Chuang Shuk-kwan, with Lau Ka-hin, says there were four imported cases.

A 37-year-old woman has tested positive for Covid-19 again, three days after she was discharged from hospital, in the second such case in three days.

The woman complained of breathing difficulties and chest discomfort on Tuesday and was readmitted to the Alice Ho Miu Ling Nethersole Hospital in Tai Po.

Hospital Authority's chief manager for quality and standards Lau Ka-hin said doctors tested her again and found her to still be positive but with a low viral load.

"She is now in a stable condition and staying at the hospital for treatment of her symptoms and more tests to monitor her situation," he said, adding that the 37-year-old was unlikely to be infectious.

The Centre for Health Protection's head of communicable disease branch Chuang Shuk-kwan said the woman did not go home after being discharged but stayed in a Tsim Sha Tsui hotel before being readmitted to hospital.

The woman previously stayed at The Imperial Hotel Hong Kong and Prudential Hotel in Tsim Sha Tsui for her 14-day quarantine after returning from traveling in Sweden and Finland on April 2.

She eventually developed a mild sore throat and was diagnosed with Covid-19 on April 8.

Lau said: "During her first stay at the hospital, she did not suffer from a fever or any other symptoms, so we did not use any anti-viral drugs on her."

On Monday, a 17-year-old youth tested "weak positive" after he was discharged from hospital on April 7.

The teen, who studies in Britain, returned on March 22 and was diagnosed five days later.

Yesterday, Hong Kong confirmed four imported cases from Britain - two women aged 26 and 52, a 68-year-old man and a two-year-old boy - taking the tally to 1,036 with deaths remaining at four.

The toddler was in the UK with his mother between February 4 and April 12.

Chuang said the mother tested negative, but she and her husband, who live with the baby at Louver Mansion in Fan Ling, will be sent to quarantine centers.

Meanwhile, a 24-year-old medical student at the University of Hong Kong developed a low fever before an exam on Tuesday.

He was refused entry to the exam venue at Hong Kong Academy of Medicine in Wong Chuk Hang and went to a private hospital, where he tested "preliminary positive" for the coronavirus.

However, subsequent tests came back negative, Chuang said, adding it could be a "fake positive" result.

Authorities will continue to monitor the student's health, with his family and close friends now under medical surveillance.

Separately, the Airport Authority announced that an outbound passenger who was later diagnosed with Covid-19 in Japan had visited its lounge near gate one at the Hong Kong airport's restricted area Monday. The authority has closed the lounge for sanitization.