Ten patients and 11 staff at Craigavon Area Hospital are now confirmed to have Covid-19, after two clusters were identified on the site.
On the Haematology Ward, where blood disorders are treated, ten of the 12 ward patients have tested positive.
Eight members of staff on the ward have also tested positive. They are off work and self-isolating.
All other staff members on the ward are being tested again as a precaution.
An investigation into the clusters is continuing.
Dr Sara Hedderwick is an infectious medicine consultant with the Southern Health and Social Care Trust.
“Obviously it’s concerning to us whenever we have patients with Covid and it’s particularly concerning when those are vulnerable people or immuno-compromised like our haematology group of patients are,” she said.