The origin of Hong Kong’s first locally detected Covid-19 infection in more than 50 days continues to baffle officials, although researchers have found similarities with other Delta variant cases found recently in Britain.

Genome-sequencing testing on the 48-year-old airport worker confirmed as infected on Friday revealed a close resemblance to infections detected last month in the country, according to Polytechnic University analysis. But Dr Gilman Siu Kit-hang, of the university, said researchers were still unable to determine how he got infected.

The Environmental Protection Department, meanwhile, announced that sewage samples collected from Tai Wai’s Golden Lion Garden, where the cargo handler lives with his family, returned positive for the coronavirus.

“The viral load content of the sample is lower than normal, with a CT [cycle threshold] value of 35. It is currently uncertain whether the sewage sample carried any variant strain,” the department said. The lower the CT value, the higher the viral level.

Dr Gilman Siu Kit-hang, Polytechnic University’s associate professor of department of health, technology and informatics.

The department said it would arrange to take more sewage samples in the area once the harsh weather over the past two days brought on by Tropical Storm Lionrock had subsided.

Respiratory medicine expert Dr Leung Chi-chiu said the positive sewage samples in the area suggested the airport worker was probably the first coronavirus infection detected in Hong Kong of this particular type, known as an index case.

“If repeated samples are persistently positive after isolation of the index case, there will be a need to advance the next round of screening of residents to pick up any spread within the building,” Leung said.

Also on Saturday, Hong Kong confirmed eight new coronavirus cases, all imported. Three arrived from Pakistan, two from Indonesia, and the rest came from the Philippines, India and Nepal. The city’s tally now stands at 12,261 cases with 213 related deaths.

The latest community case, which on Friday ended Hong Kong’s 51-day run without a local infection, carried the L452R mutation which has been linked to several variants including the highly infectious Delta one.

The patient was tested regularly as a requirement of his cargo handling job at Hong Kong International Airport and received his second dose of Sinovac’s Covid-19 vaccine in July. Medical experts have said that while vaccines do not offer total protection against infection, they vastly reduce the severity of the illness and likelihood of death.

The infection is the first locally detected case since an airport lounge employee was confirmed with the coronavirus on August 17.

The wife and five-year-old daughter of the 48-year-old cargo handler have both tested negative. The family of three live in Golden Glory Court Phase 1 in Tai Wai’s Golden Lion Garden.

Testing of 400 residents in their building uncovered no new infections, while about 30 children from the daughter’s kindergarten were sent into mandatory quarantine for three days.

Meanwhile, the turbulent weather that triggered rainstorm and typhoon warnings in Hong Kong forced the suspension of Covid-19 vaccination and testing centres on Saturday, after disrupting services the day before.

Those whose vaccination bookings were affected would receive an SMS notification to reschedule their appointment.