The updated version of the GUIDELINE OF THE ROBERT KOCH INSTITUTE (RKI): "Hygiene requirements for processing medical devices" calls for clean, residue-free medical devices so that subsequent disinfection or sterilisation steps are not impeded. The cleaning results must be included in quality assurance.
The second version of prEN 15883-1 "Validation of Washer Disinfectors" has just been published. Already in the Introduction, reference is made to the elementary importance of cleaning, which hitherto had only played a subordinate role:
"Verification of cleaning efficacy is a key of establishing satisfactory performance of a washer-disinfector. The current state of knowledge has not permitted development of a single test method. As an interim measure the specification for test methods includes methods previously used in a number of different countries. It remains the intention of technical committee to develop a single test method."
Assessment of cleaning by means of visual inspection
CLEANING is assessed in everyday routine operation by means of visual inspection. This can be easily accomplished in the case of instruments that have no internal lumens. Residues of the heme pigment found in the haemoglobin of the blood can still be easily detected even in quantities as small as 10 µg/cm2. Optical aids can be used to facilitate examination of filigree instruments. But there are also body fluids that contain no pigment and are therefore transparent even in large quantities and cannot be detected.
Narrow-lumened instruments, in addition to other types of instruments, were recently examined in a multi-centre trial. It was revealed that 20 to 50% of the instruments declared as being clean still showed 30-90 µg proteins. For these examinations, the entire instrument was rinsed off in each case with a solution and then the protein content was determined.
Draft standard prEN ISO 15883-1 also calls for VERIFICATION OF THE SPRAY ACTION. This is intended as a means of checking whether in typical machine loads the water jets, or water surge, reach all items to be cleaned as well as the trays and the walls of the chamber. To this effect, Annex B lists various test soils and methods normally used in European countries.
The NATIONAL TEST SOILS listed in Annex B produce different, incomparable results. The test soils are applied manually with a brush to the instruments, chamber walls and inserts. Some soils are composed of water-soluble proteins, others contain starch and the yolk of an egg, and some contain pigments so that they can be detected more easily during visual inspection.
Annex D, table 1,recommends DAILY VISUAL INSPECTION for verification of cleaning efficacy. This reflects the customary practice of subjecting each load to visual inspection.
Testing should be conducted once every three months with one of the test soils. This would mean that the test soil must be prepared and used at least for one processing load. Assessment is to be carried out by means of visual inspection after the cleaning step; there should be no trace of visible residues. This type of test cannot be standardised, nor can it be checked on the basis of quantitative evaluation.
Test Soils and Process Challenge Devices
The national established method for Germany featured in prEN 15883 entails the use of BIOLOGICAL INDICATORS AS PER THE RKI, including screws with semolina or defibrinated sheep blood. The latter are validated process challenge devices (PCDs), which are positioned at locations - deemed to be the most unfavourable by the user - in mesh trays, for example at the centre of rotation of the washing arms or in the corners of the washer-disinfector. Theoretically it is possible to assess removal of the test soil and test microorganisms (Enterococcus faecium ATCC 6057) also by means of visual inspection or quantitatively by microbiological determination of the reduction in the microbial count following the cleaning step. In the German draft, the biological indicators are removed after the programme has completed its entire run. Visual inspection, followed by microbiological evaluation, is carried out on removal. The results of the mechanically removed (washed) and dead test microorganisms are summarised and expressed as a reduction factor.
At this point in time there was no possibility to incorporate new German proposals as test methods into the draft standard.
In December 2001 the draft which is now available has been debated in the European delegation, and will probably be passed at ISO level in spring 2002.
Once prEN 15883-1 has been published as a standard its implementation will be debated within the framework of the quality assurance measures required by the RKI.
For verification of cleaning efficacy in a washer-disinfector, the use of standardised CLEANING INDICATORS, inter alia, which have a defined form and test soil are recommended. Removal of the test soil by the processing procedure can be determined by visual inspection, and possibly also chemically by resorting to quantitative evaluation.
Another verification method entails SEMI-QUANTITATIVE INVESTIGATION of selected instruments or regions thereof for protein residues. To this effect, the colorimetric biuret method or a modified biuret method can also be used on site.
Whereas more comprehensive investigations can also be carried out on site for type tests and performance qualification tests conducted within the framework of validation, it should be possible for the operating personnel to easily implement and evaluate METHODS FOR ROUTINE CHECKS. In line with the demands of quality assurance, the operator is required to compile written working instructions documenting the processing steps. To this effect, the control measures and control intervals must be specified. The results must be documented.