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Randomized, controlled clinical trial to assess the effect of antimicrobial-impregnated suture on the incidence of surgical site infections in dogs and cats

Kelley M. Thieman Mankin1Department of Small Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843.

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Noah D. Cohen2Department of Large Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843.

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Abstract

OBJECTIVE

To evaluate the prophylactic efficacy of triclosan-coated (TC) suture in preventing surgical site infections (SSIs) in dogs and cats undergoing surgical procedures.

ANIMALS

862 animals (794 dogs and 68 cats).

PROCEDURES

Incidences of SSI of surgical wounds closed with TC suture and surgical wounds closed with non-TC suture occurring between the time of surgery and 1 month postoperatively were compared. Animals were randomly assigned to TC or non-TC suture groups. When TC suture was assigned, all suture available as TC material was used rather than non-TC suture. Presence of an SSI was determined by an owner questionnaire or direct examination.

RESULTS

Overall, 50 of 862 (5.8%) animals developed SSIs. Incidence of SSI was 6% (24/428) in the non-TC suture group and 6% (26/434) in the TC suture group. No significant difference was found in the incidence of SSI between groups. No significant difference was detected in the incidence of incisional problems (eg, redness, dehiscence, and seroma formation) between animals in which TC suture was used and those in which non-TC suture was used. On multivariable analysis, other factors were associated with increased SSI rates, including an incision length > 10 cm, surgery performed by the soft tissue surgery department, and anesthesia duration of > 240 minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

No significant difference in incidence of SSI was detected between animals undergoing surgical procedures performed with non-TC versus TC suture.

Abstract

OBJECTIVE

To evaluate the prophylactic efficacy of triclosan-coated (TC) suture in preventing surgical site infections (SSIs) in dogs and cats undergoing surgical procedures.

ANIMALS

862 animals (794 dogs and 68 cats).

PROCEDURES

Incidences of SSI of surgical wounds closed with TC suture and surgical wounds closed with non-TC suture occurring between the time of surgery and 1 month postoperatively were compared. Animals were randomly assigned to TC or non-TC suture groups. When TC suture was assigned, all suture available as TC material was used rather than non-TC suture. Presence of an SSI was determined by an owner questionnaire or direct examination.

RESULTS

Overall, 50 of 862 (5.8%) animals developed SSIs. Incidence of SSI was 6% (24/428) in the non-TC suture group and 6% (26/434) in the TC suture group. No significant difference was found in the incidence of SSI between groups. No significant difference was detected in the incidence of incisional problems (eg, redness, dehiscence, and seroma formation) between animals in which TC suture was used and those in which non-TC suture was used. On multivariable analysis, other factors were associated with increased SSI rates, including an incision length > 10 cm, surgery performed by the soft tissue surgery department, and anesthesia duration of > 240 minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

No significant difference in incidence of SSI was detected between animals undergoing surgical procedures performed with non-TC versus TC suture.

Surgical site infections are an important cause of morbidity in postoperative patients. Despite advances in surgical asepsis and improvements in sterile surgical techniques, SSIs continue to occur and are reported to happen in 3% to 12% of surgical wounds in veterinary patients.1–6 Surgical site infections not only necessitate increased hospitalization time and potential subsequent surgeries, but also cause frustration and increased costs to the client.

Antimicrobial-impregnated suture material has been purported to decrease bacterial colonization when tested in the laboratory setting.7–11 The antibacterial suture is coated with triclosan, a broad-spectrum antiseptic widely used in human personalcare products.12 Higher concentrations of triclosan work as a bactericide by multiple mechanisms and by attacking different structures in the bacterial cytoplasm and cell membrane.13 Triclosan-coated sutures have shown antibacterial efficacy against or decreased bacterial adherence to the suture for Escherichia coli, Staphylococcus aureus, methicillin-resistant S aureus, Staphylococcus epidermidis, methicillin-resistant S epidermidis, methicillin-resistant Staphylococcus pseudintermedius, and Klebsiella pneumoniae.7–10,14,15 Previous studies have been performed in the laboratory setting or in laboratory animals with direct bacterial inoculation of the surgical site.7,8,10,14

Despite the promising findings in laboratory animals, conflicting data exist in both human medicine and veterinary medicine when TC suture is used in a clinical situation. A retrospective veterinary study16 of 283 dogs undergoing tibial plateau leveling osteotomy found no difference when comparing SSI rates between TC and non-TC suture. Several meta-analyses of human studies pertaining to TC suture and SSIs have been performed. Some meta-analyses show that TC suture decreased the incidence of SSI,17–20 whereas others show that TC sutures did not decrease the incidence of SSI.21,22 Therefore, the ability of TC suture to decrease the incidence of SSI is still under debate.

We hypothesized that the incidence of SSI would be lower among dogs or cats undergoing surgical procedures performed with TC suture relative to non-TC suture (ie, tested the null hypothesis of no difference in incidence between suture types). The objective of the study reported here was to evaluate the prophylactic efficacy of TC suture used in surgical wounds of dogs and cats undergoing soft tissue, neurologic, and orthopedic surgical procedures. The incidences of SSI of surgical wounds closed with TC suture and surgical wounds closed with non-TC suture that occurred between the time of surgery and 1 month postoperatively were compared.

Materials and Methods

Dogs and cats undergoing any surgical procedure in an operating room were prospectively enrolled after client consent was obtained. The study protocol was approved by the Texas A&M University Institutional Care and Use Committee (protocol No. 2015–0113CA). Animals were not eligible for enrollment if no suture material was to be used (eg, feline castration), if the animal had a prior surgery at the same surgical site within 30 days, or if only tube placement or an interventional radiologic procedure was to be performed. Animals were excluded if a 30-day follow-up was not obtained. Each animal was permitted to enroll in the study only once.

A balanced, randomized assignment was made to non-TC or TC suture groups by computer randomization. When TC suture was assigned, all suture available as TC material (ie, TC polydioxanone,a TC poliglecaprone 25,b and TC polyglactin 910c) was used rather than non-TC suture. When non-TC suture was assigned, the same brand of suture was used but was non-TC material (ie, polydioxanone,d poliglecaprone 25,e and polyglactin 910f). Any additional suture not available as TC material that was requested by the surgeon was allowed (eg, nylon, polypropylene, and silk), mainly as procedural suture. Procedural sutures were defined as suture used to complete the procedure itself, such as suture to close an enterotomy or cystotomy incision or suture used for ligatures. Deep and subcutaneous layers of the surgical wound closures were performed with the previously mentioned suture (ie, polydioxanone, poliglecaprone 25, or polyglactin 910 in TC or non-TC forms). Skin sutures or staples not available as TC products were allowed. Standard techniques were used for surgical preparation and for surgical team preparation.

A surgical form was completed as the patient progressed through anesthetic induction, surgical preparation, surgery, and anesthetic recovery (Supplementary Appendix SI, available at: avmajournals.avma.org/doi/suppl/10.2460/javma.257.1.62). Factors were recorded on the surgical form as follows: ASA status, surgeons present, number of people who scrubbed for surgery, maximum number of people in the operating room at any time,2 anesthetic induction agent,23 duration of surgery,2,3 duration of anesthesia,3 and antimicrobial prophylaxis.1,24 Many of these factors have been associated previously with increased incidence of SSI.1–3 The surgical service was recorded as orthopedic, soft tissue, neurologic, or general surgery. At our institution, the general surgery service is a student-run surgical service through which mainly ovariohysterectomy, orchiectomy, and gastropexy are performed. Following the surgical procedure, a member of the surgical team completed the surgical portion of the form. Additional data collected included the following: wound category (ie, clean, clean-contaminated, contaminated, or dirty; Appendix),25 breach in sterile technique, hypotension (mean arterial pressure < 60 mm Hg), emergency procedure (yes or no), length of incision (in centimeters), person who performed most of the surgical procedure (ie, faculty, resident, intern, or student), procedural suture selected, and deep, subcutaneous, and skin closure suture materials and patterns. Whether a surgical implant was placed was also recorded (yes or no). Any type of nonabsorbable implant was considered a surgical implant such as bone plates, pins, wire, suture anchors, polypropylene mesh, or ameroid constrictor. Any omissions on the form were completed by review of the medical record, whenever possible.

