Key words: endoscope sheath, virus, barrier, laboratory test, standards
Sheaths are increasingly used on endoscopes to reduce the need for high-level sterilization between uses. There is a need for a meaningful test of the barrier function of these sheaths.
Combined efforts of scientists in OST (DLS and DPS) and ODE (ENT Branch) devised three methods that could determine some aspect of the barrier function of the sheaths used to cover ENT endoscopes. One method, the air deflation test, inflates two sheaths to a certain pressure and then compares any difference in pressure between the test sheath and one known to be intact. The first of two complementary virus barrier test methods challenges the sheath with a saline solution containing a challenge virus, bacteriophage (X174, on the outside, with virus penetration determined by rinsing the inside of the sheath and the endoscope and assaying for the virus. The other virus barrier test method challenges the sheath from the inside, with penetration of virus determined by assaying a collection solution into which the endoscope/sheath combination had been submerged. The abilities of these test methods to detect sheaths with laser-drilled holes were compared. The air deflation test was evaluated in DPS and was found to detect holes as small as 5 microns. This test has potential use as a non-destructive, in-line quality assurance test. The virus challenge tests were conducted in the Microbiology Branch at WEAC. The outside challenge virus barrier test method could reliably detect virus penetration through holes of 30 microns in diameter and could not detect 5 micron holes at all, while the second method could reliably detect holes of 5 microns and larger. Both virus penetration tests were destructive in that it was impractical to sterilize the sheaths for reuse. In addition, the presence of air bubbles during initial submersion when the endoscope was being inserted into the sheath allowed detection and location of holes as small as 5 microns, suggesting a possible second non-destructive quality assurance test. The low amounts (<10-2 L) of virus penetration during the outside challenge virus barrier test indicate that endoscope contamination was low even for relatively large holes (30 microns). It was concluded that the detection of 5 micron holes should be adequate and that the air deflation test and the bubble test could both serve as quality assurance tests and, possibly, as tests to qualify products of the same material as adequate barriers to virus passage. One or more of these methods will be presented as potential standards.