(CNN) -- An investigation into an Oklahoma dentist accused of potentially exposing patients to disease confirmed one case of patient-to-patient transmission of hepatitis C, Oklahoma officials said Wednesday.
A total of 89 W. Scott Harrington's patients tested positive for hepatitis C, but at this point only the one patient-to-patient case has been directly tied to his dental practice in suburban Tulsa, officials said.
Four cases of HIV were found; the CDC is conducting genetic testing to determine whether those cases are tied to the dental office.
"This is the first documented report of patient-to-patient transmission of hepatitis C virus associated with a dental setting in the United States," state epidemiologist Dr. Kristy Bradley said. "While dental procedures are generally safe, this reinforces the importance of adhering to strict infection control procedures in dental settings."
State health investigators shut down Harrington's dental practice in March -- and asked 7,000 of his patients to be tested for hepatitis and HIV -- after health officials found sterilization and other infractions at his offices.
The Oklahoma Public Health Laboratory completing testing for 4,202 of his patients; an unknown number also sought testing though their private health provider, health officials said.
CNN's Joe Sutton and Jen Pifer Bixler contributed to this report.
™ & © 2013 Cable News Network, Inc., a Time Warner Company. All rights reserved.