An active 30-day surveillance for SSIs was performed. A published owner questionnaire5 was administered to each owner approximately 30 days postoperatively. This survey was used to classify wounds for the presence of an SSI according to the CDC definition.26 Briefly, the CDC defines an SSI on the basis of one of the following: purulent drainage from incision; microorganism isolated by microbiological culture; pain, swelling, redness, or heat requiring the incision to be opened; spontaneous dehiscence and microorganisms isolated by microbiological culture; or abscess formation at the surgical site. The CDC definition delineates between superficial, deep, and organ or body space infections; for the present study, infection present in any of these 3 categories was considered an SSI. This definition of SSI was similar to definitions of SSI used in other veterinary and human medicine studies.1,3,5,24,27 If the animal was presented to our institution for a recheck, information from direct examination of the wound was also used to determine whether an SSI had occurred. Any animal undergoing wound microbiological culture postoperatively was recorded, and microbiological culture results were collected.

The presence or absence (yes or no) of any incisional problem other than SSI was recorded. This included excessive redness, swelling, and seroma formation.

Statistical analysis

Prior to commencement of the study, exact binomial methods and calculation with statistical softwareg were used to determine the sample size that provided 95% confidence to detect an expected cumulative incidence of SSI in the non-TC suture group of 5.0%1 and an expected incidence of SSI in the TC suture group of 2.5%.8,28 The estimated sample size was 352 animals, which was corrected for attrition of 30% by dividing by 0.7 (70%) to yield an estimate of 503 animals/treatment group.

Data were analyzed by use of descriptive and inferential statistics. Categorical data were summarized by cross-tabulation of the outcome of interest (eg, SSI) and each independent categorical variable. Continuous variables were summarized as medians and ranges. For inferential statistical analysis, the bivariate association between the principal outcome variable (ie, SSI) and independent variables was quantified by use of ORs, and their 95% CIs were derived by use of maximum likelihood methods. Variables associated with SSIs at a significance level of P < 0.10 were included in multivariable modeling and included a stepwise forward procedure, with values of P < 0.05 to be retained in the model for any level of a polychotomous variable. All tri- and bivariable interaction terms were examined for those variables selected for the final multivariable model. Model fit was assessed by visual inspection of diagnostic plots of residuals. Additional analysis of categorical data with κ2 testing was performed. Analyses were performed with a commercially available software program,g and significance for all analyses was set at P < 0.05.

Results

Animals

One thousand ninety-three dogs and cats were recruited to the study between August 2015 and August 2017. Two hundred thirty-one animals were excluded for lack of follow-up, leaving 862 animals (794 dogs and 68 cats) in the study. Of these, 434 were assigned to the TC suture group and 428 were assigned to the non-TC suture group, slightly exceeding the stated goal of 352 animals with follow-up/group. The groups appeared similar at baseline for the considered variables of sex, neutered status, surgery type, and cleanliness of surgery site (Table 1).

Table 1—

Results of analyses for associations between patient variables and suture type (ie, TC suture or non-TC suture) used in 862 dogs (794) and cats (68) that underwent surgery.

