SINGAPORE - On Jan 2, the Mandarin Orchard Singapore hotel was allowed to reopen.

It had been closed for 14 days after a cluster of Covid-19 cases from 10 countries was discovered on site.

The outbreak at the hotel led to 394 guests and 571 staff being swabbed for the coronavirus.

Experts have cautioned that the cluster is a reminder of how easily the virus can spread, a timely warning even as crowds of people gathered over the long New Year's weekend.

The Straits Times looks back on this latest cluster here:

On Dec 19, 2020, the Ministry of Health (MOH) announced that it was probing 13 cases of Covid-19 among people who had served their Stay-Home-Notices (SHN) at Mandarin Orchard Singapore.

The National Public Health Laboratory (NPHL), which conducts whole genome sequencing and phylogenetic analysis on all Covid-19 cases, found that the 13 imported cases - who were confirmed to be infected in early November - were infected by coronavirus strains that have high genetic similarity.

This was despite the guests flying in from different countries, implying that the infections may have come from one source.

The 13 guests had all served their SHN in the same tower of the hotel between Oct 22 and Nov 11, 2020.

The hotel stopped accepting new guests with immediate effect on Dec 19, 2020, and those serving SHN at the hotel were moved to another facility, with guests being checked out progressively.

No staff tested PCR positive, but 11 had positive serology test results. However, several other guests had positive PCR results.

On Jan 1, MOH said it had concluded its investigations into the initial 13 cases and found that there was no transmission beyond them, and that other Covid-19 cases serving SHN at the hotel were not linked to the original 13 people.

"In view that the premises have been thoroughly disinfected, and there is no longer risk of transmission to hotel guests, MOH has approved the re-opening of Mandarin Orchard Singapore," said the ministry.

But it is still not known how the people got infected. Experts ST spoke to previously said that the human factor was most likely to blame for the spread if it had taken place within the hotel, although they could not be sure how it occurred.

Thus far, the authorities have not announced the discovery of any lapses or breaches in protocols at the hotel.

Commenting on the incident on Dec 22, Minister for Education Lawrence Wong, the co-chair of the task force tackling Covid-19 here, said: "What happened in Mandarin Orchard is yet another reminder that things can go wrong."

He added: "And that's why, once again, all of us need to take this seriously and remind ourselves why we should stay vigilant, stay alert and keep our guard up."