Staphylococcus aureus is a major opportunistic pathogen causing a wide range of infections in humans and animals. Methicillin-resistant S. aureus (MRSA) has traditionally been regarded as a strictly human problem, initially confined to the healthcare settings and later a matter of concern in the general community too. All this changed in 2005 with the isolation of a specific MRSA clone, assigned to Clonal Complex (CC)398, from pigs and pig farmers in the Netherlands. These findings triggered worldwide investigation, showing the presence of this livestock-associated (LA)-MRSA clone in a variety of farm animals and in persons in contact with affected animals. Furthermore, the capacity of LA-MRSA CC398 to cause infections in humans and animals has been well documented. Recently, MRSA with a divergent mecA-homologue gene variant has been discovered in bovines and humans. Together, these emerging MRSA strains from animal sources have raised new questions as to their origin and inter-host transmission, as well as raised global concern in both veterinary and human medicine about health risks posed by MRSA prevailing in livestock. In the present work, we aimed to investigate the extent and molecular epidemiology of the LA-MRSA reservoir in animal and human populations, including on livestock farms and in acute-care hospitals in Belgium. As a secondary objective, the presence of methicillin susceptible S. aureus (MSSA) CC398, from which MRSA CC398 could locally emerge by acquisition of the Staphylococal Cassette Chromosome mec (SCCmec) element, was assessed. To this end, we undertook an extensive and systematic cross-sectional survey of S.aureus and MRSA carriage among humans and animals on pig, veal calf, dairy cattle, beef cattle, broiler and horticulture farms. A questionnaire, completed by all farm residents, was used to assess occupational risk factors for human MRSA CC398 carriage. Bacterial genetic characterisation was done by spa typing, SCCmec typing and multi-locus sequence typing (MLST). Antimicrobial ...