One of the people diagnosed with coronavirus in the UK attended a conference near parliament last week along with about 250 other delegates.
The patient, who has not been named, attended the UK Bus Summit at Westminster's QEII Centre in central London on 6 February.
The event was described as the "premier bus event covering all parts of the UK".
Speakers and attendees included "key decision makers in government from around the UK" as well as bus and coach industry representatives.
Among the speakers listed were buses minister, Baroness Vere; junior transport minister, Nusrat Ghani – who lost her job in this week's government reshuffle; and various managing directors of bus firms.
The summit was organised by Transport Times, which emailed attendees on Thursday to inform them that a person suffering from COVID-19 – the disease which is caused by the coronavirus – had been at the event.
The Financial Times reported Transport Times sent the email on the instruction of Public Health England (PHE).
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It also included a letter from PHE which told conference attendees to 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, as reported by the newspaper.
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."
It is said the case is not linked to the ninth patient with coronavirus in the UK – a woman from China who took an Uber to A&E after she developed symptoms.
NHS chief executive Sir Simon Stevens said on Thursday many more people in the UK may need Read More – Source