There is no evidence that a dentist suffering from hepatitis C infected any patients, a report by the National Public Health Service for Wales says.
The lab costs for the 2,665 patients tested was £50,000
Half of the 5,000 patients at the unidentified Gwynedd dental practice were tested for the virus.
Eleven patients did return positive results, but all had different types of hepatitis C from the dentist.
However, the report found some gaps in the system, which it asked the Welsh Assembly Government to review.
On Wednesday, a 77-page report was published on the findings of the team set up to investigate any possible risk from the dentist since he tested positive in October 2005.
The National Public Health Service (NPHS) in Wales, working with the Gwynedd Local Health Board (LHB), referred the finding to the United Kingdom Advisory Panel where experts decided what action should be taken.
They recommended the matter be investigated because there was "concern about infection control practices" where the dentist worker worked.
According to Dr Sandra Payne, regional director of public health for the NPHS, it was a "belt and braces approach."
She said the results of the report - which does not identify the worker or confirm he is a dentist - were as they expected.
She added:"We have found no evidence of anyone being infected with hepatitis C by the healthcare worker or at the healthcare worker's place of work.
"The numbers of patients who tested positive for hepatitis B and C are what we would expect in a population of this size.
"There is no evidence of a single patient being infected with hepatitis by blood-to-blood contact with another of the health care worker's patients.
'No greater risk
"Overall, the evidence shows that patients of the healthcare worker are at no greater risk of infection than the wider population. As such, there is not need for any further action."
Dr Payne said the incident management team behind the investigation has recommended the assembly government to consider its findings.
"There are issues around the inspection and regulation of healthcare workers in private practice and around the occupational health services available to such workers," she added.
She said gaps in the system leave certain types of private healthcare "beyond inspection and regulation and where there is no support to the healthcare worker".
Grace Lewis-Parry, chief executive of Gwynedd LHB, said 100 staff worked on the "look-back" exercise.
Letters to patients, with staff overtime and telephone calls, were estimated to have cost between £10,000 and £12,000.
The laboratory costs for blood tests was around £50,000.
She said it was impossible to measure the staff costs, because employees stopped doing other work and "concentrated on priorities".