Hong Kong police were hunting a 25-year-old woman who fled from compulsory quarantine, the second coronavirus-related escape in less than a week, as 53 new Covid-19 cases were confirmed on Wednesday.

The latest caseload, the lowest since the fourth wave of infections broke out about a month ago, included 47 locally transmitted infections, of which 20 were untraceable. The remaining six were imported. More than 40 preliminary-positive cases were also recorded.

The tally of confirmed infections stands at 8,353. The city also recorded its 133rd coronavirus-related death – a 77-year-old chronically ill man tied to a cluster involving dancing venues.

Dr Lau Ka-hin, the Hospital Authority’s chief manager for quality and standards, said the woman, who tested negative for the virus and was quarantined at a facility in Penny’s Bay on Lantau Island as a close contact of a patient, told health officers she had a chest problem and was sent to North Lantau Hospital on Wednesday for checks.

“But she did not take the vehicle arranged by the Department of Health to return to the quarantine centre and left on her own,” Lau said. “If residents are under quarantine or isolation after being confirmed with the virus, it’s irresponsible when they run away.”

Her disappearance came just days after officers tracked down a patient who had escaped from a public hospital last Friday.

Lau said the authority had reminded hospitals to pay extra attention to patients under quarantine and step up security measures if necessary.

The hospital reported the case to police, who called the woman’s smartphone.

“She answered the call but refused to return to quarantine,” a police source said. “She did not pick up the phone afterwards and we are arranging colleagues to try to find the woman at her home.”

Meanwhile, Dr Chuang Shuk-kwan, head of the Centre for Health Protection’s communicable disease branch, said lab workers, analysing 11 infections, had found the genetic sequencing of two imported cases appeared to match a new virus variant that British health authorities warned was spreading out of control across London and southeast England.

A check by University of Hong Kong experts confirmed the sequencing found in the two cases was in line with the variant.

“We initially know that two people may be linked to the new virus variant,” Chuang said.

“We have to do more analysis. This, perhaps, is expected because it was reported that Britain had a relatively large proportion of people carrying such a virus. So imported cases in Hong Kong should have a certain percentage of that.”

She said close contacts of one patient would be sent back to quarantine for seven more days.

One student returned to Hong Kong on Cathay Pacific flight 252 on December 7, and the other on Virgin Atlantic flight 206 on December 13. One has recovered and left hospital.

Chuang also warned that even though the number of infections in Hong Kong had dropped, the percentage of untraceable cases was quite high.

“Each of these cases, regardless of traceable or untraceable, can trigger some clusters to emerge or even some outbreaks, so everyone should be careful,” she said.

Lau said a female patient, 91, tested preliminary-positive for the virus, as did two others who had been in the same ward at United Christian Hospital in Kwun Tong.

She had been admitted due to a terminal illness but was discharged on Monday. But when a community nurse visited her at home the next day, she was suffered from a slight shortness of breath. After a check at the hospital, her initial test result returned positive.

Lau said the patients were in a palliative care ward so family members seemed to have visited them on compassionate grounds.

Health authorities would investigate whether their infections were linked to the visits.

“After this, this ward will not allow visits on compassionate grounds,” he said.

“For [other wards] we will let experts look at the visit arrangements. We are still not sure what is the source of infection.”

More residents tested positive at Ping Shing House in Lam Tin’s Ping Tin Estate, taking the number of flats affected there to five, involving eight cases. A few preliminary-positive cases were reported. Authorities issued a mandatory testing order for the block.

Specimen bottles were also given out to residents of Block 4 at Hong Sing Garden in Tseung Kwan O after five people from three flats contracted the virus.

One of the flats housed a worker from Fong Shu Chuen Day Activity Centre and Hostel, a facility in Shau Kei Wan for the intellectually disabled, where a cluster was reported. Patients living in two other flats were infected by unknown sources.

The Hospital Authority would arrange 11 general outpatient clinics during the Christmas holidays for residents to collect and return specimen bottles.

In Hong Kong, it is illegal for anyone who is in quarantine at a government facility or in isolation in hospital to leave without official permission. The offence is punishable by a fine of HK$5,000 (US$645) and up to two months’ imprisonment.