(CNN)- About 7,000 patients who visited a suburban Tulsa, Oklahoma, dentist in the past six years may have been exposed to HIV and hepatitis, health investigators say.
Investigators were left grasping for words to describe what they found inside W. Scott Harrison's dental practice: assistants doing techniques that only a dentist should, and sterilization procedures and needles that were handled improperly.
"I will tell you that when ... we left, we were just physically kind of sick," said Susan Rogers, executive director of the Oklahoma Board of Dentistry. "I mean, that's how bad (it was), and I've seen a lot of bad stuff over the years."
The state health department will offer free HIV and hepatitis testing to the thousands of patients who sat in Harrington's chairs.
Joyce Baylor, who said she was Harrington's patient in the past, said she heard about the health risk from a news report
Baylor said she has not yet received a letter from health officials but she was going to see her doctor next week.
"The (dental) office was clean," Baylor said. "I had no idea that things weren't what they should have been."
Harrington also allowed "unauthorized, unlicensed" employees to perform intravenous sedation of patients, Rogers said.
"That is completely unacceptable and illegal in Oklahoma," she said.
Investigators do not know if that practice led to infections in any patients of Harrington, who voluntarily stopped practicing after a joint investigation by city and state health departments uncovered numerous violations.
Harrington's office was a "perfect storm" for infections, Rogers said.
The state health department is contacting about 7,000 patients seen by Harrington since 2007 to urge them to be tested for hepatitis B, hepatitis C and HIV.
Harrington, 64, is a veteran oral surgeon who started practicing more than 35 years ago. He worked in the Tulsa suburb of Owasso.
The investigation began after the health department alerted the dentistry board to a potential hepatitis C infection from Harrington's office.
The outward cleanliness of the dentist's office belied the mess that was behind the cabinets, Rogers said.
"Some of the things we found were just absolutely incredible," she said. "It's just basic universal precautions for blood-borne pathogens that they were just not following regular protocols" for.
Rogers said Harrington told investigators that he had a higher population of HIV and hepatitis patients. That compounded the infection risks, Rogers said.
He would accept Medicaid for oral surgery, which often meant treating lower-income people who popped up at emergency rooms and were transferred to him to do extractions and other procedures, she said.
Many of these procedures were invasive and exposed patients' blood, tissue and bones, and investigators discovered that these procedures were being carried out in an unsanitary environment.
"The instruments that came out of the autoclave were horrible," Rogers said, referring to a device used to sterilize tools. "I wouldn't let my nephews play with them out in the dirt. I mean, they were horrible. They had rust on them."
The 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.
"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."