Enlarge /. The medical staff transports patients from a sanatorium where mass infections with coronaviruses occurred on March 19, 2020 to a hospital in Daegu, South Korea.
View more stories
People who recover from COVID-19 but test positive for the virus days or weeks later do not excrete virus particles and are not infectious. This comes from data released on Tuesday by the Korea Centers for Disease Control and Prevention.
The so-called "re-positive" cases have raised concerns that infection with the new SARS-CoV-2 coronavirus could "reactivate" in recovered patients or that post-infection recovery may not even cause short-lived immunity. Patients can be reinfected immediately if they are exposed.
The new data from Korea should alleviate these concerns.
KCDC researchers examined 285 cases that had previously recovered from COVID-19 but then tested positive again. Patients were tested positive again between one and 37 days after recovery from their first infection and release from isolation. The average time to a second positive was about 14 days.
Of these cases, the researchers checked 284 for symptoms. They found that 126 (about 48 percent) actually had symptoms related to COVID-19.
But none of them seemed to have spread the infection. KCDC examined 790 people who were in close contact with the 285 cases and found that none of them were infected with the "re-positive" cases.
It was crucial that additional tests of 108 “re-positive” cases showed that none of them released infectious viruses.
KCDC on RT-PCR for SARS-CoV-2
The type of tests that indicated that the 285 people were positive for COVID-19 a second time were so-called RT-PCR tests (reverse transcription polymerase chain reaction). These tests are typically used to diagnose COVID-19 infection. To do this, they recognize and copy unique, targeted fragments of the genetic material of SARS-CoV-2.
In this way, you can determine precisely and effectively whether someone is infected with the virus. If someone has SARS CoV-2 gene material in their airways, they are infected. However, genetic material does not necessarily mean that the person still has an active infection and infectious virus particles. You may only have fragments of genetic material from destroyed virus particles.
This seems to be the case here. When KCDC researchers tried to isolate and grow whole infectious particles of SARS-CoV-2 from the 108 cases they could test, all 108 were negative for the entire virus.
When they performed further blood tests in 23 of the re-positive cases, almost all (96 percent) had neutralizing antibodies against SARS-CoV-2. This indicates that they may have some immunity to reinfection with the virus.
It is unclear what caused symptoms in many patients. Some cases tested positive for other respiratory viruses, but many did not.
However, based on the data, the KCDC found that re-positive cases are not infectious and do not need to be isolated again.