Bus interchange clusters: Workplace transmission via "mask-off interactions" a likely source, says Kenneth Mak

Cases linked to the bus interchange clusters likely surfaced from "mask-off interactions" at the workplace during rest periods, said Singapore's director of medical services Kenneth Mak on Friday (3 Sep).

This possibility is backed by results from preliminary phylogenetic tests, he told a press conference by the COVID-19 multi-ministry task force.

Such tests compare different virus genomes and lead scientists to the index case in a particular cluster.

300 cases have been identified so far in relation to the bus interchange clusters.

The interchanges are Toa Payoh, Boon Lay, Punggol, Jurong East, Bishan, Sengkang, Tampines and Clementi.

However, Assoc Prof Mak did not rule out community transmission as the origin of the bus interchange clusters, "given the higher number of cases in the community presently".

Some bus captains may have been infected from members of the community and might have then passed on the virus to other bus captains in the same interchange.

"We've also seen some infected bus captains, bring infection back into their households, infecting their own household members," he said.

Over 7,000 staff members at the bus interchanges have been tested so far, with about 2 per cent of them having tested positive for the coronavirus.

So far, there are no indications that any passengers or users of public transport have been exposed and infected as a result of the bus interchange clusters, said Assoc Prof Mak.

The clusters "still appear to be confined to the workplace at the bus interchanges", he said, adding that the new measures announced by the Land Transport Authority will prevent further transmission.

"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," said Assoc Prof Mak.

Health Minister Ong Ye Kung echoed Assoc Prof Mak's statement, saying: "Actually, the number of cases at the bus interchanges are coming down, but the overall figures are going up."

At Boon Lay Bus Interchange, there were 21 new cases on Monday. On Friday, in comparison, there were five new cases, he said.

Toa Payoh Bus Interchange had 20 new cases at its peak four days ago. In contrast, on Friday, there were three new cases, Mr Ong noted.

The rise in cases, he said, mainly come from the presence of unlinked cases and those needing classification.

Such cases, however, "are not cases detected through swab operations at the bus interchange," said Mr Ong.

Continuous testing, isolating, and contact tracing have succeeded in containing the spread of COVID-19 at the bus interchanges, he added.

Separately, Transport Minister S. Iswaran on Friday also said that there is no evidence yet showing that COVID-19 clusters in bus interchanges have resulted in the spreading of the deadly coronavirus to commuters.

“The experts have said that there is no evidence of any spread to commuters but we will make sure we observe all the safeguards that have been put in place,” Mr Iswaran told the media on the sidelines of Land Transport Industry Day at the Land Transport Authority (LTA) office in Bedok.

The priority right now is to ensure that both transport workers and commuters are safe, he said, adding that the public transport system continues to function.

“If there is a need to do more, the LTA will work with public transport operators to do so.”