Wards at three hospitals have been affected by an outbreak of unexplained vomiting and diarrhoea.
The outbreak happened on wards at the Royal Gwent Hospital in Newport, Nevill Hall Hospital in Abergavenny and Ysbyty Aneurin Bevan in Ebbw Vale.
Aneurin Bevan University Health Board said there has been an increase in incidents of unexplained diarrhoea and vomiting.
It has asked for children and the elderly not to visit patients at the hospitals "unless urgent".
To prevent further cases, the health board is limiting visitors to two people per bed and asking those with symptoms of diarrhoea and vomiting not to visit for 48 hours.
Staff are being told to report to the nurse in charge before seeing patients.
Those with further questions are asked to contact the Infection Prevention Team on the following numbers:
- Royal Gwent Hospital - 01633 238101
- Nevill Hall Hospital - 01873 732048
- Community Hospital - 07903 324603
