When an employee of a Sydney supermarket tested positive for coronavirus, after spending time in quarantine and apparently recovering, many people asked the same question: are 14 days in quarantine enough?
Cases like these, where people get rid of the virus and then be positive, are troubling – but major research has shown that there is no reason to be alarmed.
Here’s what you need to know:
- South Korean study found large proportion of people tested positive for COVID-19 after apparently recovering
- Scientists believe positive results were caused by remnants of virus remaining in cells
- There was no evidence that these people were still infectious despite their positive tests
- There was no evidence that someone was newly infected with the virus for the second time.
- The study found that the majority of people who had remnants of the virus also had antibodies that could kill it
Does a positive coronavirus test mean that a person is infectious?
The Korean Centers for Disease Control and Prevention has conducted a major study on this issue after discovering that hundreds of people are still testing weeks and months positive after apparently curing the disease.
The study investigated 285 “positive cases” and followed 790 friends and family with whom they had contact after their second positive test.
After monitoring these 790 contacts for at least 14 days, the study found that 27 were positive.
Of these 27 people, 24 had already contracted the virus before coming into contact with the case studies.
The other three were found to have other likely sources of infections.
Professor Collignon said that the epidemiological study showed that people who tested positive, after appearing to have eliminated the virus, did not appear to be infectious.
“But just to see if there was a chance they might have missed something, they said, ‘let’s look at this in the laboratory,'” he said.
To support their results, the researchers took samples from 108 of these positive cases and tried to grow them in cell culture.
“They took a special cell line called Vero, and they put material in people’s throats to see if it would grow and develop in more numbers in these cell lines – and it doesn’t” said Professor Collignon.
Similar results have been reported in smaller studies in France and the United States.
Why are people negative and then positive?
University of Western Sydney virologist Dr. Sacha Stelzer-Braid said swab tests used in Australia were extremely sensitive and detected the virus even when it was no longer infectious.
“It collects very small parts of the viral genome, so it does not collect all of the virus,” she said.
Professor Collignon said that the “re-positive” cases with symptoms, probably had a common cold causing these symptoms – and just happened to have an inactive coronavirus in their bodies too.
“It is more likely that they are sick from the other virus and if it is really late after they have been quarantined and after we know they have recovered … that it it is a small, unsustainable virus that exists, rather than an active infection.
“It may be the cold virus, for whatever reason, that kills a few more and more cells [remnants of coronavirus] to be freed.”
Can you catch COVID-19 twice?
Professor Collignon said that so far it seems that people are not re-infected with the virus once they already have it.
“There is no evidence that anyone who had an infection and recovered from it was infected a second time with a new virus,” he said.
“We are still in the early days, we only have six months of data after the first infections. But so far, it seems that infected people only get it once.”
The South Korean study found that 96% of those who still had remnants of the virus also had antibodies.
“It makes them less likely to be infectious to others because the virus they had in their bodies should have been killed by the antibodies they found.”
“It also means that they appear to be immune.”
So 14 days of isolation should be enough?
Dr. Stelzer-Braid said that two weeks of isolation was enough.
“There is really good evidence that there is enough time for people’s symptoms to go away and their viral load to reach a very low level, which is either undetectable or very close to the detection limit”, a- she declared.
“This means that they cannot infect anyone else and this is in line with the World Health Organization guidelines for the release of people from the hospital and quarantine.”
Professor Collignon said that based on the research, there was no reason to question the 14-day isolation policy for returning travelers or anyone likely to have been in contact with the virus .
But he suggested that everyone should be tested after those 14 days, especially if they hadn’t tested positive at the start.
“The advantage of testing people before they leave [quarantine] this is in case there are asymptomatic people, “he said.
“You will want to isolate them longer because they may not have developed the infection until day 10 and they may be infectious for about a week at that time.”