A hundred workers at a hotel in Co Offaly are being screened after about 20 people who stayed there last week tested positive for coronavirus.
GPs in Tullamore have been warned they're facing "a significant Covid-19 incident".
The party of 40 checked into the Bridge House Hotel in Tullamore the weekend before last, and stayed for several days.
They played golf nearby, and some socialised at a number of pubs and restaurants in the town.
A letter sent to GPs there says up to half of that group have since tested positive for Covid-19.
So far, there are no known infections beyond that original group.
But public health teams are moving to trace guests from across the country to say they may have come into contact with a case.
And they've warned local doctors they that "a significant number of people" in Tullamore may be affected if there has been further spread.
Management at the Bridge House say they're "working closely with and cooperating with the HSE" and that they've closed temporarily.
They say they've worked "tirelessly" to set up "a safe environment in line with public health guidance".