COVID-19: Screening of dormitory wastewater effective, more testing to be done

The NEA has initiated a pilot surveillance programme to screen wastewater samples for SARS-CoV-2, the virus causing COVID-19. (PHOTOS: NEA)
The NEA has initiated a pilot surveillance programme to screen wastewater samples for SARS-CoV-2, the virus causing COVID-19. (PHOTOS: NEA)

SINGAPORE — A pilot programme, launched here in February, to screen wastewater samples for the novel coronavirus, can play a big role in monitoring and managing COVID-19 transmission in the community as well as among workers in dormitories.

Led by the National Environment Agency (NEA) – and supported by the Public Utilities Board (PUB) and Home Team Science and Technology Agency (HTX) – a team of scientists has been sampling wastewater in manholes of 20 large foreign worker dorms and water reclamation plants, the agencies announced in a joint statement on 19 June.

The levels of COVID-19 viral ribonucleic acid (RNA), or viral material, were detected in these samples in late March – correlating with the spike in cases detected in dorms – while they were undetected in samples taken on 9 March when there were 160 reported cases, the statement said.

The results show that the concentration of COVID-19 viral material in wastewater is related to the prevalence of COVID-19 in the dormitories, it added.

The programme was first mentioned by National Development Minister Lawrence Wong, also co-chair of the COVID-19 multi-ministry taskforce, during his televised speech last Tuesday.

It provides “an additional indicator” that complements the clinical tests to assess the COVID-19 situation and guide the progressive clearance of the dorms, said the agencies. It can also guide the necessary response plans and mitigation actions required – such as individual testing and isolation – the agencies added.

For instance, for dorms with no detected COVID-19 cases in the pilot programme, a zero reading for COVID-19 viral material in their wastewater “provided the added assurance” that they remain free from infection.

For dorms where viral material was detected in their wastewater, more swab tests were conducted for workers living there, leading to more detections and isolation of cases, including asymptomatic ones, said the agencies.

These samples can also capture information on a cross-section of the community, which allows for the monitoring of large groups. Likewise, clinical testing for COVID-19 can be carried out for the affected community, allowing screening for COVID-19 to be carried out in a more targeted manner.

“The team has thus far demonstrated the utility of wastewater testing as a warning system for the presence of the COVID-19 cases, and that the trending of SARS-CoV-2 concentration over time can determine if infection control measures taken have been effective,” the agencies said.

More research needed

However, while the agencies noted that the approach has been useful in detecting COVID-19 cases, “more research is needed to understand the sensitivity of the method in detecting early or a few number of cases”.

“Despite its potential, the use of wastewater surveillance to detect COVID-19 spread is still in its early stages,” they said, adding that the NEA is working to increase coverage by expanding its sampling to more wastewater nodes.

“More information on the results of the wastewater surveillance in Singapore will be revealed when ready.”

The agencies also noted that at low-level transmission, wastewater surveillance appears to be less sensitive than clinical surveillance of cases in Singapore.

“This is likely due to our intensive clinical testing regime. Monitoring is ongoing to determine the trending of the concentration of viral material at the water reclamation plants, and the relationship between the viral material concentration and prevalence of COVID-19 in Singapore,” said Associate Professor Ng Lee Ching, director of the NEA’s Environmental Health Institute.

The agencies also explained that the detection of viral material, or RNA, in the wastewater does not suggest the presence of viable or infectious virus.

Without a host, the virus will not be able to propagate over time in wastewater, they added.

As an added preventive measure, wastewater from locations with COVID-19 cases – such as hospitals, isolation facilities and dorms – are disinfected with chlorine at the premises before they are being discharged into the public sewers.

To date, Singapore has 41,615 cases of COVID-19, including 39,223 foreign workers living in dorms.

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