Recovered patients are getting reinfected
In South Korea, which has been lauded for its comprehensive COVID-19 testing strategy, some patients who had been cleared of COVID-19 infection have tested positive again. On Tuesday, the Korean Centers for Disease Control (KCDC) reported that eight more recovered patients have received similar results, bringing the total of “relapsed” patients in the country to 124.
But the reinfection cases in South Korea aren't the only ones being reported. In China's Guangdong province, health officials have found that 14 percent of recovered patients are retesting positive for the coronavirus. This number includes a patient who died five days after he was discharged and tested negative more than once. In Wuhan, ground zero of the coronavirus pandemic, up to 10 percent of cleared patients are also testing positive for a second time. Meanwhile in Japan, at least one recovered patient -- a tour guide from Osaka -- has tested positive again after previously testing negative for the coronavirus.
The emergence of a new, mutant strain of the coronavirus (SARS-CoV-2) responsible for the outbreak in many countries is just one possible reason why reinfections are happening. Talking to Fox News, Nesheiwat enumerated several other possible reasons that could be causing these cases.
False negatives due to sampling errors
One very likely explanation, according to Nesheiwat, is that the patients had previously gotten “false negative” results. This means that the patients still had the virus in their systems when they got tested, but the test was somehow unable to detect the virus. This could be because the sampling was done incorrectly.
“Maybe when whoever was conducting the nasal swab, for example, they didn’t get enough specimen which means they will get a ‘false negative’,” Nesheiwat explained.
While the sampling procedure is straightforward -- it simply involves inserting a swab deep into a suspected patient's nose -- it's still easy for clinicians to make mistakes.
“It’s not rocket science, but you have to be trained to do it,” said Catherine Klapperich, the director of the Laboratory for Diagnostics and Global Healthcare Technologies at Boston University.
Inaccurate testing also giving positive results
Issues with testing could also be behind the positive results some previously cleared patients have received. According to experts, the PCR test used to detect the presence of the virus is not sensitive enough to distinguish between an active virus and a residual virus.
“What many people don’t understand is that PCR tests simply for the virus’ genetic material and it is not an assay for active virus,” said Richard Condit, a molecular biologist and professor emeritus at the University of Florida College of Medicine.
While recovering from a viral infection, the body clears what Condit calls the “virus litter,” or the inactive debris of viral cells, from the lungs. There are times, however, when patients cough this litter up into their throats. If they get tested after doing so, the test might mistake this for an active infection when, in fact, it is not.
Dormant viruses resurging
Another possible explanation as to why recovered patients are testing positive again could be that the amount of the virus in their bodies had previously dipped to a point where it could no longer be detected, hence the negative results. However, their viral loads may have spiked again sometime after being discharged, resulting in their current situation.
“They could have had low levels [of the virus] that the test wasn’t picking up and started to replicate again,” said Brianne Barker, an associate professor of biology at Drew University in New Jersey.
Other viruses are known to reactivate after long periods of latency in the body. One example of this is the varicella zoster virus, the herpesvirus responsible for chickenpox and shingles.
Tracking new strains
If the cause for these strange results some recovered patients are getting is indeed a new mutant strain of SARS-CoV-2, then it isn't something unprecedented. Scientists have been tracking at least eight different strains of the coronavirus across the globe since the outbreak that started in Wuhan became a massive pandemic.
The question now is whether reinfections are indeed happening because of new strain and, more importantly, if this new strain can prevent people from gaining immunity. In South Korea, the KCDC is already hard at work trying to answer these questions.
“The virus will be divided and incubated, and genes will of course be analyzed,” said KCDC Deputy Director Kwon Jun-wook. “We are closely looking into possible genetic changes.”
The good news is that the coronavirus responsible for the current pandemic does not mutate very fast. According to Kristian Andersen, a professor at Scripps Research, the virus mutates 10 times more slowly than the influenza virus.
“The current virus strains are still fundamentally very similar to each other,” Andersen explained. If this is the case, then scientists should be able to catch the emergence of new ones.
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