Dead Covid-19 particles muddy test results

Coronavirus patients who remain positive weeks after diagnosis may harbour dead virus particles that can’t be distinguished from infectious ones in standard tests, scientists in South Korea found.

The so-called SARS-CoV-2 virus dies one to two weeks after infecting and proliferating inside respiratory cells, doctors at the National Medical Center in Seoul told reporters on Wednesday. Pieces of the virus’s genetic material may remain in cells and be detected by a nucleic acid test a month or two after infection, underscoring the limitation of testing, they said.

How long an individual excretes infectious virus in their respiratory secretions and fecal matter is key to determining the optimal time an infected person should selfisolate or be quarantined. Previous studies indicate that very ill patients typically remain infectious longer than people who experience only a mild illness.

The Korean Centers for Disease Control and Prevention said earlier this month that the coronavirus may be reactivating in people who have been cured of the illness. At the time, the agency found that about 51 patients classed as having been cured tested positive again. It concluded that, rather than being infected again, the virus may have been reactivated in these people.