title: Risk factors for surgical site infection following laparotomy: Effect of season and perioperative variables and reporting of bacterial isolates in 287 horses.
abstract: BACKGROUND
  Surgical site infection (SSI) is an important cause of post operative morbidity following laparotomy.
  
  
  OBJECTIVE
  To investigate risk factors for SSI, including effect of season and surgery performed outside normal working hours, and to report bacterial isolates and antimicrobial resistance patterns.
  
  
  METHODS
  Retrospective cohort study.
  
  
  METHODS
  Data were obtained from horses that had undergone exploratory laparotomy over a 3-year period (2010-2013) in a UK hospital population. SSI was defined as any purulent or serous discharge from the laparotomy incision of >24 h duration that developed during hospitalisation. Multivariable logistic regression was used to identify associations between pre-, intra- and post operative variables and altered likelihood of SSI.
  
  
  RESULTS
  Surgical site infection developed in 73/287 (25.4%) horses during hospitalisation. Horses of greater bodyweight (odds ratio [OR] 1.002, 95% confidence interval [CI] 1.0002-1.005, P = 0.03), increased packed cell volume (≥48%) on admission (OR 3.03, 95% CI 1.32-6.94, P = 0.01), small intestinal resection (OR 2.27, 95% CI 1.15-4.46, P = 0.02) and post operative colic (OR 2.86, 95% CI 1.41-5.79, P = 0.003) were significantly associated with increased likelihood of SSI in a multivariable model. SSI was also significantly more likely to occur during winter (OR 3.84, 95% CI 1.38-10.70, P = 0.01) and summer (OR 5.63, 95% CI 2.07-15.3, P = 0.001) months in the model. Three-layer closure of the incision was protective (OR 0.31, 95% CI 0.16-0.58, P<0.001) compared to 2-layer closure. There was no effect of surgery being performed outside normal working hours (P = 0.5). The most common bacterial isolates were Escherichia coli (59.5%), Enterococcus spp. (42.4%) and Staphylococcus spp. (25.4%). Penicillin resistant isolates accounted for 92% (96/104) of isolates while 18% (21/119) of isolates were gentamicin resistant.
  
  
  CONCLUSIONS
  Laparotomy during winter and summer months was associated with increased likelihood of SSI but there was no effect of surgery performed outside normal working hours. This information assists in identifying horses at high risk of SSI and informing development of preventive strategies.
authors.affiliation: Philip Leverhulme Equine Hospital, School of Veterinary Science/Institute of Infection and Global Health, Leahurst Campus, University of Liverpool, Neston, Wirral, UK.
authors.forename: C M
authors.initials: CM
authors.lastname: Isgren
authors.affiliation: Philip Leverhulme Equine Hospital, School of Veterinary Science/Institute of Infection and Global Health, Leahurst Campus, University of Liverpool, Neston, Wirral, UK.|Department of Surgery, Faculty of Veterinary Medicine, Zagazig University, Zakazik, Egypt.
authors.forename: S E
authors.initials: SE
authors.lastname: Salem
authors.affiliation: Philip Leverhulme Equine Hospital, School of Veterinary Science/Institute of Infection and Global Health, Leahurst Campus, University of Liverpool, Neston, Wirral, UK.
authors.forename: D C
authors.initials: DC
authors.lastname: Archer
authors.affiliation: Philip Leverhulme Equine Hospital, School of Veterinary Science/Institute of Infection and Global Health, Leahurst Campus, University of Liverpool, Neston, Wirral, UK.
authors.forename: F C F
authors.initials: FC
authors.lastname: Worsman
authors.affiliation: Philip Leverhulme Equine Hospital, School of Veterinary Science/Institute of Infection and Global Health, Leahurst Campus, University of Liverpool, Neston, Wirral, UK.
authors.forename: N B
authors.initials: NB
authors.lastname: Townsend
mesh_terms: D000818:Animals; D001419:Bacteria / Q000145:classification*; D001424:Bacterial Infections / Q000382:microbiology / Q000662:veterinary*; D015331:Cohort Studies; D006734:Horse Diseases; D006736:Horses; D007813:Laparotomy / Q000009:adverse effects / Q000662:veterinary*; D059035:Perioperative Period; D012189:Retrospective Studies; D012307:Risk Factors; D012621:Seasons; D013530:Surgical Wound Infection / Q000209:etiology / Q000662:veterinary*
keywords: bacterial isolates; colic; exploratory laparotomy; horse; season; surgical site infection