Coronavirus: sample contamination at Hong Kong Covid-19 testing lab could explain high number of positive results in single day, expert says

Elizabeth Cheung
·9-min read

Sample contamination at a Covid-19 testing lab could explain an unusually high number of preliminary-positive cases detected in one day, an expert investigation has found, presenting another challenge on Hong Kong’s path to containing a resurgence of infections.

University of Hong Kong microbiologist Professor Yuen Kwok-yung revealed his findings after an inspection of testing firm BGI’s facility on Thursday evening, after the company earlier reported 30 preliminary-positive cases in a day.

It is not the first time the mainland-backed contractor has been embroiled in controversy over tests. But it was not immediately known whether the lab had violated any protocols in the incident.

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Earlier in the day, health officials also revealed around 30 kindergarten pupils would be quarantined after their teacher was confirmed as one of two local Covid-19 cases. The city also recorded 12 new imported cases.

Dr Albert Au Ka-wing of the Centre for Health Protection (CHP) said it was “a bit unusual” that 30 positive cases were detected by a single lab on the same day. As a precaution, health authorities would treat them like confirmed cases and send the patients’ close contacts to quarantine centres.

They also recommended schools and workplaces of those who tested positive to temporarily close and for people to undergo testing.

“If these are true positive cases then there is silent transmission or even outbreaks in the community which have not been detected before,” Au warned at a regular Covid-19 briefing.

Professor Yuen Kwok-yung. Photo: SCMP Pictures
Professor Yuen Kwok-yung. Photo: SCMP Pictures

Shortly after Au spoke, Yuen visited the BGI lab in Tai Po and said that of the 30 cases, at least two were confirmed to be positive after further testing.

Coronavirus from these two positive sample bottles was believed to have spread accidentally to the 28 others that lab workers were handling, he said.

Dr Ambrose Wong from the CHP added that 10 people tested negative upon hospital admission. Results for the remaining 18 were pending.

Each bottle contained a detergent-like solution used to kill the virus, Yuen said. After a bottle was opened, the solution formed bubbles which could burst and contaminate the worker’s gloves. “There could be cross-infection this way,” Yuen said.

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In the lab, plastic trays held about 100 samples for testing and they would be used for one batch after another. If a tray was contaminated, it could spread the virus to other samples, Yuen said.

Another problem, he noted, was that each worker was responsible for testing 800 samples every day.

“They could be fatigued and thus their awareness to change their gloves could be lowered. Their workload should be redistributed,” he said.

Yuen asked the lab to improve its work flow, including that the workers change their gloves frequently and that plastic trays should not be reused.

Au noted all 30 preliminary-positive patients had been sent to public hospitals for isolation as a precaution.

Nine of the 30 cases involved people at the Ramada Hong Kong Grand, a designated quarantine hotel in Tsim Sha Tsui. The property had been issued with a mandatory testing order after it was linked to the city’s first locally detected case of a mutated virus strain.

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The other 21 cases came from four community testing centres and from districts including Tuen Mun, Wong Tai Sin and Tsz Wan Shan, and no cluster patterns were seen. They included people who are required to undergo regular testing, such as construction workers and cleaners.

The latest incident is at least the third involving BGI. Police arrested a BGI lab assistant after he was accused of tampering with Covid-19 test specimens. Authorities revealed that 16 samples processed around late January to early February returned “false positive” results. Further testing confirmed they were negative.

BGI’s lab is in Tai Po. Photo: SCMP Pictures
BGI’s lab is in Tai Po. Photo: SCMP Pictures

Last month the government issued a warning letter to the company after it was unable to notify people of their negative test results, involving 2,800 specimens submitted for testing between late February and early March.

Asked how the incident would be handled if procedural problems were found, Undersecretary for Food and Health Dr Chui Tak-yi said: “The government will monitor the performance of companies carrying out outsourced work. In principle, if they do not reach the contract standard or what is required from them, then authorities will take decisive action, which may include termination of the contract.”

In a statement late on Thursday evening, the government revealed BGI was also involved in three positive results which later came up negative in follow-up hospital tests. The samples were taken from a kindergarten teacher and two people who travelled to mainland China.

It added the Department of Health would investigate the operations of BGI laboratories and testing centres.

Alex Li Wai-chun, chairman of the Hong Kong Association of Medical Laboratories, suggested the testing outcomes from BGI were not in line with the local epidemic situation.

