MURFREESBORO, Tenn. -- The colonoscopy scare at the V.A. Hospital in Murfreesboro has gone from what was called an "isolated incident" to a nationwide alert.

Related: Video | Colonoscopy Patient Letter (PDF)

Channel 4 first broke the story on New Years Eve.

A week later, the V.A. Hospital admitted someone put the wrong valve on a colonoscopy machine, possibly exposing at least two people to contaminated fluids.

Now it has come out that the improper valve could have been used for more than five years, along with faulty cleaning procedures, and 6,400 veterans could be at risk.

"Any concern with this procedure has been addressed and, we believe, was limited to a single occurrence," Juan Morales said a month ago, when the director of the Tennessee Valley Healthcare System admitted the wrong valve was placed on a colonoscopy machine at the York V.A. Hospital.

What was originally thought to have affected two patients has now ballooned into 6,400 patients possibly at risk for infection.

Staff at York can't recall when the wrong valve was first put on a colonoscopy machine.

"It was introduced into the facility when the Olympus washing scopes were first brought to the facility on or about April 23, 2003," said William Duncan, M.D., quality assurance director.

The wrong valve may have been used from April 23, 2003, to Dec. 1, 2008, allowing toxic body fluids to move two ways instead of only one.

That isn't the only thing that has gone wrong.

"There were a number of reprocessing -- and by reprocessing, I mean use or reuse before appropriate disinfection," said Duncan.

V.A. officials failed to mention that last month, even though a patient safety alert was issued two weeks earlier, acknowledging that tubing wasn't properly being cleaned between procedures.

The head of quality assurance with the Veterans Health Administration assures all veterans they sincerely regret this mistake.

"We want our patients to have confidence in us," Duncan said. "We're doing the right thing. This is not a pleasant process for us or for our patients to go through."

The 6,400 patients possibly affected have not yet been notified.

A letter that will soon be mailed out states that everyone will be offered free blood testing.

This problem originally started in Murfreesboro, but is now prompting a nationwide special training campaign happening next month at every V.A. facility in the country.

If you've had a colonoscopy at the York V.A. Center between April 2003 and last December, there is a dedicated phone line available to answer your questions. You can call 1-877-345-8555 Monday to Friday, 8 a.m. to 7 p.m. (CST).