Longitudinal study on transmission of MRSA CC398 within pig herds

Sows and their offspring were sampled at varying intervals during a production cycle. Overall MRSA prevalence of sows increased from 33% before farrowing to 77% before weaning. Overall MRSA prevalence of piglets was？>？60% during the entire study period. The recurrent finding of MRSA in the majority of individuals indicates true colonization or might be the result of contamination. Transmission rates were estimated using a Susceptible-Infectious-Susceptible (SIS-)model, which resulted in values of the reproduction ratio (R0) varying from 0.24 to 8.08. Transmission rates were higher in pigs treated with tetracyclins and β-lactams compared to untreated pigs implying a selective advantage of MRSA CC398 when these antimicrobials are used. Furthermore, transmission rates were higher in pre-weaning pigs compared to post-weaning pigs which might be explained by an age-related susceptibility or the presence of the sow as a primary source of MRSA CC398. Finally, transmission rates increased with the relative increase of the infection pressure within the pen compared to the total infection pressure, implying that within-pen transmission is a more important route compared to between-pen transmission and transmission through environmental exposure.Our results indicate that MRSA CC398 is able to spread and persist in pig herds, resulting in an endemic situation. Transmission rates are affected by the use of selective antimicrobials and by the age of pigs.In 2004, a distinct clone of methicillin resistant Staphylococcus aureus (MRSA CC398), referred to as livestock-associated (LA), was found in pigs and in people in contact with pigs [1]. Various observational studies have detected LA-MRSA in pig and other livestock herds worldwide, and risk factors for herds to be MRSA positive have been identified [2-7].Antimicrobial resistant microorganisms in livestock become a public health issue when resistant organisms or resistance genes can transfer from livestock to humans. The role of a