The Colorado Department of Public Health and Environment asked thousands of Dr. Stephen Stein's former patients to seek testing for HIV and hepatitis after it received notifications that the dentist reused sedation syringes, The Denver Post reported.
Three people so far have tested positive for either human immunodeficiency virus, the cause of AIDS, or hepatitis B or C, but officials said the health department cannot directly link the positive test results to Stein, who is not currently practicing.
And, the department "will not know the number of people who get tested, only the number of positive tests that are reported," said Mark Salley, from the health department.
Salley said an investigation focusing on Stein did "confirm the use of unsafe injection practices" between 1999 and 2011.
The health department urged patients "to get tested -- and, if positive, to check with their healthcare provider for care."