UVC Based Disinfection Process for Endocavitary Ultrasound Probes

Background: Ultrasound-based diagnostic imaging techniques are widely used in medicine. Endocavitary probes (without a probe cover) contact mucous membranes and are considered to be semicritical devices. Therefore they should be submitted between patients to a disinfection process eliminating all microorganisms in or on the instrument except small numbers of bacterial spores (i.e. high level disinfection {HLD} according to US CDC guideline and intermediary level of disinfection according to French guideline). In a recent document, experts from the French minister of health considered that the use of a probe cover/condom changes the risk category and allows the user to apply a lower level of disinfection. On the opposite, US experts think that condoms/probe covers can fail and that cleaning followed by HLD is required even if probe covers have been used.Chemical disinfection is the most commonly recommended procedure for these probes but their efficacy, toxicity and compatibility have been questioned.

Objective: Germitec has developed a new disinfection process (AS 1) based on UV-C radiation for the disinfection of external and endocavitary ultrasound probes. The objective of this study was to evaluate the efficacy of this alternative procedure according to a test method based on carrier tests currently used in Europe for the evaluation of chemical disinfectants.

Methods: 4 cm² predefined surface of a frosted glass carrier were inoculated with 50 µl of a test suspension containing about 3.0 x 10⁵ CFU/carrier and 10% of bovine serum albumin. Contaminated carriers are maintained at room temperature until complete drying and submitted to UVC treatment in the AS 1 chamber. After treatment, glass carriers are transferred into 10 ml of recovery solution and 1 ml of glass beads and the number of viable microorganisms is determined after tenfold serial dilutions, using the pour plate technique. After incubation, plates are counted and results are expressed as a number of colony forming units per carrier.

Results: results obtained demonstrate a 4.0-log₁₀ reduction for Mycobacterium avium CIP 105415 and Mycobacterium terrae CIP 104321 within 60 seconds of treatment and within 180 seconds for Aspergillus niger IP 1431.83 spores. After a 60 seconds exposure time in the AS 1 a 5.0-log₁₀ reduction was obtained for glass carriers contaminated with Escherichia coli CIP 54127.

Conclusions: The efficacy levels reached are comparable to log reductions required in Europe for a liquid chemical disinfectant used on semicritical devices. Nevertheless, according to others standard like ISO 15883-4 or AOAC, higher efficacy levels should be reached (i.e. 5.0- to 6.0-log₁₀ reduction on Mycobacterium sp.). This study demonstrates the need to define the antimicrobial efficacy levels required for such non-chemical disinfection processes used on simple medical devices and for which the use of probe covers/condom and cleaning before disinfection is always recommended.