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‘US agency's COVID-19 test based on easily mutated gene’
  • By Song Soo-youn
  • Published 2020.03.19 17:13
  • Updated 2020.03.26 12:02
  • comments 0

Skeptics say that Korean testing for the new coronavirus (COVID-19) might be inaccurate, but most of their claims are wrong, local experts say.

Earlier, a U.S. Republican congressman claimed that urgent test kits in Korea were less reliable than those in the U.S. However, he was referring to antibody testing, not used in Korea, the experts note.

Recently, some U.S. critics raised concerns that Korean test kits target different genes from those used by the U.S. Centers for Disease Control and Prevention (CDC), saying Korean testing is less sensitive. The CDC looks at the N gene when detecting COVID-19, but the Korean authorities do not, which leads to lower sensitivity, these critics said.

Again, however, such an assertion was inaccurate, the Korean experts noted.

Lee Hyuk-min, director of infection control affairs at the Korean Society for Laboratory Medicine, pointed out that the N gene can get highly mutated, at a YouTube show Tuesday by K-Healthlog, a channel operated by The Korea Doctors’ Weekly.

“It is unlikely that the specificity and sensitivity increase by the gene targeted by the diagnostic reagent. Determining them is the composition of diagnostic reagents,” Lee said. “Korea uses a molecular diagnosis developed in Germany, which is also used by the World Health Organization. The Korean method includes the E gene and the RdRP gene only.”

Korean molecular diagnostic tests exclude the N gene because it can get mutated severely, he added.

‘US tests on N gene not more sensitive than Korean tests’

According to Lee, the N gene encodes a nucleocapsid, a site that is highly mutated due to its structural properties. For this reason, targeting the N gene could fail to detect COVID-19 if the N gene was mutated, he noted.

After analyzing the entire gene sequence of the COVID-19 virus, Lee found that there were too many mutations of the N gene.

Based on this, Lee said it would be better to put the E gene and RdRP gene mainly and a little bit of the N gene for a complementary role, in the diagnostic reagent.

“That is why we chose WHO-recommended testing primarily,” he said.

Some researchers suggested excluding the E gene and putting the N gene and RdRP gene only, Lee went on to say. The test on the E gene seems more sensitive than that on the N gene, he said.

“In terms of specificity, the RdRP gene has the highest. So, France looks at the RdRP gene only, when testing COVID-19,” he said.

Correction from negative to positive may be due to viral properties

Some people test negative for COVID-19 in the initial detection but later turn positive probably because of the patient’s status or properties of the virus, according to Lee.

“Korean physicians use Kaletra (an HIV drug) to hospitalized COVID-19 patients a lot. So, the virus could be suppressed by the drug, not by the patient’s immunity. If the drug’s effect fades, the virus could be in reactivation,” he said.

COVID-19 seems to have mutations a lot, and many studies reported cases of patients testing initially negative but turning positive later, he said.

One local tertiary hospital saw a clear negative outcome from bronchoalveolar lavage (BAL) fluid, one of the best samples for detecting a respiratory virus. The following day, however, the hospital could find the virus in the upper respiratory tract, Lee said.

“In China with the largest number of clinical cases of COVID-19, even if a person tests negative twice and gets lifted from quarantine, the person is advised to get tested again in the second week and fourth week. This is because they worry about the reactivation of the virus,” he said.

Six diagnostics societies in Korea released a statement, saying the U.S. has diagnostic reagents that do not detect the N gene, and that China, Germany, and France were also using other genes for COVID-19 testing.

The Korean authorities reviewed diagnostic agents targeting not only the E and RdRP genes but additional genes (N gene, ORF1a gene) and approved them for urgent use, they said.


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