Coronavirus: Singapore

Two more cases detected during testing at Hougang Ave 8 block

Total tally now 11 with 403 out of 405 testing negative; MOH says airborne transmission 'highly unlikely'

Two people have tested positive for Covid-19 during a mandatory testing exercise for residents and visitors at Block 506 Hougang Avenue 8.

Nine cases were earlier identified by the Ministry of Health (MOH), bringing the total number of cases to 11 people across at least four different households so far.

Although four of the units with confirmed cases are in the same stack, meaning they share the same unit number but are on different floors, MOH said its initial assessment is that airborne transmission along the stack is highly unlikely.

Polymerase chain reaction (PCR) testing for residents and visitors was conducted at the block on Friday and Saturday, said MOH and the Ministry of National Development (MND) in a joint statement. As at noon yesterday, 403 out of 405 people had tested negative.

MOH said the cases detected are largely among people under quarantine who later tested positive, meaning they were not likely to be moving around while infectious.

"Epidemiological investigations are ongoing to determine linkages and the source of transmission," MOH added.

The Hougang block is the only Housing Board block with infected cases seen in more than two households so far, the ministry noted.

PCR tests are also being conducted for all 243 residents of Block 559 Pasir Ris Street 51, as four cases have been detected in two different households in the block.

Associate Professor Hsu Li Yang, an infectious diseases expert at the National University of Singapore's Saw Swee Hock School of Public Health, noted that MOH and MND have not disclosed whether the affected units in the Hougang block are directly above or below one another, or if there are unaffected units in between.

"If the floors are one above the other, then perhaps some quirk of ventilation or air conduction allows aerosol spread," he said.

"If they are in the same stack but on floors five and 10, for example, then it is unlikely."

Infectious diseases expert Leong Hoe Nam, from the Rophi Clinic at Mount Elizabeth Novena Specialist Centre, said lifts are one possible source of transmission within the same HDB block.

"We know, consistently, that enclosed places are of high risk, whether it is buses, planes or cars. Lifts are like vertically moving cars," he said.

Dr Leong pointed to a study published in the International Journal of Infectious Diseases last month that showed how the virus lingered in the air inside a car after it was driven for 15 minutes by a Covid-19 patient who was not wearing a mask. It found that samples of the virus could be detected at least two hours after the drive, suggesting the risk of transmission by aerosolised virus.

"We tend to be more lax in a private enclosed space.

"We may clear our nasal mucus, blow or dig our noses, or adjust our masks for a breather," Dr Leong said, adding that these lapses in people's usual behaviour could put them at risk.

In a Facebook post yesterday, Aljunied GRC MP Gerald Giam said MOH's measures have greatly reduced the risk of transmission among residents in the block, although it cannot be fully ruled out.

As an extra precaution, the Aljunied-Hougang Town Council disinfected common corridors and lifts at the block on Saturday evening, after the swabbing operation at the void deck was completed, he said.

He also said some residents at the block had been unable to receive deliveries such as cooking gas cylinders over the last two days.

"We have contacted the relevant company to encourage them to resume deliveries as soon as possible so that you can cook your meals."

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A version of this article appeared in the print edition of The Straits Times on May 24, 2021, with the headline Two more cases detected during testing at Hougang Ave 8 block. Subscribe