“If dozens of specimens were obtained from different places and tested positive at the same time, it seems not in proportion to the current infection rate in Hong Kong,” Li said.

He said the authorities should look into whether the firm kept making the same mistakes. “The government should not take it lightly and find out the reasons behind the problem,” he said.

Thursday’s two local infections were both untraceable, while eight imported cases arrived from India, two from Nepal, and one each from Turkey and Pakistan. Four of the imported infections carried the N501Y mutation, taking the total of variant-strain cases identified in Hong Kong to 235.

The city’s tally of confirmed cases stood at 11,718 cases, with 209 related deaths.

The 31-year-old female teacher worked at the Lohas Park campus of Greenfield English (International) Kindergarten and had taught two classes of K3 pupils for around 15 to 30 minutes on Tuesday, the most recent day she was in school.

“Both the teacher and the pupils wore masks. But since the learning environment was enclosed and the teacher was in the onset period, which could be more infectious, about 30 pupils in the two classes and two teaching staff will be quarantined,” Au said.

Children were normally accompanied by a guardian at a quarantine camp while those without one would be sent to an isolation facility for children at Lei Yue Mun Park and Holiday Village in Chai Wan, he added.

Au said the woman had visited multiple places during her incubation period, including a friend’s home and a gym in Hang Hau, two restaurants in Tin Hau and Causeway Bay, a wedding expo at the Hong Kong Convention and Exhibition Centre in Wan Chai, and a venue in Kwun Tong for a yoga class.

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The other untraceable case was a 19-year-old man employed at Kwai Tsing Container Terminals. He worked as a checker under the company Wang Kee at piers 1, 2 and 5 of the terminal.

“He didn’t contact cargo workers at the piers. He also didn’t need to go up to ships. His main duty is inputting data of newly arrived cargoes on computer,” Au said.

Meanwhile, two scientific committees under the Centre for Health Protection suggested shortening the quarantine period from 14 days to seven for close contacts who had received their second dose of vaccines for at least two weeks and tested negative.

The committees also sought to clear the public’s doubts over pregnant women taking vaccines, saying more than 90,000 had already been vaccinated globally with no major risks detected. One woman in Hong Kong suffered a miscarriage and another experienced a fetal death after receiving BioNTech jabs but an expert panel concluded on Wednesday that there was no evidence indicating an association.

In other news, the first of two designated flights bringing residents back to Hong Kong from Britain arrived from London on Thursday morning carrying 291 passengers. All tested negative for the virus at Hong Kong International Airport. They will undergo 21 days of quarantine at the Rambler Garden Hotel in Tsing Yi and will be tested on the 7th, 12th, 19th and 26th day of their stay.

More than 1 million Hongkongers aged 16 to 29 will be able to make a booking for Covid-19 vaccines starting from 9am on Friday. The expansion of the scheme means that 6.5 million people in the city are eligible for the shots.

The children will be sent to a quarantine centre. Photo: Dickson Lee
The children will be sent to a quarantine centre. Photo: Dickson Lee

Local tours could resume as early as May 8 after the industry struck a deal with the government that no longer required sightseers to get vaccinated against the coronavirus, according to the city’s tourism lawmaker Yiu Si-wing.

Those joining tours – banned in Hong Kong since the fourth wave of infections hit last November – would have to use the government’s risk-exposure app but would not be made to sign up for Covid-19 jabs, Yiu told a radio programme.

Yiu revealed the government had “reached a consensus” with industry representatives, and was likely to table proposals for reopening local tours when the Executive Council next met on Tuesday.

Those embarking on the tours would have to document their visits to various premises on the “Leave Home Safe” app, through which users are notified if a Covid-19 patient has been to any of those places in a certain period.

But Dr Leung Chi-chiu, a respiratory medicine specialist, told the same show the city had to proceed cautiously with any plans to relax social-distancing restrictions, given the confirmation of cases involving mutated strains.

Separately, Simon Siu Yat-ming, chairman of the Hong Kong Registered Specialist Contractors (Ventilation) Association, said only 4,000 to 5,000 restaurants – from a total of more than 10,000 in the city – would meet the April 30 deadline for upgrading their ventilation facilities to provide indoor air changes six times per hour. He said many had encountered difficulties procuring purifiers at a price they could afford.

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