Health officials, meanwhile, revealed that between 70 and 80 security guards at the Harbourfront Horizon Suites hotel in Hung Hom had been quarantined, after at least five of them tested positive for Covid-19.

“Some of the guards tested positive at the quarantine centre. We earlier had sent those who shared changing rooms to isolation,” Dr Chuang Shuk-kwan, head of the communicable disease branch of the Centre for Health Protection (CHP), said.

The city confirmed 60 new coronavirus infections and close to 40 preliminary-positive cases.

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First 3D scan of the real coronavirus revealed

First 3D scan of the real coronavirus revealed

Professor Yuen Kwok-yung, who inspected Block C of the Tung Fat Building in the afternoon, said he suspected vertical transmission was happening among flats numbered 6 and 7.

“We would recommend evacuation of these households and mandatory testing for all residents living in the same block,” Yuen, a top government pandemic adviser, said.

Block C has had 13 infections, including five preliminary-positive cases, in eight flats.

According to officers involved in the inspection, flats numbered 5 to 8 share a common air shaft, where waste water and sewage from kitchens and bathrooms discharge, and the chimney effect occurred.

Dr Albert Au Ka-wing, principal medical and health officer at the CHP’s communicable disease branch, said seven of the eight flats faced the same direction. Five were in flats 6 and 7.

“From the onset dates of the cases, we suspect there could be vertical transmission in C6 and C7 units,” Au said.

Officers from the environmental protection and buildings departments found the block was in satisfactory condition. The building was completed in 1965 and renovated about seven years ago.

Carrie Lam defends surprise lockdown in face of residents’ complaints

“The drains don’t seem to be leaking and there are U-bends installed,” Kenneth Leung Kai-ming, principal environmental protection officer, said.

“But the design of the building is such that two units face the same lightwell, which is enclosed and [infected aerosols could go up through it as] the ventilators installed in kitchens and toilets do draw air out into the lightwell.

“Therefore, we suspect there could be a possibility of the ‘chimney effect’ having taken place.”

Yuen said he had heard from residents that there were subdivided units in seven to eight flats.

Block C was issued a compulsory testing notice on Monday for anyone who had visited the building for more than two hours between January 12 and 25, with residents required to get tested by Thursday. The block has about 400 residents, and 217 had taken a test, according to Yuen.

He also said a lockdown order in the area could not be ruled out if the number of cases increased.

Of the latest cases citywide, 57 were local infections while the other three were imported. Twenty-one local cases did not have a clear source of infection. Four cases were from Yau Ma Tei district, which was recently hit by an outbreak.

Another two people, both chronically ill, died after contracting Covid-19. A 67-year-old man succumbed in the morning, while a 56-year-old woman, who tested preliminary-positive, died on Tuesday afternoon.

The tally of confirmed cases stood at 10,282, with 174 related deaths.

Twenty more buildings were to be issued with mandatory testing orders. They included six blocks where cases were found in two unrelated flats. The others were three buildings from the specified areas of Yau Tsim Mong district where one infection triggers testing, and 11 blocks in Hung Hom where sewage samples have consistently tested positive for the virus.

Chuang also appealed to those who had visited a Hung Hom congee shop called “Wing Ming”, where six staff members were confirmed infected and another worker tested preliminary-positive, to get tested.

She said four of the six confirmed cases were from the same family, suggesting transmission within the cluster.

“So far, no members of the public have been confirmed with Covid-19 after visiting the congee shop. If anyone had been to that shop between January 16 and 23, please get tested as soon as possible,” Chuang said, noting that the outlet had already been asked to close after the first case emerged.

A resident from Kin Ling Elderly Home in Jordan was also among the confirmed infections on Wednesday. Another person from the home was a suspected case.

Separately, the Housing Authority started drainage inspection and repair works early this month for 34 public housing blocks that had been subject to mandatory testing, according to a written reply to lawmakers from Secretary for Transport and Housing Frank Chan Fan on Wednesday. The work was expected to be completed by Saturday.