Patients who have non-emergency surgery within six weeks after diagnosis for Covid-19 are over 2 times more likely to die after their operations, the researchers said.

The university said yesterday that 45 CUHK doctors have joined with more than 15,000 surgeons worldwide to find out the optimal surgery time for Covid-19 patients.

The research team collected data from 140,727 patients in 1,674 hospitals across 116 countries and found that patients operated on within six weeks after diagnosis and with Covid-19 symptoms at the time of surgery face higher risks of death.

About 4 percent of Covid-19 patients who had surgery within four weeks after infection died, the study found. But if patients had surgery after seven weeks, the mortality rate would drop to 1.5 percent - the same as patients who were not infected with Covid-19.

An assistant professor in CUHK's department of surgery, Kaori Futaba, said half of Covid-19 patients developed pulmonary complications after operations, which could lead to a high mortality rate.

"International guidelines therefore recommend surgery be delayed for patients testing positive for Covid-19. However, the optimal duration for delays was unknown. This study has shown that surgery should be delayed by seven weeks, if possible," she said.

But Futaba also reminded doctors to balance the potential advantages of the surgery delay against the clinical urgency of patients' condition.

CUHK medicine professor Simon Ng Siu-man said: "There are over 11,000 confirmed Covid-19 cases to date in Hong Kong. Some of these patients may now require elective surgery.

"We have a patient under our care in Prince of Wales Hospital with rectal cancer, who had Covid-19. This data has allowed us to optimize the timing of the surgery in order to minimize Covid-19 related peri-operative risks," he said.

Meanwhile, a male Covid-19 patient died in Queen Elizabeth Hospital as the city recorded 12 new cases yesterday, including four local cases and eight imported cases from France, Pakistan, the Philippines and Indonesia, taking the tally to 11,410, with 204 deaths.

One of the local cases was untraceable and involved an 88-year-old man living in Ping Sin House at Ping Tin Estate in Lam Tin. He developed a fever on March 17 and was sent to the United Christian Hospital on Monday.

The other three local cases were related to the Ursus Fitness gym cluster, including a 33-year-old male customer of the gym and two close contacts of previous cases, aged 38 and 51.

Government adviser Yuen Kwok-yung said after visiting the Ursus Fitness gym on Monday that the outbreak was caused by the lack of fresh air exchange inside the gym.

Yuen said the fresh air flow in gyms should at least be the same as that of restaurants, with six air changes per hour.

The Covid-19 patient who died yesterday was an 89-year-old with chronic diseases. He was sent to Queen Elizabeth Hospital on January 5 due to cough, running nose and poor appetite.

The authorities said his condition continued to deteriorate and he eventually passed away at 1.30pm yesterday.