SINGAPORE - The number of sites under wastewater testing surveillance for Covid-19 is set to double by next year, said the National Environment Agency (NEA).
Currently, more than 200 sites - including workers' dormitories, hostels, nursing homes and residential areas - are under surveillance, with 2,500 samples processed per week.
The frequency of sample collection varies from site to site and depends on the purpose of the surveillance programme, NEA said on Wednesday (July 7).
Dr Judith Wong, director of the microbiology and molecular epidemiology division at NEA's Environment Health Institute, said infected individuals may shed Covid-19 viral fragments in their stool or sputum - a mix of saliva and mucus.
At a media briefing in Beo Crescent on Wednesday, she demonstrated the use of an autosampler - a device pre-programmed to draw wastewater samples for testing.
The device allows NEA to customise the sampling programme, and make adjustments depending on whether it intends to take samples throughout the day or during peak sewage activity.
Wastewater testing is a non-intrusive surveillance strategy that complements swab operations and clinical testing in detecting Covid-19 transmission.
It was first used here in February last year to monitor the spread of Covid-19 in dorms.
Today, with dormitories largely free of the virus, the surveillance programme complements rostered routine testing of dorm residents for early detection of Covid-19 transmission, which facilitates intervention and isolation of cases.
Wastewater surveillance was expanded to residential areas in July last year, starting with Tampines. This detected a new Covid-19 case at a residential block, said NEA.
Subsequent detection of viral fragments in Hougang, Yishun and Bukit Merah triggered mass swab tests for residents and visitors at Housing Board blocks in those neighbourhoods.
Wastewater testing detected more than 15 cases last month, NEA said.
Detecting no viral fragments, on the other hand, provides added assurance that those tested sites are free from infection.
The exercise allows the authorities to direct testing resources in a more targeted manner.
In areas where Covid-19 clusters are present, wastewater surveillance is conducted for a period of time until the wastewater samples test negative.
NEA also conducts wastewater testing at "regional nodes", which it did not name, across different parts of Singapore. This enables broader surveillance of the community.
"Information collected from these sites provides a sense of the prevalence of infections in the community," the agency said.
It likened the surveillance at these regional nodes to the testing of wastewater samples from water reclamation plants.
Sites are identified based on factors including the suitability of the sewage network for sampling, the likelihood of viral shedding in waste from the population sampled, and the ability to trace and identify new infections at the sites surveyed.