A care worker has tested positive for coronavirus twice, becoming the first known such case in the UK, it has been reported.

Mum-of-two Heidi Kray - not her real name - says she is awaiting results to confirm she's clear of Covid-19 for a second time after the "hardest time of her life".

The 31-year-old from Reading first fell ill in March with shortness of breath, a high temperature and blood pressure and so went to a test centre in early April where she tested positive.

She was left bedridden for days while she quarantined, but tested negative after two weeks of isolation.

For updates on coronavirus, follow our live blog HERE.

Retired elderly man looking at smiling female nurse

Then by June the symptoms returned and she was hospitalised, though tested negative again.

But two weeks ago, as she prepared to return to work, she took a fourth test and despite having no symptoms for the virus, was shown - to her surprise - to be positive.

In the next couple of days she expects the results of a home test - the others have all been done by professional medics - to come back negative.

She is the fifth person in the world to get the killer bug more than once.

Fifteen people in the friendship group tested positive
Doctor hand holding positive Coronavirus or Covid-19 rapid test

She told The Sun: "I always thought that if you develop coronavirus once then you are immune after that, but maybe I’m a special case.

"When I caught it the first time, it was almost expected given the nature of my job. But I never expected to get it twice."

Referring to the second time she tested positive, Heidi said: "I had no symptoms. I got the occasional headache of an evening but that is the only thing I could think of that was any different."

She has urged people to follow government advice and admits she has been lucky.

A nurse is seen swabbing the occupants of a car at a drive through Covid-19 testing station

The first person to be officially reinfected was an IT worker from Hong Kong who was first struck down in March before testing positive a second time in August after visiting Spain, via the UK.

Like Heidi, he had no symptoms during his second bout, with analysis suggesting he had caught two "two completely different" strains.

It comes after news surveys of the spread of coronavirus using antibody testing may be underestimating the number of people previously infected by the virus, researchers have said.

In an article, published in the BMJ on Thursday, the researchers said that large-scale seroprevalence surveys may not capture all the people who have developed an immune response to the virus.

Seroprevalence surveys estimate the proportion of the population that have previously been infected with a virus by measuring the presence of antibodies produced.

The team of researchers, from Medical Research Council Biostatistics Unit at the University of Cambridge, University Hospital Wales, and St George's, University of London and St George's Hospital, said these are important for calculating hospitalisation and fatality rates.

Meanwhile, antibody levels against the novel coronavirus rose and then held steady for up to four months in more than 90% of recovered Covid-19 patients in Iceland, according to a study published on Tuesday.

In previous studies, antibody levels dropped sharply within a few months after Covid-19, raising questions about the duration of immunity that infection may provide.

The new finding may have implications for reinfection risks and vaccine durability, said Kari Stefansson, chief executive of deCode Genetics, which conducted the study.