stem the spread of the deadly coronavirus. But it is adding to this list a new method of detection: testing sewage for traces of the virus.

National development minister Lawrence Wong, who co-heads a multi-ministerial task force that deals with the virus, on Tuesday said the city state was now testing waste water extracted from manholes for viral fragments.

“This provides an additional indicator to tell us if a specific group, such as those living in a dormitory, has infected people among them,” he said during a national address.

Singapore, with 38,965 infections, last week lifted parts of its partial lockdown but the authorities have stressed that the easing of its measures would be a gradual, cautious one amid fears of a second wave of infections.

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Officials have attributed its dramatic surge in coronavirus cases to the aggressive testing of low-wage migrant workers in cramped dormitories, who now make up more than 93 per cent of its total infections.

The testing of raw sewage is not new. Australia in May said it intended to roll out a vast programme of raw sewage testing for virus traces in waste water and excrement, so it could focus testing and tracing on problem neighbourhoods. Officials said they were looking to monitor samples from some 71 per cent of people in Victoria, one of Australia’s most populous states. “So the whole point of this is to be vigilant and to find undetected cases or re-emergence,” Nicholas Crosbie of Melbourne Water said.

A trainee hydrographer takes samples from a sewer in Melbourne as part of a testing programme aimed at finding hidden clusters of the coronavirus. Photo: AFP

While sewage testing would not replace traditional testing methods, Abrar Ahmad Chughtai, an Australia-based epidemiologist, said that it would be an additional strategy to measure the level of community transmission.

“Although this does not provide a definite answer, it may provide additional evidence of infection in the community, particularly if asymptomatic transmission is ongoing in some locations,” said the lecturer of international health at the University of New South Wales, pointing to how recent studies had shown a “good correlation” between positive tests in faecal samples and the number of coronavirus cases in a given community.

Abrar said sewage was also commonly inspected for other infections, such as hepatitis A and E, as well as polio.

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Leong Hoe Nam, an infectious diseases expert in Singapore, said waste testing made use of a “peculiar habit” of the coronavirus, which is that it is shed in stools. “The value of it is that it identifies groups of people infected but not yet presented to the emergency department meaning you could potentially predict new clusters,” he added.

However, he said there were restrictions to the method. For example, if faecal matter extracted from a particular sewer tested positive for the virus, this could mean that hundreds of residents living in that area could have the virus.

“We can notify doctors and hospitals to be on alert and send reminders. But ultimately, finding that individual is like finding a needle in a haystack,” added Leong.

A cleaner outside Luk Chuen House in Sha Tin, Hong Kong, where a new outbreak of coronavirus cases sparked fears the virus could spread through structural problems in the buildings. Phot: K.Y. Cheng

Meanwhile, in Hong Kong, a cluster at Luk Chuen House in Sha Tin last week involving five residents sparked fears that the virus could spread through structural problems in the building, such as damaged sewage or ventilation pipes.

This was the case for a cluster among residents of Amoy Gardens in Kowloon during the Severe Acute Respiratory Syndrome (Sars) outbreak in 2003, when it was found the virus could have been passed through airborne faecal particles via sewage pipes.

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This month, authorities evacuated some 100 people from Luk Chuen House after several residents were infected with the coronavirus. Checks were done to see if sewage pipes were a route of transmission but leading infectious diseases expert Yuen Kwok-yung said a day later the cause of the spread could be due to kitchen exhaust fans.

Abrar, the epidemiologist, suggested that airborne transmission through sewage had occurred during Sars and “theoretically” this was possible with Covid-19 as well, though there was limited evidence that the coronavirus could be transmitted through aerosolisation of faecal material.

Leong, the infectious diseases physician, added that the World Health Organisation’s assessment was that Covid-19 was not airborne through faeces. The Amoy Gardens cluster in 2003 was an isolated incident, he said, and was not repeated or seen elsewhere.

For Singapore, this would be even more unlikely to occur. “Overall, Singapore has a very good sewage system and the waste gas discharge is limited or restricted,” he said.

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