Positive test results for Hepatitis C have been found in patients of a health care worker diagnosed with the disease.
Thousands of tests for Hepatitis C were carried out in Gwynedd
More than 2,000 people in Gwynedd were tested after it was revealed a health worker was carrying the infection.
The National Public Health Service for Wales and Gwynedd Local Health Board said there was no evidence to link the positive tests with the health worker.
Health officials said it was "inevitable" positive results would be returned from a large number of tests.
Thousands of patients were invited for tests after it was revealed in May that the health care worker had been diagnosed with Hepatitis C.
The disease is spread when blood of an infected person is spread into the bloodstream of another and leads to inflammation of the liver.
About 2,300 people in Gwynedd were given blood tests.
Sandra Payne, regional director for North Wales for the National Public Health Service said: "As we expected, the vast majority of these results have been completely normal.
"This confirms that the risk to patients has been extremely low.
"It is inevitable when testing a large number of people that some will have positive results, reflecting background levels of infection in the population.
"This does not mean that infection was passed on by the health care worker.
"Indeed, we currently have no evidence that a single person has been infected in this way."
The exact number of patients to return positive Hepatitis C tests has not been revealed.