Dose-Response Relationship between Antimicrobial Drugs and Livestock-Associated MRSA in Pig Farming 1

The farming community can be a vehicle for introduction of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) in hospitals. During 2011–2013, an 18-month longitudinal study aimed at reducing the preva lence of LA-MRSA was conducted on 36 pig farms in the Netherlands. Evaluations every 6 months showed a slight decrease in MRSA prevalence in animals and a stable prev alence in farmers and family members. Antimicrobial use, expressed as defined daily dosages per animal per year, decreased 44% during the study period and was associated with declining MRSA prevalence in pigs. MRSA carriage in animals was substantially higher at farms using cepha -losporins. Antimicrobial use remained strongly associated with LA-MRSA in humans regardless of the level of animal contact. A risk factor analysis outlined potential future in terventions for LA-MRSA control. These results should en courage animal and public health authorities to maintain their efforts in reducing antimicrobial use in livestock and ask for future controlled intervention studies.