‘Lab contamination may have caused false positives’


  • 'Lab contamination may have caused false positives'

A prominent microbiologist on Thursday said he suspects cross-contamination in a private laboratory testing samples for the coronavirus may have resulted in more than two dozen false positives.

Professor Yuen Kwok-yung of the University of Hong Kong told reporters after inspecting a laboratory run by BGI in Tai Po that it appears that staff may have accidentally transferred the virus from two genuinely positive samples, to 28 others tested in the same batch.

The government had earlier asked him to look into any ‘irregularities’ after reporting 30 preliminary positive cases from a single lab on the same day.

“This appears to be very unusual because all of these patients have no epidemiological link, and many live in different districts, from Ngau Tau Kok to Tsuen Wan, so we had a suspicion that these may be false positives,” Yuen said.

Only two of the 30 ‘positives’ were later confirmed by separate tests run by the Hospital Authority, though officials were still following up on some of the cases.

Yuen posited that the virus may have been spread as workers opened vials of samples, contaminating their gloves or other equipment.

He recommended the lab to conduct a thorough disinfection, adding that all used gloves and vial containers should be changed for each batch.

The expert also noted that each member of staff handled some 800 samples per day, and the heavy workload may have caused fatigue and lowered their vigilance.

“We feel that handling so many samples every day is too tough for staff. Perhaps there’s a need to lower their workload and come up with a better distribution of work,” Yuen said.

The Centre for Health Protection (CHP) had earlier reported two new confirmed local cases of Covid-19, with neither of them having a clear source of infection.

One of them involves a teacher who lives in Tseung Kwan O, and works at Greenfield English International Kindergarten in Lohas Park. Around 30 children she taught have been sent into quarantine.

The other local case involves a 19-year-old man, who lives in San Wai Court in Tuen Mun, and works at the Kwai Tsing Container Terminals.

People who had worked with him were ordered to get tested.

Twelve imported cases were recorded, comprising people flying in from Nepal, India, Pakistan and Turkey – four of them were found to be carrying the N501Y mutation of the virus.

One of them was identified when being quarantined at the Ramada Hong Kong Grand Hotel in Tsim Sha Tsui.

Authorities suspect there might have been cross-infection between guests who were quarantined on the same floor of the hotel..

Officials said they had also ordered two more rounds of mandatory testing for people who’ve been to places where two patients carrying a highly infectious variant of Covid-19 visited – including Harbour City in Tsim Sha Tsui.