10 cases of Covid-19 detected in Hougang block, affected residents from same stack on different floors

10 residents of an Hougang block have tested positive for Covid-19, including one case which was detected after two days of mandatory swab tests were carried out, reported The Straits Times. 

The Ministry of Health had announced on Thursday (May 20) that residents of Block 506 Hougang Avenue 8 had to undergo tests for Covid-19 at the void deck of the block on Friday and Saturday, after some residents were found to have tested positive for the virus.

The Ministry of Health and National Development Ministry issued a joint statement on Sunday (May 23), stating that polymerase chain reaction (PCR) testing for 407 residents and visitors have been conducted, with another 126 test results pending.

The cases detected are largely among those who have already been quarantined who later tested positive for the virus.

"This means that they have been isolated early and ring-fenced, and were not likely to be moving around while being infectious."

According to the statement, residents who tested positive for the virus reside in four different units from the same stack — directly above or below each other — in the 12-storey block.

One of the cases at the block is believed to be a security officer from the Changi Airport cluster, reported Lianhe Zaobao yesterday. His wife and daughter also tested positive for the virus.

Another case is a 50-year-old woman living in the block, along with two other suspected cases residing in separate units.

Zaobao reported that one resident who was served the quarantine notice on Wednesday expressed puzzlement that only her maid was not required to serve quarantine, unlike the rest of the household.

A male member of another family had also received a quarantine notice on Thursday, but his father and brother living in the same unit did not. 

MOH said despite the affected cases being directly above or below each other, its initial assessment is that airborne transmission along the stack is highly unlikely. But it added that "epidemiological investigations are ongoing to determine linkages and the source of transmission".

Cleaning measures have also been stepped up to disinfect the block, MOH said.

The statement also noted that the Hougang block is the only HDB block with infected cases seen in more than two households so far.

Do lifts and sewage systems pose transmission risks?

In an article published in Zaobao on Saturday, infectious disease physician Dr Leong Hoe Nam from Mount Elizabeth Novena hospital said that lifts carry a high risk of transmitting the virus as it is an enclosed space, much like airplanes, buses and cars.

However, Professor Teo Yik-Ying, dean of the Saw Swee Hock School of Public Health at the National University of Singapore, said that even though lifts and lift lobbies are the most likely places where residents would come into contact with one another, more conclusive evidence through epidemiological studies would be required to establish a link.

As to whether the virus may be spread through wastewater, Dr Leong pointed out that while the sewage system has often been pinpointed as a possible transmission risk, this has yet to be proven conclusively.

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The Zaobao report highlighted that last year, residents living in a Hong Kong housing block were forced to evacuate after an explosion of coronavirus cases in the block. Design problems were subsequently found in the estate's sewage system, which was posited to exacerbate the spread of the virus. One expert who inspected the site drew parallels to the case of another Kowloon Bay residential estate which was hit by a major outbreak of severe acute respiratory syndrome (Sars) in 2003.

The results of a study into the Sars cases then found that there was a safety risk for residents living in flats facing the same direction. But the professor added that the virus could also spread through other means, or through an effect called "upstream influence" where air moves upwards against a wall.

Zaobao indicated that it had asked the Public Utilities Board (PUB) in March last year about the possibility of the virus being transmitted through sewage pipes. The PUB said then that the drainage systems of all home and buildings take into consideration public health factors and it is extremely unlikely that a similar incident would occur.

Residents of Block 506 in Hougang also revealed that the toilets in the block had just been renovated the year before.

candicecai@asiaone.com