Health officials have contacted more than 200 people who attended a conference in central London after it emerged one delegate is suffering from coronavirus.
Public Health England (PHE) sent a letter to those who were at the UK Bus Summit at the QEII Centre in Westminster on February 6, including several MPs, two of whom have now decided to stay mostly at home.
The person taken ill is one of the nine people diagnosed with coronavirus in the UK.
Dr Yimmy Chow, consultant in health protection at PHE, said: "One of our main priorities has been to identify any people who we think have been in close contact with confirmed cases of Covid-19 to provide public health advice, as they may be at slightly increased risk of catching the virus.
"While the degree of contact conference delegates may have had with the case is unlikely to have been significant, we have taken a precautionary approach and informed them of the situation."
Sources told the PA news agency the bus summit case is not linked to the UK's ninth case of coronavirus, who is a Chinese woman.
The Transport Times emailed delegates and enclosed a letter from PHE saying they should take no action if they were well but to stay indoors, avoid contact with others and call NHS 111 if they developed symptoms such as a fever or cough.
"While the degree of contact you may have had with the case at the summit is unlikely to have been significant, we are taking a precautionary approach and informing you," the letter said.
The bus conference listed about 250 delegates from the nationwide bus and transport industry.
Among the speakers were buses minister Baroness Vere and former parliamentary under secretary of state for transport Nusrat Ghani.
Labour MP for Nottingham South Lilian Greenwood, who also spoke at the summit, tweeted that she had received PHE's letter and had decided to cancel appointments.
She added: "I'm feeling completely well but to be extra-cautious I'm cancelling my public engagements until 20th February. Sorry for any inconvenience."
Labour MP for Leeds North West Alex Sobel, who also attended the summit, said he was not unwell but had decided to stay at home as a precaution.
He has cancelled engagements until the end of next week.
His office told PA he had not undergone any coronavirus testing and was not due to be tested.
He said: "Public Health England gave the advice that I should take reasonable precautions.
"Right now I should be at surgeries with constituents. We thought it a reasonable caution to self-isolate until next Wednesday evening.
"I'm fine. I've got no fever. But as you can present after up to 14 days, I've taken these precautionary measures."
Mr Sobel said he only found out about the risk through the media and was "concerned" other attendees may still not know.
Another attendee, who did not wish to be named, said: "We all received an email. The advice was 'just carry on if you're feeling fine, if you're not, lock yourself up'."
He said he had no symptoms.
It comes as United Airlines confirmed it offered assistance at Heathrow Airport on Friday after a passenger fell ill on one flight.
The total number of confirmed cases globally now stands at more than 67,000.
Australian Associated Press