Professor Alan Reilly:

One could detect traces with a kitchen knife. If one sliced beef with a knife and then one sliced pork with it, one could possibly detect some cells. However, we are discussing commercial conditions in which tens of tonnes of meat go down a processing line and people clean out the line afterwards. However, what degree of cleaning is necessary? How likely is a person to leave behind traces? Any system that is eventually adopted will have to have built in this type of testing within each processing facility, probably once or twice per year. After cleaning down, an operator must consider the traces left behind such that it can give guarantees to its customers that there will be no such crossover contamination.

To answer Deputy McNamara's question, if after slicing meat I gave the knife a good clean I would probably get rid of any contamination, but if I only gave it a quick wipe it may be different. Perhaps under commercial or industrial conditions one might not employ the same strict hygiene that one would have in one's own kitchen.