Gordon Murray entered his pub, An Bothar Rua on Saturday night while waiting for the results of his test, where there was an 18th birthday party being held according to The Irish Times.
The pub in Elphin is now closed after Mr Murray subsequently tested positive for the virus, saying there were about 50-60 people in the pub when he entered at the weekend.
“I will put my hands up and say I didn’t know I had to self-isolate. If I knew I was supposed to, I would not have been at the bar on Saturday,” he said.
Close contacts of those who have tested positive in the area are now being traced and public health officers have examined the situation in the community.
Following a spike in cases in the area, the town has cancelled First Holy Communion celebrations that were due to take place this Saturday, as reported in the Roscommon Herald.
Parish priest, Fr John Joe Gannon urged the community to follow public health guidelines "to the letter of the law" while a restaurant owner in the town called for people to "put the blame game aside.
Conal Tiernan of the Elf Inn Restaurant said: “It is actually getting us nowhere starting this blame game. We want to rally everyone together and learn from mistakes."