NHS Grampian said the number of positive tests arising from an outbreak at The Hawthorn Bar in Holburn Street now stands at 27, having been 13 on Sunday.
The pub said the cluster was linked to customers who visited on July 26.
Dr Emmanuel Okpo, consultant in public health medicine, said: “It is not entirely surprising further cases have been detected.
“This virus is still circulating in our communities. It poses a risk to all of us.
“People who have not gone to this bar or who live in other parts of Grampian, should not assume they are somehow safe.
“Anyone who develops symptoms of Covid-19 – a loss of their sense of taste or smell, a fever, or a new, continuous cough, should isolate at home immediately and arrange a test.”
It comes after First Minister Nicola Sturgeon said images of packed pubs “made me want to cry” when she announced 18 new Covid-19 cases in Scotland – including 11 in Grampian.
The health board said colleagues at Aberdeen City Council are in contact with licensees to reiterate the safety rules and regulations.
Investigations into the cluster remain ongoing.
A post on the pub’s Facebook page said: “We assure all customers we have been and continue to do our utmost to protect their safety and we continue with strict rules and measures in place.
“We do ask all customers to be extra vigilant and adhere to our policies at ALL times.
“Our thoughts are with those affected and we wish them a speedy recovery.
“Please consider this is a very difficult time for us and we hope our customers continue to support us throughout.”
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