Eight more hotel staff at Mandarin Orchard Singapore, after taking serological tests, have tested positive, indicating likely past infections of Covid-19, said the Ministry of Health (MOH) yesterday afternoon.

They are in addition to the three cases announced on Sunday. Epidemiological investigations of these 11 cases are in progress, the ministry said.

Meanwhile, the ministry is testing their identified close contacts as a precautionary measure. It will also conduct serological tests to determine if these individuals could have been infected by the 11 cases.

These cases were excluded from the Covid-19 daily count, the ministry said, as their polymerase chain reaction (PCR) test results are negative for the infection, indicating these are likely to be past and not current infections.

The ministry said: "Singapore reports Covid-19 cases in accordance with international practice. Every case who tested positive through a PCR test and is assessed to be an acute infection is reported and included in our case count.

"We follow the World Health Organisation's criterion that only positive results from confirmatory tests (that is, PCR tests) are included in the case count."

In total, MOH has tested 571 staff of Mandarin Orchard Singapore, and all the PCR test results have come back negative for Covid-19 infection.

This means there is no ongoing infection among staff of the hotel.

Special testing operations to test all individuals and staff at Mandarin Orchard Singapore have been completed, it added.

In total, 394 persons serving stay-home notice (SHN) at the hotel have been swabbed. Of these, three tested positive on Sunday and were immediately sent to hospital in an ambulance.

These cases were included in the ministry's daily case count on Sunday. As they have recent travel history, it is likely these are imported cases who were infected while they were overseas, said the ministry.

However, the National Public Health Laboratory will conduct whole genome sequencing and phylogenetic analysis to determine if they could be linked to 13 other cases.

Last Saturday, MOH announced that it was investigating 13 cases of Covid-19 infection among individuals who had served SHN at Mandarin Orchard Singapore between Oct 22 and Nov 11.

They were from 10 different countries and MOH is investigating if they are linked because they were infected by coronavirus strains that have "high genetic similarity", implying that the infections may have come from the same source.

As a precautionary measure, all existing guests at the hotel were checked out by 9pm on Sunday.

Those serving SHN there were taken in dedicated vehicles to an alternative dedicated SHN facility on the same day, said the ministry.