Some NHS workers have been received letters asking them to be retested for Covid-19 following concerns previous tests were faulty.
Health minister Helen Whately told Sky News that early tests were evaluated and found to be “not effective enough”.
A total of 61 NHS staff are known to have died after becoming infected with the coronavirus, according to Ms Whately.
The revelation means that some staff could have returned to work while being infected with the virus.
Helen Whately told Sky: “Some of the early tests were evaluated and the evaluation was actually they were not effective enough.
“Those who were tested with the test that weren’t up to scratch have been written to to let them know they will be offered another test.”
The Department of Health said 17,337 patients have died in hospital after testing positive for coronavirus in the UK as of 5pm on Monday, up by 828 from 16,509 the day before.
Coronavirus was linked to a third of all deaths in England and Wales in the week up to April 10, with the total number of care home deaths increasing almost six-fold in seven days to more than 1,000, according to the Office for National Statistics (ONS).