title: Longitudinal study on transmission of MRSA CC398 within pig herds.
abstract: ABSBACKGROUND: Since the detection of MRSA CC398 in pigs in 2004, it has emerged in livestock worldwide. MRSA CC398 has been found in people in contact with livestock and thus has become a public health issue. Data from a large-scale longitudinal study in two Danish and four Dutch pig herds were used to quantify MRSA CC398 transmission rates within pig herds and to identify factors affecting transmission between pigs.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Quantitative Veterinary Epidemiology Group, Wageningen Institute of Animal Sciences, Wageningen University, P,O, Box 338, Wageningen, 6700 AH, The Netherlands. e.m.broens@uu.nl
authors.forename: Els M
authors.initials: EM
authors.lastname: Broens
authors.forename: Carmen
authors.initials: C
authors.lastname: Espinosa-Gongora
authors.forename: Elisabeth A M
authors.initials: EA
authors.lastname: Graat
authors.forename: Nadia
authors.initials: N
authors.lastname: Vendrig
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Van Der Wolf
authors.forename: Luca
authors.initials: L
authors.lastname: Guardabassi
authors.forename: Patrick
authors.initials: P
authors.lastname: Butaye
authors.forename: Jens Peter
authors.initials: JP
authors.lastname: Nielsen
authors.forename: Mart C M
authors.initials: MC
authors.lastname: De Jong
authors.forename: Arjen W
authors.initials: AW
authors.lastname: Van De Giessen
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D003718:Denmark / Q000453:epidemiology; D004783:Environmental Microbiology; D006799:Housing, Animal; D055624:Methicillin-Resistant Staphylococcus aureus / Q000145:classification*; D009426:Netherlands / Q000453:epidemiology; D013203:Staphylococcal Infections / Q000453:epidemiology / Q000382:microbiology / Q000635:transmission / Q000662:veterinary*; D013552:Swine; D013553:Swine Diseases / Q000453:epidemiology / Q000382:microbiology* / Q000635:transmission; D013997:Time Factors
chemical_list: D000900:Anti-Bacterial Agents