Variable (No.)*No. with TC sutures (%)No. with non-TC sutures (%)P value†
Species (862)  0.410
  Canine396/794 (50)398/794 (50) 
  Feline38/68 (56)30/68 (44) 
Sex (862)  0.466
  Castrated male131/271 (48)140/271 (52) 
  Sexually intact female70/124 (56)54/124 (44) 
  Sexually intact male51/110 (46)59/110 (54) 
  Spayed female182/357 (51)175/357 (49) 
Surgical service (862)
  General155/310 (50)155/310 (50)0.585
  Neurologic9/16 (56)7/16 (44) 
  Orthopedic118/251 (47)133/251 (53) 
  Soft tissue152/285 (53)133/285 (47) 
Category (857)  0.254
  Clean343/702 (49)359/702 (51) 
  Clean-contaminated44/83 (53)39/83 (47) 
  Contaminated35/55 (64)20/55 (36) 
  Dirty9/17 (53)8/17 (47) 
Combined categories (857)  0.073
  Clean, clean-contaminated387/785 (49)398/785 (51) 
  Contaminated, dirty44/72 (61)28/72 (39) 

For some variables, data are missing such that the total number of animals is not 862.

Values of P < 0.05 are considered significant.

Procedural sutures used in the 862 animals were as follows: polydioxanone with polypropylene (n = 7), polydioxanone with poliglecaprone 25 (5), fluorocarbon (7), braided polyethylene (2), poliglecaprone 25 (37), none (380), polydioxanone (402), polyglactin 910 (1), polypropylene (11), and silk (10). Deep tissue closure sutures used were as follows: polydioxanone (n = 712), poliglecaprone 25 (57), and none (93). Subcutaneous tissue closure sutures used included the following: polydioxanone (n = 70), poliglecaprone 25 (698), and none (94). Skin closure sutures used were as follows: polydioxanone (n = 11), poliglecaprone 25 (773), polypropylene (2), none (13), staples (16), nylon (31), and a combination of poliglecaprone 25 with staples, nylon, or polydioxanone (16).

Bivariate analysis results

Of the 862 animals, 50 (5.8%) developed an SSI. Incidence of SSI was 6% (24/428) in the non-TC suture group and 6% (26/434) in the TC suture group. No significant (P = 0.809) difference was found in the incidence of SSI between groups. Variables significantly associated with SSIs by use of bivariate logistic regression were determined (Table 2).

Table 2—

Significant associations of SSIs with independent variables in 794 dogs and 68 cats that underwent surgery with the use of TC suture or non-TC suture.

 SSIs 
Variable (No.)*No. (%)OR (95% CI)P value
Sex (862)
  Castrated male20/271 (7)1 (reference)NA
  Sexually intact female2/124 (2)0.21 (0.05–0.88)0.033
  Sexually intact male6/110 (6)0.72 (0.28–1.85)0.501
  Spayed female22/335 (6)0.82 (0.44–1.54)0.546
Surgery service (846)
  General7/310 (2)1 (reference)NA
  Orthopedic20/251 (8)3.75 (1.56–8.98)0.003
  Soft tissue23/285 (8)3.80 (1.61–8.97)0.002
No. of people scrubbed in (842)§
  ≤ 320/475 (4)1 (reference)NA
  > 328/367 (8)1.88 (1.04–3.37)0.035
Duration of anesthesia (845)
  < 240 min19/516 (4)1 (reference)NA
  ≥ 240 min31/329 (9)2.72 (1.51–4.90)> 0.001
Duration of surgery (858)
  < 120 min20/536 (4)1 (reference)NA
  ≥ 120 min30/322 (9)2.65 (1.48–4.75)0.001
Primary surgeon (845)
  Faculty member16/251 (6)1 (reference)NA
  Intern or resident27/291 (9)1.50 (0.79–2.86)0.215
  Student7/303 (2)0.35 (0.14–0.86)0.022
Break in sterile technique (839)
  No break33/661 (5)1 (reference)NA
  Break16/168 (10)2.00 (1.08–3.73)0.029
Implant used (862)
  No31/638 (5)1 (reference)NA
  Yes19/224 (9)1.81 (1.01–3.28)0.048
Incision length (846)#
  ≤ 10 cm17/501 (3)1 (reference)NA
  > 10 cm32/345 (9)2.91 (1.59–5.33)< 0.001
ASA status (862)
  110/335 (3)1 (reference)NA
  > 140/527 (8)2.67 (1.32–5.41)0.007

Sixteen cases from the neurologic surgery service excluded from total

Number of people scrubbed in for surgery (median, 1; range, 1 to 12)

Duration of anesthesia (median, 213 minutes; range, 48 to 500 minutes).

