Three wards at Wrexham Maelor Hospital which are closed following a high number of norovirus cases are not expected to reopen until after the weekend.
On Friday Betsi Cadwaladr University Health Board said 11 patients had shown symptoms over the previous two days.
Patients due to attend appointments and with symptoms are asked to telephone the ward for advice before visiting.
Anyone suffering from diarrhoea, vomiting or an upset stomach in the last 48 hours is asked not to visit the hospital.
Betsi Cadwaladr University Health Board have confirmed that there are now 12 patients showing symptoms of Norovirus at the Wrexham Maelor Hospital.
Nine patients at Wrexham Maelor Hospital are suffering from an outbreak of Norovirus.
Betsi Cadwaladr University Health Board say two wards have been affected by the outbreak, and admission to those wards has been suspended until patients' symptoms have gone.