A multi-centre cohort study investigating the outcome of synovial contamination or sepsis of the calcaneal bursae in horses treated by endoscopic lavage and debridement.

BACKGROUND: Previous studies investigating factors associated with survival following endoscopic treatment of contamination/sepsis of the calcaneal bursa are limited. OBJECTIVES: To investigate the factors associated with survival in horses with contamination/sepsis of the calcaneal bursae treated endoscopically and to describe the bacterial isolates involved in the synovial infections. STUDY DESIGN: Retrospective analysis of clinical records. METHODS: Medical records from 128 horses with contamination/sepsis of the calcaneal bursae treated by endoscopic lavage at seven equine hospitals were reviewed. A follow-up questionnaire was used to determine survival and return to athletic performance. Descriptive statistics and Cox proportional hazards survival models were used to determine factors associated with survival. RESULTS: Horses underwent one (n = 107), two (n = 19), or three (n = 2) surgeries. Survival to hospital discharge was 84.4%. Univariable survival analysis revealed that administration of systemic antimicrobials prior to referral was associated with reduced mortality (hazard ratio, [HR] 0.41, 95% CI 0.18-0.91, P = 0.03). Increased mortality was associated with bone fracture/osteomyelitis (HR 2.43, 95% CI 1.12-5.26, P = 0.03), tendon involvement (≥30% cross sectional area) (HR 3.78 95% CI 1.78-8.04, P = 0.001), duration of general anaesthesia (HR 1.01, 95% CI 1.00-1.02, P = 0.04), post-operative synoviocentesis (HR 3.18, 95% CI 1.36-7.43, P = 0.006) and post-operative wound dehiscence (HR 2.5, 95% CI 1.08-5.65, P = 0.04). Multivariable Cox proportional hazards model revealed reduced mortality after systemic antimicrobial administration prior to referral (HR 0.25, 95% CI 0.11-0.60, P = 0.002) and increased mortality with tendinous involvement (≥30% cross-sectional area) (HR 7.92, 95% CI 3.31-19.92, P<0.001). At follow-up (median 30 months, range 0.25-13 years, n = 70) 87.1% horses were alive, 7.1% had been euthanised due to the calcaneal injury and 5.7% had been euthanised for unrelated reasons. From 57 horses with athletic performance follow-up, 91.2% returned to the same/higher level of exercise, 5.3% to a lower level and 3.5% were retired due to persistent lameness of the affected limb. MAIN LIMITATIONS: Retrospective study and incomplete follow-up. CONCLUSION: Endoscopic treatment of contamination/sepsis of the calcaneal bursae has an 84% survival rate to hospital discharge. Tendinous involvement reduced survival whilst systemic antimicrobials administration prior to referral improved survival.

Emergence of carriage of CTX-M-15 in faecal Escherichia coli in horses at an equine hospital in the UK; increasing prevalence over a decade (2008-2017).

BACKGROUND: This study investigated changes over time in the epidemiology of extended-spectrum ß-lactamase (ESBL) producing Escherichia coli within a single equine referral hospital in the UK. Faecal samples were collected from hospitalised horses in 2008 and 2017, processed using selective media and standard susceptibility laboratory methods. A novel real-time PCR with high resolution melt analysis was used to distinguish blaCTX-M-1 and blaCTX-M-15 within CTX-M-1 group. RESULTS: In 2008, 457 faecal samples from 103 horses were collected, with ESBL-producing E. coli identified in 131 samples (28.7, 95% CI 24.6-33.1). In 2017, 314 faecal samples were collected from 74 horses with ESBL-producing E. coli identified in 157 samples (50.0, 95% CI 44.5-55.5). There were 135 and 187 non-duplicate ESBL-producing isolates from 2008 and 2017, respectively. In 2008, 12.6% of isolates belonged to CTX-M-1 group, all carrying blaCTX-M-1, whilst in 2017, 94.1% of isolates were CTX-M-1 group positive and of these 39.2 and 60.8% of isolates carried blaCTX-M-1 and blaCTX-M-15, respectively. In addition, the prevalence of doxycycline, gentamicin and 3rd generation cephalosporin resistance increased significantly from 2008 to 2017 while a decreased prevalence of phenotypic resistance to potentiated sulphonamides was observed. CONCLUSIONS: The real-time PCR proved a reliable and high throughput method to distinguish between blaCTX-M-1 and blaCTX-M-15. Furthermore, its use in this study demonstrated the emergence of faecal carriage of CTX-M-15 in hospitalised horses, with an increase in prevalence of ESBL-producing E. coli as well as increased antimicrobial resistance to frequently used antimicrobials.

Sequential bacterial sampling of the midline incision in horses undergoing exploratory laparotomy.

BACKGROUND: There is limited information about bacterial isolates that are present on the equine midline incision during and following exploratory laparotomy. OBJECTIVES: To investigate the bacterial species cultured from the ventral midline pre-, intra- and post- laparotomy, whether particular bacterial isolates are associated with the development of surgical site infections (SSIs) and to report the antimicrobial resistance phenotypes of these isolates. STUDY DESIGN: Prospective cohort study. METHODS: The ventral midline of 31 horses undergoing exploratory laparotomy was sampled for bacterial culture at set time-points pre, intra and post-operatively. Inclusion criteria were that horses must have undergone exploratory laparotomy within 90 min of the initial colic examination upon hospital admission and must not have been placed in a stable prior to surgery. SSI was defined as any purulent or serous discharge from the laparotomy incision of >24 h duration. RESULTS: Seven horses (22.6%) developed a SSI. None of the variables tested were associated with the altered risk of SSI. The prevalence of a positive bacterial culture from the incision increased progressively over time and a variety of bacteria were isolated. A positive intra-operative culture was not a predictor of SSI; and when a SSI did occur, it was due to a different bacterial isolate. MRSA and ESBL-producers were identified in the post-operative period in one and four different horses respectively, but none of these developed a SSI. MAIN LIMITATIONS: Sampling was limited to hospitalisation and no culture results were available for horses developing SSI following hospital discharge. CONCLUSIONS: A variety of bacterial species may be isolated from equine laparotomy incisions peri-operatively without development of SSI. SSI does not appear to be solely related to bacterial contamination of the incision peri-operatively and other mechanisms such as bacteraemia merit further investigation.

Risk factors for surgical site infection following laparotomy: Effect of season and perioperative variables and reporting of bacterial isolates in 287 horses.

REASONS FOR PERFORMING STUDY: Surgical site infection (SSI) is an important cause of post operative morbidity following laparotomy. OBJECTIVES: 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. STUDY DESIGN: 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.