TULSA, Okla. (AP) — Health officials said Thursday that thousands of patients of an Oklahoma oral surgeon should undergo testing for HIV and hepatitis after officials looking into the source of a patient's viruses discovered the dentist's instruments weren't being cleaned properly.

The Oklahoma Board of Dentistry said Thursday that state and county health inspectors went to Dr. W. Scott Harrington's practice after a patient with no other known risk factors tested positive for both hepatitis C and the virus that causes AIDS. Inspectors found multiple sterilization issues at Harrington's offices, including cross-contamination of instruments and the use of a separate, rusty, set of instruments for patients who were known to carry infectious diseases, according to a complaint.

Harrington voluntarily closed his practices in Tulsa and suburban Owasso and is cooperating with investigators, said Kaitlin Snider, a spokeswoman for the Tulsa Health Department. He faces a hearing April 19 and could lose his license.

Officials are sending letters to 7,000 people who are known to have been patients of Harrington but noted that they do not have information for patients before 2007.

"It's uncertain how long those practices have been in place," Snider said. "He's been practicing for 36 years."

Phone numbers for Harrington at his home and offices were disconnected Thursday. A message left with Harrington's malpractice attorney in Tulsa, Jim Secrest II, was not immediately returned.

Snider said letters would be sent Friday to the 7,000 patients who went to Harrington's clinics in Tulsa and Owasso since 2007. The letters recommend testing for hepatitis B, hepatitis C and HIV. The agencies say it is rare for infections to spread in occupational settings but that tests are important.

The Dentistry Board complaint says Harrington and his staff told investigators that a "high population of known infectious disease carrier patients" received dental care from him.

A device used to sterilize all instruments wasn't working properly, the complaint said. A test is supposed to performed monthly and sent to a lab to determine that the equipment is successfully sterilizing instruments, but "no such test had ever been performed in the 6 years one dental assistant had been working at the office," the complaint said.

The doctor also apparently used outdated drugs, as one vial found this year had an expiration date of 1993, the complaint said.

Susan Rogers, executive director of the state Board of Dentistry, said that as an oral surgeon, Harrington routinely does invasive procedures that involve "pulling teeth, open wounds, open blood vessels."

"This is an unprecedented event," Rogers said in an interview. "To my knowledge, this has never happened before as far as a public notification of a (hepatitis C) case involving a dental office."

The health departments said hepatitis B, hepatitis C, and HIV are serious medical conditions and infected patients may not have outward symptoms of the disease for many years. "As a precaution, and in order to take appropriate steps to protect their health, it is important for these patients to get tested," their statement said.

Testing will be offered free of charge at the Tulsa Health Department's North Regional Health and Wellness Center.