Beti Cadwaladr University Health Board says it is managing outbreaks at two medical wards at Ysbyty Gwynedd and a ward at Ysbyty Eryri in Caernarfon.
Gill Harris, executive director of nursing and midwifery at Betsi Cadwaladr, said: “As of this morning, we are caring for 34 patients with Covid-19 infection across both sites, of which we currently have 14 patients which are confirmed hospital acquired infection.
“A programme of staff and patient testing is underway and our priority is to bring this outbreak to a close as soon as possible.
“All patients who have tested positive are being appropriately isolated and the wards affected are currently closed to admissions and visitors.
“In recent weeks, cases of Covid-19 have continued to increase in our community and we have seen a rise in the number of patients admitted to our hospitals needing treatment due to contracting the virus.
“This is a timely reminder that the virus has not gone away and we would urge anyone who has not received their vaccination to visit our website to book an appointment or visit one of our drop in clinics."
Responding to news of the outbreaks, Sian Gwenllian, Plaid Cymru MS for Arfon said: “These latest hospital outbreaks are a terrible reminder that Covid is not gone, and great care is still needed.
“This is of particular concern given the backlog that we know that every hospital is facing, and the increased pressure from so many visitors to tourist areas such as north-west Wales."