A former member of the General Dental Council has likened the handling of the case of a dentist from Gwynedd infected with hepatitis C to a "witch hunt".
The dentist tested positive for the disease in October 2005
The health authorities wrote to 5,000 patients offering them various tests after the man was diagnosed with the disease, which over 1,000 accepted.
Brian Lux, president of the Dental Practitioners Association, questioned whether all the tests were necessary.
The National Public Health Service said decisions were carefully considered.
The dentist, who is not being named, reported he was infected with hepatitis C in October 2005.
Many past and present patients took tests, including ones for hepatitis B and HIV, although no evidence was found to link any infection to the man.
Mr Lux, who has been advising the dentist, said it was not necessary to screen for HIV and hepatitis B as well, and questioned whether the screening was necessary at all.
"Are you telling me you are not so strapped for cash you can waste - and I do say waste - this money on a useless exercise which denigrated a dentist, which put him under terrific pressure where he nearly had a nervous breakdown, all for what?
"For nothing. We said at the outset you wouldn't find anything and you didn't.
"What were you trying to prove at the public expense? I think we need some answers."
Mr Lux, who likened the case to a "witch hunt", said it would have been fine to do a "lookback exercise" to check for hepatitis C.
Special clinics were set up around Gwynedd to carry out the tests
However, he added: "There was no rhyme or reason to include hepatitis B and certainly it was an insult to the integrity of the dentist concerned to suggest by innuendo that he had HIV by saying, well have a test for HIV as well."
Special clinics were run around Gwynedd to cope with all the screening.
The National Public Health Service said the exercise had not been completed yet and every decision had been carefully considered.
It added contacting patients was the only way to clarify whether people were at risk.
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.