The COVID-19 task force is looking into the factors that might have led to the COVID-19 cluster at Tan Tock Seng Hospital (TTSH), said Associate Professor Kenneth Mak on Tuesday (4 May) at a press conference.
The Ministry of Health (MOH) director of medical services said that preliminary investigations suggest that there were not specific lapses in the processes and protocols among hospital workers that might have led to the cluster, though they are looking into various hypotheses including air flow and ventilation at the affected ward, Ward 9D.
Assoc Prof Mak said that the task force is not ruling out that the virus could have spread due to low mask usage by patients and visitors, as suggested by a reporter during the press conference.
The TTSH cluster now has 40 cases, including staff members, current and past patients, and visitors. There has also been on fatality—an 88-year-old patient who had been placed in Ward 9d from 14 April. On 8 April, it was confirmed that she had been infected with COVID-19. She died three days later due to complications from the virus.
According to MOH, the cluster popped up after a nurse assigned to that ward was tested positive for the virus on 27 April after developing symptoms.
The task force is investigating the reasons why the virus spread so quickly around the ward and whether it had anything to do with the hospital’s standard operating procedures, said Assoc Prof Mak. However, he noted that the authorities could not give definitive answers just yet as investigations were still incomplete.
Assoc Prof Mak said, “We are looking at various possibilities. Of course, (the reporter has) mentioned one — is it because of not wearing masks or a lack of discipline in maintaining discipline in infection control?”
Noting that as the cases were clustered around this one ward, the task force is also exploring the possibility of other local influences that might have contributed to the super-spreading even. This includes air flow and ventilation.
“We are exploring all possibilities and we are taking precautions accordingly, as we manage existing patients admitted in Tan Tock Seng Hospital,” he said.
No substantial evidence that COVID-19 spreads through ventilation systems
The fact that the task force is looking into air flow and ventilation as a possible factor that led to these cases in TTSH does seem odd, however.
In May 2020 when the world was still trying to figure out how COVID-19 spread, Executive director of the National Centre for Infectious Diseases (NCID) Professor Leo Yee Sin has said that there was no evidence that the virus could spread through air conditioning systems.
Prof Leo had cited a study by NCID researchers which found that the COVID-19 virus was found in air ducts connected to the room of one of the patients at an isolation facility, though it does not prove that the disease is airborne.
The study, which was published in the Journal of the American Medical Association, suggested that “small virus-laden droplets may be displaced by airflows and deposited on equipment such as vents”.
However, Prof Leo stressed that the study merely shows that the virus is scattered around isolation facilities, not that it is airborne.
At the time, Assoc Prof Mak had also clarified that the reason the virus was found in vents at the isolation facility had to do with the location of the vents. Where air conditioning units are generally located at the top of a room, in isolation rooms, the vents are located at the bottom.
He explained, “So when you take a swab and find viruses around the vents, it is actually a combination of droplets falling by gravity into those areas, as well as a bit of airflow that comes through.”
He added, “It’s not the same situation as in a home where you have an air-conditioning vent and you assume therefore it’s airborne. This is not. This is predominantly still droplet transmission.”
Since that paper was published, several other researchers have shared their own opinions and studies on the matter of air conditioning as possible routes of transmissions.
Unfortunately, the data has so far been inconclusive. Though the US Centres for Disease Control and Prevention (CDC) said on their website that while the virus has been detected in ventilation systems, “detecting viral RNA alone does not imply that the virus was capable of transmitting disease.”
It went on to highlight a study showing that the concentration of viable virus detected in the air of a COVID-19 patient’s room “was believed to be too low to cause disease transmission.”
It added, “While airflows within a particular space may help spread disease among people in that space, there is no definitive evidence to date that viable virus has been transmitted through an HVAC system to result in disease transmission to people in other spaces served by the same system.”