Experts say virus unlikely to spread through sewage system
Contaminated surfaces and residents visiting nearby blocks are more likely means of infection
Debunking fears that detection of Covid-19 in wastewater at residential blocks could mean the virus is being spread between blocks through the sewage system, infectious disease experts and the PUB said yesterday that it is highly unlikely residents could catch Covid-19 through the wastewater system.
On Monday, all residents of two Housing Board blocks in Hougang - 501 and 507 in Avenue 8 - were told to go for mandatory tests after Covid-19 viral fragments were detected in wastewater samples collected from the blocks.
The two blocks are within the area of Block 506 Hougang Avenue 8, which saw its residents mass-tested after a few of them contracted Covid-19.
Professor Paul Tambyah, president of the Asia Pacific Society of Clinical Microbiology and Infection, said: "Detection of Covid-19 fragments in wastewater does not mean that was the mode of transmission - it is a screening tool to pick up the presence of individuals who are shedding the virus."
In response to queries, a PUB spokesman said sanitary systems here are "closed systems" where the pipes are air- and watertight to ensure no foul air, viruses or bacteria can travel between households or blocks.
Professor Dale Fisher, an infectious disease expert at the National University of Singapore (NUS), said the infected residents of Block 506 may have transmitted Covid-19 to their neighbours in Blocks 501 and 507 through other means, such as contaminated surfaces.
Professor Teo Yik Ying, dean of NUS' Saw Swee Hock School of Public Health, said: "It could be that there are people asymptomatically infected in these blocks, and we should not rule out the possibility of false detection as well."
Testing for residents in the two blocks began yesterday and will end tomorrow.
When The Straits Times arrived at Block 507 in Hougang at about 9am yesterday, testing was in full swing and residents had formed a queue to get swabbed.
Madam Koh Beng Hup, who works at a McDonald's outlet, said: "I'm not worried about myself because I feel fine. But I'm worried someone in the block might have the virus.
"I've always been a careful person. I wash my hands when leaving home or coming back."
Separately, the National Environment Agency, which is in charge of wastewater testing for Covid-19, said that as at last month, it had expanded the wastewater surveillance programme to about 110 locations.
This includes Singapore's four water reclamation plants, workers' dormitories and other high-population density living premises such as nursing homes and student hostels.