There is yet no international standard to assess the efficacy of a washer-disinfector.
Every country has its own way of testing and often even several ways, depending by which Professor or Institute the tests are done.
But basically, they all proceed in the same way by artificially contaminating an endoscope. Where they might be different is in :
 the type and the concentration of inoculum : germs and interfering substances (horse serum, human feaces…) ;
the type of endoscope and the channel they contaminate : the more narrow the channel is, the more difficult it is to get rid of the contamination ;
the way of contaminating and sampling : some contaminate and sample all the channels together (like Germande), others (like HIRL) contaminate and sample each channel separately ;
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the sampling liquid used to flush the channels : most of them use a liquid that neutralize the disinfectant (if not, in case the machine does not rinse well, you might sample diluted glutaraldehyde and by the time it gets to the lab… it is always sterile!).
In addition to a neutralizing solution, some use a recovering solution that helps to detach and recover the remaining germs. In any case, the sampling has to be validated, in order to make sure it recovers most of the microorganisms remaining in the channels.
the level of reduction and the number of trials : depending on the type of microorganisms. For bacteria, 5 log reduction is often considered as sufficient. Some ask for a certain number of trials, with all having at least X log reduction, to ensure the reproducibility of the process.
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