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https://www.wsj.com/articles/south-koreas-new-coronavirus-twist-recovered-patients-test-positive-again-11587145248

SEOUL—More than 160 South Koreans have tested positive a second time for the coronavirus, a development that suggests the disease may have a longer shelf life than expected.

Many had volunteered for re-examination after exhibiting symptoms such as coughing. Others submitted to extra testing on little more than a hunch despite not showing symptoms. So far, these patients—all of whom needed to twice test negative before leaving medical supervision—haven’t spread the virus to others, local health officials say. 

The initial belief, according to South Korean doctors directly involved with a government review, is that the virus has “reactivated” in the patients, meaning the disease went dormant and came back. The research remains ongoing and inconclusive. The Seoul government’s report will take at least a month to complete, they say.

South Korea is closely watched as an early indicator of how Covid-19 lingers across a population, having flattened its curve of new infections and now contemplating an unwinding of social-distancing measures. The results showing people testing positive a second time could signal a worrisome potential for the virus to linger that could impact health policy.

South Korean SlowdownThe country was the first to hit 8,000 casesapart from China, though new infections haveleveled off in recent weeks.Cumulative casesSource: Johns Hopkins

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“It may be that you have to test these recovered people every month for symptoms or viruses,” said Mary Guinan, a former chief scientific adviser to the U.S. Centers for Disease Control and Prevention director. “Maybe it comes and goes. We don’t know.”

The development could add extra pressure on governments’ testing supply and availability. It also raises the stakes for those who fall ill, as their battle against the disease may last much longer than previously imagined. China, Japan and India have also reported cases of recovered patients testing positive again.

Medical experts are still struggling to understand many aspects of the new coronavirus and the disease it causes, Covid-19. The coronavirus appears to colonize in the human body in two stages. Initially, the upper respiratory passages of the nose and sinus are infected. As the infection progresses and becomes more severe, the virus spreads into the lower respiratory tract and the lungs, where the virus may linger and become more difficult to detect by testing kits used world-wide.

Prior coronavirus strains, such as MERS and SARS, didn’t have significant cases of reactivation or reinfection, dissipating quickly after the first time a person gets ill, said Deenan Pillay, a virology professor at University College London.

South Korean health officials and advisers, based on their initial review of the results, don’t suspect inaccurate testing to be a culprit. Test-kit makers and laboratories say South Korea’s kits have a 95% sensitivity to the coronavirus.