5,500 patients in several parts of Wales are being contacted by health boards this week, over fears that they may have been passed the Hepatitis C virus by a healthcare worker.
Obstetric and gynaecology patients will receive letters, offering them advice and a blood test for Hepatitis C.
The worker, who has now retired, is known to have transmitted the virus to two patients between 1984 and 2003.
They worked in the Aneurin Bevan health board area between 1984 and 2003, predominantly at Caerphilly District Miners' Hospital.
They also briefly worked at the East Glamorgan General Hospital in Pontypridd in 1984, and at Wrexham Maelor Hospital (known then as Maelor General Hospital) in 1978.