Norovirus hits Morriston, Withybush and Gorseinon wards
Three hospitals in south west Wales have closed wards due to the diarrhoea and vomiting infection norovirus.
Morriston Hospital in Swansea has closed four wards while the city's Gorseinon Hospital has shut one ward.
Visitors to the wards have been asked to stay away until they reopen.
Meanwhile, Hywel Dda Health Board said the norovirus outbreak at Withybush Hospital in Haverfordwest, Pembrokeshire, had worsened, with five wards closed to admissions.
The four wards closed at Morriston are: CDU West, Ward D, Ward E and Ward S.
Abertawe Bro Morganwwg Health Board said patients already on these wards were not being transferred elsewhere and no-one was being admitted to them.
Visiting was only allowed in exceptional circumstances, it said.
The health board said East Wing at Gorseinon Hospital is also closed.
In Pembrokeshire, friends and relatives of patients at Withybush have also been asked not to visit the hospital, while staff available to work are being asked to contact their line managers.
At the hospital, wards seven, 10, 11 and the community services integration unit remain closed to all admissions.
Ward one is also now closed, along with bays on wards three, four and 12.
"We are doing all that we can to ensure emergency services are accessible and this is being helped by staff working additional shifts," said the health board.
"We request that any staff that might be available to work, to please contact their line manager."
Health officials said measures to control infection were in place across the hospital, and routine admissions had been reduced.
The outbreak now affects most wards, and friends and relatives are asked not to visit anyone currently at the hospital.
"Ward staff will do all that they can to give you up-to-date information by telephone," said the board.
"The health board is asking members of the public suffering from diarrhoea and vomiting to not visit any hospital or care facility.
"The health board asks the public to consider if it is absolutely necessary to use services due to the pressure currently being put on its beds."
Other hospitals in Wales have also been hit by the norovirus bug this month.
The Royal Glamorgan Hospital in Llantrisant said at the weekend it was the latest hospital in Wales to be hit by the winter vomiting bug.
Several wards were affected and temporarily closed.
The bug has also hit Ysbyty Gwynedd, Wrexham Maelor, Glan Clwyd, Colwyn Bay and Tywyn in north Wales, as well as Bronglais in Aberystwyth.
Norovirus causes vomiting, stomach cramps, fever and diarrhoea, and is easily spread from person to person.
Symptoms usually begin between 12 to 48 hours after a person becomes infected, with most healthy people making a recovery within one to three days.