title: Livestock-associated methicillin and multidrug resistant Staphylococcus aureus is present among industrial, not antibiotic-free livestock operation workers in North Carolina.
abstract: OBJECTIVE
  Administration of antibiotics to food animals may select for drug-resistant pathogens of clinical significance, such as methicillin-resistant Staphylococcus aureus (MRSA). In the United States, studies have examined prevalence of MRSA carriage among individuals exposed to livestock, but prevalence of multidrug-resistant S. aureus (MDRSA) carriage and the association with livestock raised with versus without antibiotic selective pressure remains unclear. We aimed to examine prevalence, antibiotic susceptibility, and molecular characteristics of S. aureus among industrial livestock operation (ILO) and antibiotic-free livestock operation (AFLO) workers and household members in North Carolina.
  
  
  METHODS
  Participants in this cross-sectional study were interviewed and provided a nasal swab for S. aureus analysis. Resulting S. aureus isolates were assessed for antibiotic susceptibility, multi-locus sequence type, and absence of the scn gene (a marker of livestock association).
  
  
  RESULTS
  Among 99 ILO and 105 AFLO participants, S. aureus nasal carriage prevalence was 41% and 40%, respectively. Among ILO and AFLO S. aureus carriers, MRSA was detected in 7% (3/41) and 7% (3/42), respectively. Thirty seven percent of 41 ILO versus 19% of 42 AFLO S. aureus-positive participants carried MDRSA. S. aureus clonal complex (CC) 398 was observed only among workers and predominated among ILO (13/34) compared with AFLO (1/35) S. aureus-positive workers. Only ILO workers carried scn-negative MRSA CC398 (2/34) and scn-negative MDRSA CC398 (6/34), and all of these isolates were tetracycline resistant.
  
  
  CONCLUSIONS
  Despite similar S. aureus and MRSA prevalence among ILO and AFLO-exposed individuals, livestock-associated MRSA and MDRSA (tetracycline-resistant, CC398, scn-negative) were only present among ILO-exposed individuals. These findings support growing concern about antibiotics use and confinement in livestock production, raising questions about the potential for occupational exposure to an opportunistic and drug-resistant pathogen, which in other settings including hospitals and the community is of broad public health importance.
authors.affiliation: Department of Epidemiology, University of North Carolina, Chapel Hill, North Carolina, USA.
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Rinsky
authors.forename: Maya
authors.initials: M
authors.lastname: Nadimpalli
authors.forename: Steve
authors.initials: S
authors.lastname: Wing
authors.forename: Devon
authors.initials: D
authors.lastname: Hall
authors.forename: Dothula
authors.initials: D
authors.lastname: Baron
authors.forename: Lance B
authors.initials: LB
authors.lastname: Price
authors.forename: Jesper
authors.initials: J
authors.lastname: Larsen
authors.forename: Marc
authors.initials: M
authors.lastname: Stegger
authors.forename: Jill
authors.initials: J
authors.lastname: Stewart
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Heaney
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D002353:Carrier State / Q000453:epidemiology* / Q000382:microbiology / Q000635:transmission; D003430:Cross-Sectional Studies; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects*; D005260:Female; D006801:Humans; D058751:Livestock / Q000382:microbiology*; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus / Q000235:genetics / Q000302:isolation & purification*; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D009657:North Carolina / Q000453:epidemiology; D009666:Nose / Q000382:microbiology; D011200:Poultry / Q000382:microbiology; D015995:Prevalence; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology / Q000635:transmission; D013552:Swine / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents