London (CNN) UK Prime Minister Boris Johnson issued a statement Saturday thanking the National Health Service staff at St. Thomas' Hospital following his treatment for coronavirus, saying "I can't thank them enough. I owe them my life," according to the UK Press Association.

This is the first known statement from the Prime Minister since he entered hospital last Sunday night.

Johnson announced he tested positive for the novel coronavirus on March 27. He said he was experiencing "mild symptoms" and would continue leading the country -- while self-isolating in his apartment in Downing Street.

But 10 days later, 10 Downing Street announced the 55-year-old was not getting better and was taken to St. Thomas' Hospital in London. He was moved to an intensive care unit (ICU) the next day after his condition deteriorated.

Johnson spent three nights in intensive care and received "standard oxygen treatment," according to his spokesman, but did not require mechanical or invasive ventilation.

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