Dorries, a health minister, is first MP to be diagnosed with Covid-19. She confirmed on Tuesday evening she had been self-isolating at home.
The MP for Mid Bedfordshire attended a gathering in No.10 on Thursday, along with the prime minister, to mark International Women’s Day.
Downing Street said today Johnson had not come into close contact with Dorries at the event and had no symptoms of the virus.
The Department of Health and Social Care (DHSC) said ministers would not need to undergo testing as Public Health England (PHE) worked to advise those who have been in close contact with Dorries.
PHE said it had assessed the risk of Dorries’ individual close contacts and only those with symptoms need to self-isolate.
For each Covid-19 case, a risk assessment is carried out and advice tailored to that group, a spokesperson said.
Labour MP for York Central Rachael Maskell said she was self-isolating on the advice of 111 following a meeting with the health minister last Thursday.
It comes as MPs prepare to pack into the Commons chamber to hear chancellor Rishi Sunak unveil his Budget.
In a statement, Dorries said: “As soon as I was informed I took all the advised precautions and have been self-isolating at home.
“Public Health England has started detailed contact tracing and the department and my parliamentary office are closely following their advice.”
She later tweeted thanks to her well-wishers, adding: “It’s been pretty rubbish but I hope I’m over the worst of it now.
“More worried about my 84yo mum who is staying with me and began with the cough today. She is being tested tomorrow. Keep safe and keep washing those hands, everyone.”
On Wednesday morning a 53-year-old British woman was reported to have died from Covid-19 in Indonesia, with the Foreign Office offering support to her family.
The news came after the number of cases in the UK rose to 382, and a sixth death in the UK was confirmed on Tuesday.