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.

Radiographic identification of the equine ventral conchal bulla

Involvement of the ventral conchal sinus (VCS) is an important diagnostic and prognostic feature in cases of the equine sinus disease. The authors aimed to ascertain if the caudo-dorsal extension of the VCS, the ventral conchal bulla (VCB) is identifiable on plain radiographs of cadaver skulls without sinus disease. Bilateral frontonasal sinus flaps were made in 10 equine cadaver skulls. Plain lateral, lateral oblique and dorso-ventral radiographs were then obtained followed by the same views taken with stainless steel wire outlining the caudal border of the VCB. Plain radiographs were randomised and blindly evaluated by two observers who marked where they believed the VCB to be positioned. This was then correlated with the true position of the VCB using radiographs with wires in place. The ease of identification of the VCB was classified as 'easy' or 'difficult'. The VCB was correctly identified in 70 per cent of lateral radiographs, but only 45 per cent of lateral oblique radiographs and 17 per cent of dorso-ventral radiographs. If a clinician was confident that he or she could identify the VCB, they were usually correct. Conversely if the clinician judged VCB identification as 'difficult', they usually identified it incorrectly. In the authors' clinical experience, the VCB of horses with sinusitis involving this compartment is more radiologically evident than in clinically normal horses. Knowledge of the normal radiographic anatomy of this structure should aid clinicians in identifying horses with sinusitis affecting the VCS.

Historical and clinical features of 200 cases of equine sinus disease

The historical and clinical findings in 200 referred cases of equine sinus disease were reviewed retrospectively. Univariable and multivariable analyses were performed to detect significant differences in historical or clinical features between various categories of sinus disease. The causes of sinus disease were classified as subacute primary (less than two months duration) (n=52), chronic primary (more than two months duration) (n=37), dental (n=40), sinus cyst (n=26), traumatic (n=13) or mycotic sinusitis (n=7), sinus neoplasia (n=10), dental-related oromaxillary fistula (n=8) and intrasinus progressive ethmoid haematoma (n=7). The majority of sinus disorders were of chronic duration at the time of referral and most (including 97 per cent of chronic primary sinusitis cases) had not responded to previous antibiotic therapy and/or sinus lavage in some cases. Clinical signs included unilateral nasal discharge in most cases, including purulent or mucopurulent discharge in all horses with primary, dental and mycotic sinusitis. Haemorrhagic nasal discharge was a feature of traumatic sinusitis and intrasinus progressive ethmoid haematomas. Firm facial swellings and nasal airflow obstruction were features of sinus cysts and neoplasms. Ipsilateral lymphadenitis was a more prominent feature of sinus disease with active infections such as primary, dental or mycotic sinusitis.