As you rightly to point out, it is very complex. We have to talk about the food chain, but let us look at the route which is the primary source of pathogen ingress into the food chain. To take the case of poultry, one of the issues is that some countries, including America, they have intensive rearing of poultry; they also have cattle feed lots, where animals are raised and fed in a dense community. In the UK and Europe, our husbandry standards appear to be better, poultry are reared in less intensive conditions and we do not have cattle in feed lots like the Americans do, so the animals have more space, they appear to be healthier and, from what we have seen so far, they have reduced numbers of pathogens at that stage.
Of course, you are quite correct that every step in the food chain is a potential source of contamination. If we use lorries, provided that those lorries are properly cleaned and decontaminated, that should not be an issue. When food is produced for restaurants, if the staff adopt good hygiene, they should not transmit pathogens to the customers—that has been well documented. The supermarkets are very responsible; they have a reputation to maintain—they do not want to be seen as the supermarket that poisons their customers—so they maintain very high standards.