A growing number of novel coronavirus patients who have tested positive after recovery are keeping South Korea on its toes, despite the country reporting fewer than 40 new cases for the sixth straight day on Tuesday.

At least 124 patients who were thought to be cleared of COVID-19 had tested positive again as of Tuesday, with the number of recurring cases having more than doubled from 51 on April 6, according to the Korea Centers for Disease Control and Prevention.

Korea had a total of 10,564 cases as of Tuesday, up 27 from the previous day.

Health authorities said they were conducting tests to identify the cause, though they cautiously dismissed the possibility of patients being reinfected with the virus.

“We plan to divide and incubate the virus and analyze genes,” KCDC Deputy Director Kwon Jun-wook said during a daily briefing Tuesday. “We are closely looking into whether there are mutations in the important part (of the virus), which is critical in developing treatment and vaccines.”

The phenomenon probably stems from the patients’ weakened immune systems or from the reactivation of the virus, which may remain in the human body at undetectable levels, according to the authorities. There is also the possibility that the test results were in error.

Since Feb. 27, when the country saw its first case of a recovered patient testing positive again, the number of such cases has continued to increase -- from 51 on April 6 to 91 on Friday, 116 on Monday and 124 on Tuesday.

Recurring positive test results were reported in all age groups, though the greatest proportion, 22.6 percent, were in their 20s. This appears to be partially because this age group accounts for the largest portion of the country’s total cases at 27.32 percent.

Of the recurring cases, 18.5 percent were in their 50s, 15.3 percent in their 30s and 12.1 percent in their 60s.

The authorities are drawing up new measures to prevent apparently recovered patients from spreading the virus -- such as recommending self-isolation for two weeks even after being released from quarantine.

As of Monday, there were no cases of secondary transmission from recovered patients testing positive again.

World Health Organization also said Monday that not all people who recover from the coronavirus have the antibodies to fight off a second infection, raising concerns that patients may not develop immunity even after surviving the virus.

Korea, which once had the largest outbreak outside China, has seen a slowing trend in new infections in the past few weeks, with the daily infection tally staying in the double-digit range for the 13th straight day on Wednesday. This is a sharp drop from the peak of 909 new cases on Feb. 29.

Of all patients, 7,534 people, or 71.3 percent, have recovered.

The government, however, is on alert due to the continued influx of new infections from overseas and small-scale, sporadic outbreaks in the country. Of the country’s total cases, 940 have come from overseas, with 91.7 percent involving Korean nationals.

Of the new cases reported Tuesday, 12 came from overseas. Seven of those were detected at airport checkpoints and the rest after they entered the country.

By region, Gyeonggi Province saw the most new cases at eight. Five new cases were reported in North Gyeongsang Province, three in Daegu, two in Seoul, and one each in Incheon and Ulsan.

With five more deaths, the death toll rose to 222, putting the country’s overall fatality rate at 2.1 percent. The fatality rate stands at 22.22 percent for those in their 80s and older, 9.29 percent for those in their 70s and 2.47 percent for those in their 60s.

Daegu, once the country’s epicenter of the novel coronavirus, represents the majority of the country’s total cases, accounting for 64.6 percent.

(laeticia.ock@heraldcorp.com)