The patient, who has not been identified, attended the UK Bus Summit in the QEII centre.
It read: "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."
Transport Times, which coordinated the gathering, told the Financial Times that it has "distributed a letter of guidance from PHE to all attendees” and was working closely with health officials.
The Standard has contacted Transport Times for comment.
Public Health England guidance has been advising anyone who thinks they may have symptoms of coronavirus to stay at home and call NHS 111.
Authorities will send out a specialist team if needs be.
On Thursday, the Department of Health said 2,521 people in the UK have been tested. Of those 2,512 were confirmed negative and nine positive.
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