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The improperly cleaned equipment could transmit lingering bacteria and viruses from patient to patient, including tuberculosis and hepatitis C. Every year, more than 15 million people undergo what is known as an endoscopic procedure, an exam by a physician using a tiny camera mounted on a thin, flexible scope. It is a tool that can help in the early detection of colon cancer and other ailments.

A 1995 Food and Drug Administration study that examined endoscopes at 80 US health facilities, for instance, found 38 sites that had endoscopes which were deemed "clean and ready for use," but which were, in fact, "visibly encrusted with debris." While not all residue found in an endoscope is infectious material, a less-than-clean instrument could conceivably transmit disease.

"When scopes are used to look inside of the colon, they pick up things like E. coli or salmonella pseudomonas that might contaminate the scope and give someone a few days of nausea and diarrhea," says Lewis. "In an elderly patient that actually may turn into a fatal infection," he adds.

How Great a Risk?

The chances of an infectious organism being transmitted to a patient by one of these instruments is only one in 1.8 million, according to the American Society for Gastrointestinal Endoscopy.

But David Lewis, a microbiologist with the University of Georgia, told ABCNEWS' Medical Editor Dr. Timothy Johnson on Good Morning America that the risk is much greater. "I've calculated, just based on amount of blood that can leak back out of the scope after it's manually cleaned, that the infection rate may be as high as several patients out of 100," he says. "I think probably the actual infection rate is somewhere in between."

The problem, Lewis says, is that bacteria and viruses are extremely difficult to trace back to an endoscope, even if that was their source.

"We don't have a good tracking system. Patients get endoscopy done, they go home, they're sick, and they go back to their primary care physician, not to their endoscopist. So, rarely does the endoscopist even know that the patient got sick after the procedure was done," he says.

'How Could This Happen?'

In some cases, patients believe that the connection between a procedure and an infection is quite clear.

Eighteen months ago Mary Greene fell ill after undergoing a colonoscopy at the Summit Surgical Center in Voorhees, N.J.. Green says she was shocked to learn recently that at the time of her procedure, the machine used by the center to clean the scopes had been broken.

"I just felt, you know, 'How could this happen?' I didn't find out what happened until I read it in the newspaper on January 23rd [2002], and then I was really upset," she says.

Greene, who recovered after a course of antibiotics, has now joined in a lawsuit that alleges that as many as 1,800 patients at the Summit Center may have been placed at risk of exposure to infectious agents over a 16-month period. Lewis is an expert witness for the plaintiff.

The center has said there is a remote possibility that the machine may have been malfunctioning during a two-week period, and has offered precautionary screening to all patients who were treated during that time.

Difficult to Clean

Dr. Paul Schroy, director of clinical gastroenterology research at Boston Medical Center, believes that when it comes to disinfecting scopes, most endoscopy units are getting the job done.

"It's a highly effective process," he says. "In the cases where disease has been transmitted, scopes were not handled properly."

But according to Lewis, even health facilities that make a serious effort to clean their endoscopes may fall short of this goal.

One reason is that many endoscopes have tiny tubes which are difficult or impossible to clean manually with brushes. Another reason is that the FDA recommended time for immersion in disinfectants is only 45 minutes.

"We're looking at a process that may take an hour and a half to two hours to properly do the procedure between patients," he adds.

According to a 1999 study reported in the journal Gastrointestinal Endoscopy, many scopes are not left in the cleaning solution for the FDA specified 45 minutes.

New Disposable Technology

Dr. Armin Ernst, director of interventional pulmonology at Beth Israel Deaconess Medical Center in Boston, points out that new scope technologies might offer ways of reducing the risk of spreading infections.

"Every time humans are involved, human error is a potential. I think we need to pursue other avenues. For example, disposable guides, disposable sheaths, disposable instruments even, since that will be the ultimate in safety."

Vision Sciences Inc., in Natick Mass., has already developed a disposable sheath. But critics of disposable endoscopic technology argue that such sheaths are difficult to use, and there is no reason to switch to this more costly alternative when no significant risk to patients has been clearly demonstrated.

Even as experts disagree on the actual risk to patients, they all agree that endoscopy is an invaluable medical tool.

"The chance of infection is small. The chance of having a very serious health problem from avoiding endoscopy is quite high," says Lewis.

Johnson suggests patients should be proactive and ask questions.

"Go to the doctor, nurse, and say 'How many minutes do you clean it? What do you do?'" he recommends. "I think in major centers you can have confidence the scopes are cleaned properly all the time. In smaller offices there might be more of a risk — but of course you ask, 'Do you leave it in the cleaning solution for 45 minutes? Do you follow the F.D.A. guidelines?' That will put them on notice."