A reader, CSG, asked me a question. She knew someone who became ill and tested positive for COVID-19. That person has since recovered and asymptomatic. The problem is the repeat nasal swab after 2 months is still positive.
Because of the positive repeat test, it is believed that the person is still infectious and so the quarantine for that person was extended even though he is asymptomatic.
Are people who tested positive again for Covid-19 still infectious?
Not anymore, according to a study done by the South Korean Centers for Disease Control (KCDC). People who test positive again or re-positives are not infectious anymore.
How Does the KCDC know Re-Positives are not Infectious?
They tested 447 cases of re-positives and 790 of their contacts.
Among the 790 contacts, only 3 tested positive for the COVID-19. Two of the 3 had a negative viral culture. In 1, the RT-PCR test was indeterminate to culture a virus.
The three who tested positive most likely had Covid-19 before but were asymptomatic and therefore were not tested.
44.7% of the re-positives have new symptoms suspicious for Covid-19. In all of them, no SARS-CoV-2 virus grew when cultured.
The KCDC also tested for eight other respiratory viruses in those with symptoms, and 3 cases were positive for another virus.
To summarize, the study showed that 447 people who are re-positive for Covid-19 did not infect their 790 contacts.
The three of the 790 who tested positive got their infection from someone else, and those three are also not infectious.
No SARS-CoV-2 virus grew when they cultured the samples from all the re-positive cases.
So if they are not infectious for Covid-19, why did they test positive?
The standard test to detect Covid-19 is RT-PCR. The RT-PCR measures the amount of nucleic acid of the SARS-CoV-2 present in the sample.
A positive test can mean the presence of viral nucleic acid remnants or viruses that are not capable of replication to cause infection.
What is also notable in their study is that in all re-positive cases and newly confirmed cases, neutralizing antibody production against SARS-CoV-2 was found from the first serum.
That means it is very likely that the antibodies formed against Covid-19 are effective in preventing another infection.
Based on this study, the KCDC changed its recommendations about Covid-19 for South Korea. Below is from the KCDC
Management of confirmed cases after discharge from isolation and managemeant (treatment) of re-positive cases will no longer be conducted. (Effective 0:00 of 19 May)
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Before |
After |
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Management of confirmed cases after discharge from isolation |
14-day self-isolation recommended after discharge from isolation |
Not needed |
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PCR test required if symptoms appear within 14 days of discharge from isolation |
Not needed |
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Management of cases that test positive after discharge from isolation |
Re-positive cases managed similar to management of confirmed cases (isolation) |
Not needed |
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Contacts managed similar to management of contacts of confirmed cases (quarantine) |
Not needed |
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Investigation of re-positive cases |
Reporting of re-positive cases and investigation |
Same as before |
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Investigation of contacts of re-positive cases |
Same as before |
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