A fully vaccinated woman who was working as a cleaner at a community care facility in Tuas South was the sole unlinked case out of the 16 community cases announced by the Ministry of Health (MOH) on Thursday (April 29).
The 39-year-old Vietnamese national dons full personal protective equipment while at work - including an N95 mask, face shield, gown and gloves.
She also periodically helps out at a food stall at The Summit located at the National University of Singapore's Bukit Timah campus.
She received her first dose of the Covid-19 vaccine on Jan 27, and the second dose on Feb 19.
MOH said that while the Covid-19 vaccine is effective in preventing symptomatic disease for the vast majority of those vaccinated, it is possible for vaccinated individuals to get infected.
The woman had been asymptomatic, but her case was picked up when she was tested on Monday as part of rostered routine testing, MOH said.
Her pooled test result came back positive for Covid-19 the next day, and she was taken by ambulance to the National Centre for Infectious Diseases.
An individual test was done on Tuesday and her test result came back positive for Covid-19 infection.
Her earlier tests from the routine screening - the last being on April 14 - were all negative for Covid-19 infection, the ministry added.
The other 15 community cases announced by MOH on Thursday were linked to existing clusters.
Eight of them - two staff and six patients - were linked to the nurse at Tan Tock Seng Hospital (TTSH) who was working at Ward 9D, a general ward.
These cases had mainly been detected by MOH's proactive testing of patients and staff in the affected ward.
Measures have been put in place at the hospital to prevent further transmission, including barring visitors from entering the hospital except for critically ill patients.
The other seven community cases were family members of a prior Covid-19 case - a 38-year-old Immigration and Checkpoints Authority officer - that MOH had announced on Wednesday.
The ministry said that the man and his family had gathered for a meal on Sunday, when the transmission was likely to have taken place.
MOH also reported 19 imported cases on Thursday, including two Singaporeans and nine permanent residents.
There are also three dependant's pass holders and five work permit holders, including a foreign domestic worker.
All had been placed on stay-home notice upon arrival in Singapore and were tested while serving it.
There are currently 110 confirmed cases who are still in hospital. Of these, most are stable or improving, and none is in the intensive care unit.