Clinics have opened in Gwynedd for patients of a health worker with hepatitis C to be given blood tests for the disease.
Twelve of the 47 clinics offering blood tests are fully booked
More than 1,000 patients have signed up to have the tests. They can also choose to be screened for hepatitis B and HIV.
Almost 1,800 people have called a confidential patient helpline and 12 of the 47 clinics are now fully booked.
The National Public Health Service (NPHS) for Wales has stressed the risk to patients is "very small indeed".
The NPHS discovered in October that the member of staff, who was understood to have worked at a dental surgery, had hepatitis C.
About 5,000 patients have been sent letters with the phone number for the confidential hotline for patients to book blood tests.
When the hotline opened last Wednesday, 717 people called on the first day.
Special blood testing clinics are being held around Gwynedd between 5 June and 17 July.
Sandra Payne, regional director for the NPHS for Wales, said: "They're being offered the opportunity to have three virus screens: hepatitis C, hepatitis B and HIV - but if they don't want all three they can pick one or two."
Dr Payne told BBC Radio Wales patients should ring three weeks after their appointment to find out the results, but said people would hear through their doctor if there was a need for further tests.
She added: "This is a precaution that we're offering people this test on the basis that the risk is very small indeed."
Hepatitis C leads to swelling or inflammation of the liver. The virus is blood borne and is spread when blood of an infected person is spread into the bloodstream of another.
The infection affects different people in different ways, with many experiencing no symptoms at all while others experience extreme tiredness and can feel very unwell.
Reported symptoms include fatigue, weight loss, nausea, flu-like symptoms, problems concentrating, abdominal pain and jaundice.
It is estimated that around 15-20% of infected people clear their infections naturally within the first six months of infection.