The sole new coronavirus case announced yesterday is a work permit holder who arrived from Indonesia.

The foreign domestic worker had been placed on stay-home notice on arrival in Singapore and was tested while serving the notice.

Her serology test came back positive on Monday, which indicates a likely past infection.

However, she had not taken a serology test when she arrived in Singapore on Feb 2.

The Ministry of Health (MOH) said it was unable to definitively conclude she was no longer infectious when she arrived.

"As a precautionary measure, we will take all the necessary public health actions," it said.

The ministry added yesterday that one of the active clusters last month has now been closed. Seven people had fallen ill in the police K-9 unit cluster, which developed after a para-veterinarian contracted Covid-19.

As the cluster has not had new cases linked to it for 28 days, or two incubation periods, it is now closed.

MOH added that since Feb 5, newly arrived work permit and S Pass holders in the construction, marine and process sectors, and foreign domestic workers and confinement nannies who have recent travel history to higher-risk countries or regions have been progressively required to undergo mandatory on-arrival polymerase chain reaction and serology tests.

"These have enabled us to quickly identify persons who have recovered from an old Covid-19 infection, and are no longer infective to others by the time they arrived in Singapore, and to exclude them from our daily case count," it said.

There were no community cases or cases from migrant workers' dormitories. With 20 cases discharged yesterday, 59,646 patients have fully recovered from the disease.

A total of 30 patients remain in hospital, including one in the intensive care unit who is in critical condition. Another 90 are recuperating in community facilities.

Singapore has had 29 deaths from Covid-19 complications, while 15 who tested positive have died of other causes.