London (CNN) UK Prime Minister Boris Johnson will not be tested for coronavirus, despite one of his ministers testing positive for coronavirus, raising fears about the potential spread of the disease in Westminster.

Nadine Dorries, who attended a reception with the PM and his fiancé Carrie Symonds in Downing Street last Thursday, said in a statement on Tuesday that she had been diagnosed with the virus and is in self-isolation.

A government source said on Wednesday Johnson would not be tested, as he was displaying no symptoms and had not come in close contact with Dorries at the event. They pointed out the current medical advice claims you would need to be within 2 meters of someone carrying the infection, which Johnson at no point was.

Health officials are now racing to trace those who have had contact with Dorries, who has kept a busy diary of engagements in and around the UK's political center.

"I can confirm I have tested positive for Coronavirus," Dorries, a junior health minister, said in a statement released through the Department of Health. "As soon as I was informed I took all the advised precautions and have been self-isolating at home."

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