When Meredith McKee contracted coronavirus in February she thought she'd had a lucky escape from the deadly disease.
The Dallas woman was diagnosed earlier this year after experiencing "clear and obvious" symptoms.
"I had a dry cough, you would not believe. It would not stop," McKee told local TV station NBC 5.
But over the weekend McKee made a devastating discovery – she'd managed to test positive to coronavirus for a second time.
McKee's fresh diagnosis comes amid mounting evidence that catching coronavirus once doesn't make you immune from further cases, despite early hopes it would be the case.
Instead, medical experts now fear there are instances where Covid-19 stays dormant in a patient for several months before rearing its head again.
'HIT ME LIKE A TONNE OF BRICKS'
Last weekend, McKee revealed on Facebook she had been diagnosed with coronavirus for the second time, sharing that it had "hit me like a tonne of bricks".
Posting a tearful selfie of herself in a hospital gown and mask, she warned others to be vigilant.
"I'm here to tell you this is NOT over, it is very real and nothing to be flippant about," she wrote in the caption.
"There are so many unknowns and the CDC (US Centres for Disease Control and Prevention) cannot tell whether the virus was dormant all this time or if it was a new contraction."
She said her symptoms were "very different" this time around and she had been admitted to Dallas' Texas Presbyterian hospital because of her high blood pressure.
'I FELT GREAT'
After recovering from coronavirus in February McKee told NBC 5 antibodies showed up in her system and she donated blood to researchers, feeling certain her ordeal was over.
"I felt great going finally something good is coming out of the hell I've been through, because I'm going to help up to eight people with this plasma," she said.
But last week she began feeling unwell with a headache and high blood pressure, taking herself to hospital to get checked out.
With no traditional coronavirus symptoms McKee didn't think there was any chance she had the disease again – until staff at the hospital made her do another test.
"I would never have known had they not insisted on doing another Covid test," she said, "and I was floored when it was positive."
McKee said doctors now believe she never fully recovered and the disease had simply gone dormant for several months.
She is now "mortified and seriously devastated" at the thought she may have been infecting family and friends since February.
"I thought I was perfectly, perfectly fine," McKee said.
GETTING COVID-19 TWICE: WHAT WE KNOW
At the beginning of the pandemic, scientists were hopeful that the presence of antibodies in the blood after a person recovered from coronavirus would mean immunity.
But experts are still unable to prove if this is the case and are now looking at whether it's possible that some take longer to "shed" coronavirus than others, which would explain why people like McKee can test positive months later.
Similar cases have also been reported around the world, with more than 14 US sailors from the USS Theodore Roosevelt testing positive for coronavirus a second time last month.
Infectious diseases expert at Vanderbilt University Medical Center William Schaffner told NBC News coronavirus may stay in some people's systems for a longer period.
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"It's possible that people could shed remnants of the virus for some period of time. That doesn't mean anything is wrong with them or that they are contagious," Dr Schaffner said.
Instead, another expert believes it's possible that a small percentage of cases experience a "delayed immune response".
"In some persons they begin to feel well again and signs and symptoms including fever decrease, but some then go on to develop respiratory distress and must be provided oxygen in hospital," London School of Hygiene and Tropical Medicine's infectious disease epidemiology professor David Heymann told the The Guardian.
"It appears to be a delayed immune response that is more serious in some persons and that reacts to remaining virus in various organs."