SINGAPORE - The cluster of cases at the bus interchanges is likely to be a workplace transmission, though investigations so far have not identified specific modes of transmission, said Singapore's director of medical services Kenneth Mak on Friday (Sept 3).
"It is highly likely that spread has occurred within the work environment, possibly due to mask-off interactions during rest periods at the bus interchanges," he added.
The results of preliminary phylogenetic tests support the view that the cases are likely a workplace transmission event, Associate Professor Mak said at a press conference held by the multi-ministry task force tackling Covid-19.
Phylogenetic testing compares different virus genomes and helps scientists deduce the index case of a Covid-19 cluster.
The number of Covid-19 cases linked to eight bus interchanges has ballooned to more than 300 people.
The interchanges are: Toa Payoh, Boon Lay, Punggol, Jurong East, Bishan, Sengkang, Tampines and Clementi.
However, it is not clear how infection had first been introduced to the bus interchanges, said Prof Mak.
"But given the higher number of cases in the community presently, it is not unreasonable to expect that introduction of infection occurred from the community," he added.
He noted that some bus drivers may have become infected in the community, and then, in turn, infected other bus drivers in the interchange.
"We've also seen some infected bus captains bring infection back into their households, infecting their own household members," he added.
There is currently no evidence as yet of there being any passengers or users of public transport being exposed and infected with Covid-19, so the clusters still appear to be confined to the workplace at the bus interchanges, noted Prof Mak.
"The measures announced yesterday by the LTA will prevent potential further spread of infection at the workplace, which helps us to better manage the clusters," he said.
The Land Transport Authority on Thursday introduced a slew of tighter measures to curb Covid-19 spread at bus interchanges.
This includes segregating staff's resting and dining areas at bus interchanges, with only one staff member allowed to sit at each table for meals.
Bus drivers and staff manning service counters in bus interchanges will also have to undergo routine testing at least once a week.
"We are mindful of the need to be targeted and focused in our public health actions, so as not to unduly compromise essential transport services while seeking to disrupt further transmission at the interchanges," said Prof Mak.
He added that the Ministry of Health will continue to work closely with the LTA and the bus companies for bus drivers to be tested regularly using antigen rapid test kits, which will supplement the testing operations that are already being conducted at some of the bus interchanges.
More than 7,000 of the staff at the interchanges have been tested so far, with about 2 per cent of them having tested positive for Covid-19.
"It will take the rest of this week for the situation to stabilise and we anticipate that the number of cases from the interchanges may start coming down in the following week," he added.
Reiterating this, Health Minister Ong Ye Kung said that the number of new cases at the interchanges have been slowly coming down.
For instance, at Boon Lay Bus Interchange, there were 21 new cases on Monday, compared with five new cases on Friday. Similarly, Toa Payoh Bus Interchange had 20 new cases four days ago, compared with three new cases on Friday, Mr Ong noted.
"The cases are actually coming down, but the overall figures are going up, mainly contributed by unlinked cases and those needing classification, but these are not cases detected through swab operations at the bus interchange," he said.
He added that measures such as testing, isolating, contact tracing at the bus interchanges have been working in suppressing infections.