Are you absolutely positive?

BGI in Swedish row over how Covid test results are interpreted


Brunei, an oil-rich sultanate in Southeast Asia, seems to have contained the coronavirus outbreak pretty effectively. As of September 7, the local infection rate was one of the lowest worldwide. Health authorities attribute some of their success to the adoption of RT-PCR, a nucleic acid-based testing method that identifies virus carriers. Unlike more traditional blood screens the RT-PCR technique doesn’t target antibodies, which take days to form. Moreover, the test yields results quickly, within three hours.

Following its first confirmed case in early March Brunei established a ‘Fire Eye’ laboratory of nucleic acid extractors capable of processing thousands of tests a day. The provider of the technology is BGI Group, the Shenzhen-based genome sequencer. By the end of June BGI had sold 35 million Covid-19 test kits and built 58 Fire Eye labs in 18 countries.

This new demand – which helped push BGI’s net profits up seven times to Rmb1.7 billion ($247.2 million) in the first half – was in part due to aggressive promotion by China’s embassies in an extension of what is being dubbed the country’s “virus diplomacy” (see WiC488).

But as BGI’s test kits have become more widely available, the company has also been attracting less welcome attention.

Last month Sweden’s public health agency complained that BGI’s test kits had yielded 3,700 false positive results due to an apparent inability to distinguish between very low levels of the virus and negative results. “The supplier must adjust the performance that is required for this test to be used,” the head of the agency’s microbiology department said.

BGI defended itself by saying that its testing procedures had “relatively high accuracy” and some of the problems relate to the varying standards that countries adhere to in assessing viral load.

“Different countries and regions define asymptomatic patients differently,” it said in a statement, noting that countries like China adopt a lower viral load threshold when assessing whether Covid-19 is present.

In an interview with the Global Times, BGI suggested that Sweden prefers test results generated with low-sensitivity reagents as opposed to high-sensitivity ones, despite the risk that asymptomatic virus carriers can return ‘negative’ results.

Indeed, in its complaints about BGI, the Swedish health department acknowledged that “it is mainly people who have had mild symptoms or have not felt any symptoms at the time of the test who have received false positive answers.”

The statement led the Global Times to criticise Sweden’s government for suffering from “a clear logic fallacy” and likewise for the country’s ‘passing the buck’ to BGI to divert domestic attention from its own failures in containing the virus.

The Nordic country recorded its highest death tally in 150 years during the first six months of 2020, according to CNN.

BGI’s test is underpinned by next-generation genome sequencing. It works by converting genetic material from the nose and throat into complementary DNA, which is then amplified to check whether it binds to the SARS-Cov-2 genome. If it does, a fluorescent dye is released. When a specified level of fluorescence is surpassed this provides the confirmation that the virus is present.

“When you have many cases, this kit is very good. It will not miss any positive cases. This means that you can rely on the results, but you also have a chance to get a ‘false positive’,” the head of the Swedish microbiology unit acknowledged in a BGI press release dated September 4.

“But when the situation changes, and you have a very low number of infected individuals in society, as we have now, then you can lower the sensitivity and be sure that you pick up the right positive cases so you have not so many false positive cases. This is the situation now and we have now changed the threshold or the sensitivity of the test, so now it works perfectly fine in Sweden. We can rely on the test today,” he clarified.

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