Freak infection linked to inhaled DNA fragments

Top News | 18 May 2021

Jane Cheung

A worker at a mainland-run laboratory in Tai Po carrying out tests could have inhaled noninfectious DNA fragments of Covid-19 during an overnight stay and then tested positive for the virus the next day.

Expert Yuen Kwok-yung presented that scenario to explain a freak case. The 29-year-old man, fully vaccinated, had shown up as a coronavirus case at first but then tested negative after being admitted to hospital on May 7. Then it became apparent he had no symptoms of Covid-19 at all, which led to him being given an all clear.

Speaking after inspecting the Shenzhen-headquartered BGI laboratory in Tai Po Industrial Estate yesterday, University of Hong Kong microbiologist Yuen said the lab conducts tests on the coronavirus' DNA fragments and the room used for that is adjacent to the lounge. So the DNA could have drifted between rooms.

He said the DNA fragments are not contagious but they can lodge in a person's nose and throat for a time. "It's likely the staff had not worn his mask properly when he rested and inhaled the DNA in the air," Yuen said.

The man, who had his second shot of the German-made BioNTech/Fosun vaccine on April 10, was classified as having an untraceable local infection on May 7 after being tested at a Yuen Long mobile station three days earlier.

But genetic sequencing found his infection had not been caused by mutant variants in the SAR and authorities eventually cleared him on Saturday.

Yuen said: "This is a bizarre incident. But it should be an isolated event." He suggested labs use ultraviolet lighting to disinfect places when they are not in use.

Another unknown-source local infection is a four-year-old boy at HKVNS Alumni Association Kindergarten (KCC) in Ho Man Tin.

The boy, whose infection was announced on Saturday, tested negative for the coronavirus and antibodies after he was admitted to hospital, prompting experts to speculate he was a "false positive" case.

Yuen said it may take the immune system seven days to develop antibodies after contracting Covid-19 and it was too early to conclude the boy was a false positive case.

Hong Kong yesterday reported only one imported case - a 25-year-old helper from Indonesia - to take its tally to 11,826, including 210 deaths.

Yuen said the SAR is hopeful of seeing zero infections soon, but he is worried that will result in people thinking there is no urgent need to get vaccinated.

But if the SAR suffers a rebound, he warned, there could be as many as 1.5 million cases, with 20 percent of the 7.5 million population infected within a short time. And 15,000 people could die amid a sudden surge.

He noted too that the BioNTech vaccine stocks expire in September and called upon people to get the jab.

As of Sunday, 1.17 million people have had at least one shot, including 505,400 with the Beijing-made CoronaVac from Sinovac and 662,500 with BioNTech's Comirnaty. Among them 787,200 have completed both doses.

The uptake rate is 18 percent among 6.5 million people above 16.

Authorities reported one more post-inoculation death - a 50-year-old man admitted to North Lantau Hospital on Sunday who passed away the same day, 13 days after his second Sinovac jab.

Experts said the provisional cause of death was a stroke and the death was not related to the vaccine. So far, 34 post-inoculation deaths have been reported, including 24 taking Sinovac and 10 BioNTech.

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