(CNN) -- Some 7,000 patients of a Tulsa, Oklahoma, dental practice were being notified they could have been exposed to HIV and hepatitis over the past six years, health authorities said Thursday.
Dentist W. Scott Harrington voluntarily stopped practicing when the joint investigation by the Tulsa Health Department and the Oklahoma State Department of Health began, the Tulsa agency said in a statement. "The dentist is cooperating with investigators through his attorney," the department said.
According to the State Board of Dentistry, the investigation into Harrington's practice found "numerous violations of health and safety laws and major violations of the State Dental Act," the health department said.
While the statement did not elaborate, the department said investigators with the state dental board "have been assisted by agents from the Oklahoma Bureau of Narcotics and the United States Drug Enforcement Administration concerning the maintenance, control and use of drugs on the premises."
The investigation, it said, is "multifaceted and ongoing."
Patients who have seen Harrington since 2007 will be notified by letter. It is recommended they be tested for hepatitis B, hepatitis C and HIV, the health department said. Harrington worked in the Tulsa suburb of Owasso.
"Hepatitis B, hepatitis C and HIV are serious medical conditions, and infected patients may not have outward symptoms of the disease for many years," the health department said.
"As a precaution, and in order to take appropriate steps to protect their health, it is important for these patients to get tested. It should be noted that transmission in this type of occupational setting is rare."
Callers to Harrington's office heard a recording stating the office was currently closed. CNN spoke to an emergency page representative, who said she believed the closure was temporary.
The page representative said Harrington was not available unless a caller had a dental emergency.
Patient information is available only from the past seven years, the department said. Those who saw Harrington before 2007 may not receive a letter.
Testing will be done free of charge at the health department starting Saturday and resuming on Monday, the statement said. A hotline has been set up for people with questions about the notifications.
CNN's Joe Sutton contributed to this report.