Twenty members of staff at Craigavon Hospital are self-isolating after colleagues tested positive for Covid-19.
The Southern Health Trust has confirmed that three staff members at the hospital's respiratory emergency department have tested positive for the virus.
On Tuesday morning 20 members of staff were self-isolating as a precaution, the Trust said.
In a statement, the Trust said any other members of staff who have been in close contact with the confirmed cases are being tested and are currently at home isolating as a precaution.
"At this stage it is understood that the infection may have transferred in a social setting, ie not within the Emergency Department (ED)," the Trust said.
"Staff in the ED wear full personal protective equipment when treating patients, therefore we do not believe there is any risk to patients at this time.
"The ED in Craigavon remains open but is extremely busy and we would urge the public only to attend if there is no other alternative."
According to the department of health's daily coronavirus infection figures, 359 individuals have tested positive for Covid-19 in the last seven days.
The highest number of cases over the last seven days have been in the Mid and East Antrim Council area (95) followed by Belfast (76) and Antrim and Newtownabbey (44).
The current estimate of the virus reproduction number in Northern Ireland is 1.0 - 1.6 according to the region's department of health.
