Lab work conducted to screen wastewater samples for SARS-CoV-2
The National Environment Agency (NEA) has initiated a pilot surveillance programme to screen wastewater samples for SARS-CoV-2, the causative virus of COVID-19. The amount of viral material in wastewater from a community could reveal the level of COVID-19 spread in the community, and trigger the necessary response plans and mitigation actions, such as individual testing and isolation. Supported by National Water Agency PUB and Home Team Science and Technology Agency (HTX), the novel approach has complemented the Inter-Agency Task Force’s efforts in assessing the situation and reducing the transmission of COVID-19 in the workers’ dormitories.
Led by the Ministry of Manpower and comprises the Ministry of Health, the Singapore Armed Forces and the Home Team, the Inter-Agency Task Force has been set up to support foreign workers and dormitory operators in managing COVID-19.
Gleaning information from wastewater
Wastewater surveillance is a promising method for assessing the COVID-19 situation, as infected individuals, including those with mild or no symptoms, could shed the virus in their stool. Since February 2020, scientists from NEA’s Environmental Health Institute (EHI), with scientific inputs from Singapore Centre for Environmental Life Sciences Engineering (SCELSE) and the Nanyang Technological University, Singapore-Massachusetts Institute of Technology Alliance for Research and Technology (SMART) and the National University of Singapore, have developed a methodology for wastewater sampling and testing for COVID-19.
With support from PUB and HTX, the team has been sampling wastewater from the Water Reclamation Plants (WRP) and workers’ dormitories. In the laboratory, a sensitive molecular assay is used to screen the samples and quantify the genetic material of the virus.
Results from the testing of the wastewater from the WRPs showed that the level of COVID-19 viral ribonucleic acid (RNA) was not detected when there were 160 COVID-19 cases reported nation-wide as at 9 March 2020. However, the RNA levels became detectable in late March 2020, which correlated with the increase in cases detected in foreign workers’ dormitories. This demonstrated the usefulness of wastewater surveillance as a monitoring tool for SARS-CoV-2.
“Several reports overseas have shown that wastewater testing at treatment plants could be useful for early detection of COVID-19 transmission in the community. However, at low level transmission, wastewater surveillance at the treatment plant 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 WRPs, and the relationship between the viral material concentration and prevalence of COVID-19 in Singapore”, explained associate professor Ng Lee Ching, director of NEA’s Environmental Health Institute.
The team conducting field work
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. As an added preventive measure, wastewater from locations with COVID-19 cases, such as hospitals, isolation facilities and dormitories, are disinfected with chlorine at the premises before discharge into the public sewers. Disinfectants like chlorine can effectively inactivate the viruses.
Wastewater testing to support dedicated efforts at workers’ dormitories
Testing of wastewater to assess the situation of COVID-19 in a community or geographical population catchment is not new. However, NEA’s EHI has brought the science of wastewater testing further by using it to support the Inter-Agency Task Force’s dedicated effort in monitoring and management of COVID-19 transmission among workers in dormitories (refer to Annex A for pictures of lab and field work). The pilot programme involves monitoring wastewater in manholes of 20 large dormitories to provide an additional indicator that complements the clinical tests to assess the COVID-19 situation and guide the progressive clearance of the dormitories.
For dormitories in the pilot programme with no detected COVID-19 cases, a zero reading for SARS-CoV-2 material in the wastewater provided the added assurance that the dormitories remain free from infection, and to allow the workers to leave the dormitories for work. On the other hand, viral material was detected in the wastewater of some dormitories, and this had prompted more swab tests for workers at these dormitories, leading to more detections and isolation of cases, including asymptomatic ones. This facilitated a more targeted swabbing strategy and contributed to the mitigation of further transmission.
The trial results at the dormitories also show that the concentration of SARS-CoV-2 material in wastewater is related to the prevalence of COVID-19 in the dormitories. 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.
Wastewater samples can also capture information on a cross-section of the community, which allows for the monitoring of large groups. If positive signals are detected from wastewater at a particular site, 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. Although 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. NEA is working to ramp up its capacity to increase its coverage by expanding sampling to more wastewater nodes, which would improve the ability to pick up transmission. More information on the results of the wastewater surveillance in Singapore will be revealed when ready.