To prioritise and optimise risk management and thereby reduce human incidence, qualitative and, preferably, quantitative procedures should be available. They rarely are - partly because some microorganisms are ubiquitous with poorly understood transmission pathways. Some national animal controls scarcely affected food contamination or human incidence. Knowledge of the level and significance of zoonotic agents in food is sometimes limited and minimum ingestion levels for human infection are not fully understood. International travel is constantly increasing.
Bacteria can also adapt to new environments.
Thus, certain Salmonellae have acquired antibiotic resistance and VTEC 0157 seems established in cattle. Where pathogens cannot be easily eliminated, incremental risk reduction should apply generally. The respective responsibilities of food-chain operators must be highlighted. Both logically and empirically, action taken at or near source is often more effective in reducing pathogen levels entering the chain. For brucellosis, affecting both large and small ruminants, livestock controls are essential to reduce the possibility of direct human transmission and indirect contamination from untreated or inadequately treated milk and milk products.