Soaring use of self-test kit sparks concerns over underreporting of COVID-19 cases

Medical workers carry out rapid antigen tests at a COVID-19 testing station in Seoul, Friday. Yonhap

By Bahk Eun-ji

Concerns are growing over whether rapid antigen tests will deal with the Omicron-fueled COVID-19 pandemic effectively, as they are feared to yield false-negative or false-positive results.

Since Thursday, the country has allowed only hospitals and medical clinics to conduct rapid antigen testing. Under the new system, only those who only test positive in a rapid test are able to receive polymerase chain reaction (PCR) tests. Prioritized for PCR tests are the elderly aged over 60, people who have come in close contact with a COVID-19 patient and those with a doctor's recommendation citing the need for the laboratory-processed test.

According to the Central Disaster and Safety Countermeasures Headquarters, Friday, a total of 84,000 rapid antigen tests were conducted using at-home test kits at testing centers in four local jurisdictions ― South Jeolla Province, Gwangju and the Gyeonggi Province cities of Pyeongtaek and Anseong.

Of them, in 687 rapid tests that came out positive, 164 of those, or 23.9 percent, came out negative in further PCR tests.

Experts say these false positives indicate the reduced accuracy of the rapid antigen tests.

These tests use a method of collecting a specimen from a place not deep inside the nose and putting it in a diagnostic kit to confirm whether or not the virus is detected within 30 minutes, taking much less time than a PCR test.

A more accurate PCR test is determined by amplifying the viral gene in a collected sample.

There is also a possibility of the rapid antigen tests producing false negative results. While it is possible to determine whether a sample is positive even with a small amount of specimen, a rapid test can possibly show negative results even for an infected person if their symptoms are mild or if the specimen was not collected properly.

According to a study by the Korean Society of Diagnostic Laboratory Medicine, only 41.5 percent of infected people tested positive on the rapid antigen tests, meaning that six out of 10 infected people could be wrongly told they don't have the virus.

If the general public directly uses the rapid antigen test kit, it can be 10 percent to 20 percent lower than that, and that means many people can spread the virus unwittingly, the organization said.

“If the rapid antigen test is negative, it is considered negative,” Son Young-rae, a senior health ministry official, said in a regular briefing, Thursday.

“This means that we take the risk of some false-negative results.”

Kim Woo-joo, a professor of infectious medicine at Korea University Guro Hospital, explained how a false-negative result occurs. “Because the rapid antigen test requires at least 1,000 times more virus than the PCR test to be positive, it cannot be detected in the early stages when the amount of virus is small,” he said.

“If a person who tested negative falsely through a rapid antigen test is allowed to use multiuse facilities for 24 hours under the vaccine pass system, they can be an unwitting virus spreader.”

Meanwhile, the country reported 27,443 new COVID-19 infections for Thursday, including 27,283 local cases, raising the total to 934,656, according to the Korea Disease Control and Prevention Agency (KDCA). The daily new infections have surged sharply in recent days, breaking the 20,000-mark for the first time Wednesday.

In order to contain the upward trend, the government decided to extend the current social distancing rules for two more weeks through Feb. 20, during which private gatherings of more than six people will be restricted and business operations are also subject to a 9 p.m. curfew.