Two wards of a hospital have been closed after an outbreak of coronavirus cases, a health board has announced.
Cwm Taf Morgannwg health board said it was taking "robust action" after 34 positive cases at the Royal Glamorgan Hospital in Rhondda Cynon Taf.
Latest Public Health Wales figures show the health board accounted for 25 of 31 Covid-19 infections "probably" or "definitely" caught while in hospital.
The health board said early evidence suggested the outbreak was "contained".
Measures put in place include the closure of the affected wards, increased testing of staff and patients and limits on "social visiting".
In July, PHW revealed hundreds of patients had caught coronavirus while in hospital.
These included high numbers of hospital infections in Aneurin Bevan health board in March, followed by Cwm Taf and Cardiff and Vale health boards in April.
Betsi Cadwaladr health board, in north Wales, saw a spike in so-called hospital onset Covid-19 infections in July, which centred on Wrexham Maelor Hospital.
A separate study of 1,500 hospital cases in the UK in April found one in eight patients who had received coronavirus treatment had caught it while in hospital.
"The health and wellbeing of our patients and staff is our number one priority and we take infection prevention and control measures extremely seriously," said Dr Kelechi Nnoaham, Cwm Taf's director of public health.
"I would like to reassure the public that immediate action has been taken to address this outbreak, and although it is too early to confirm the end of the outbreak, early evidence suggests that this has resulted in the number of infections transmitted within the hospital being contained."
Dr Nnoaham added it was "vital that we all play our part" in helping reduce the spread of coronavirus.