Duration of surgery (median, 103 minutes; range, 10 to 314 minutes).

Incision length (median, 9 cm; range, 0.3 to 70 cm).

NA = Not applicable.

See Table 1 for remainder of key.

The proportion of animals with any incisional problem (other than SSI) among those in the non-TC suture group (10.3% [44/428]) was similar (P = 0.880) to that of animals in the TC suture group (10.8% [47/434]).

Animals undergoing surgery in the general surgery service were evaluated for SSIs separately. Of 155 animals in the TC suture group, 2 (1.3%) had SSIs; of 155 animals in the non-TC suture group, 5 (3.2%) had SSIs. For animals undergoing surgery in the general surgery service, the incidence of SSI did not differ significantly (P = 0.444) between groups. Clean surgeries were evaluated for SSIs separately. Among the clean surgeries, SSIs were detected in 19 of 343 (5.5%) animals in the TC suture group and 18 of 359 (5.0%) animals in the non-TC suture group; these proportions did not differ significantly (P = 0.887) between groups.

Multivariable analysis results

To assess the effects of variables associated at a level of P < 0.10 with SSI adjusted for the effects of other associated variables, forward stepwise logistic regression was performed. The final multivariable model (Table 3) included the following variables: incision length > 10 cm, soft tissue surgery service, and anesthesia duration > 240 minutes. Neither the trivariate nor any of the bivariate interaction terms included in the final model were significant. Changes in magnitudes of the estimated ORs in the multivariable model from their bivariate values indicated some degree of confounding among these variables. Including suture type (ie, TC or non-TC material) with variables in the final model did not alter the magnitude or significance of the associations observed in Table 3 (data not shown), and suture type (ie, the use of non-TC suture relative to TC suture) was not significantly (P = 0.648) associated with SSI (OR, 0.87; 95% CI, 0.48 to 1.57).

Table 3—

Final multivariable model and ORs for variables significantly associated with odds of developing an SSI in 794 dogs and 68 cats that underwent surgery with the use of TC suture or non-TC suture material.

VariableOR (95% CI)P value
Incision > 10 cm long1.95 (1.03–3.70)0.041
Orthopedic surgery service1.86 (0.70–4.97)0.216
Soft tissue surgery service2.47 (1.02–6.01)0.046
Anesthesia duration > 240 min2.16 (1.05–4.45)0.037

See Table 1 for key.

Microbiological culture results

Thirty-five specimens from 35 patients were submitted for microbiological culture; 34 patients had positive microbiological culture results, ranging from 1 to 6 bacteria isolated. Of the 34 specimens that yielded positive microbiological culture results, 17 (50%) were polymicrobial and 17 (50%) were monomicrobial. No significant (P = 0.731) difference was found in the proportion of polymicrobial infections for animals in the TC suture group (8/18) and animals in the non-TC suture group (9/16). Also, no significant (P = 0.468) difference was found in the number of bacteria isolated from animals in the TC suture group (median, 1; range, 0 to 4; n = 19) and animals in the non-TC suture group (median, 2; range, 1 to 6; 16). The most commonly isolated species from animals with SSI were as follows: S pseudintermedius (n = 15), Streptococcus spp (8), Enterococcus spp (8), and Pseudomonas spp (6). Although S pseudintermedius was isolated less often from animals in the TC suture group (5/19) than from animals in the non-TC suture group (10/16), this difference was not significant (P = 0.061). Methicillin-resistant S pseudintermedius was isolated from 9 animals. The proportion of animals from which methicillin-resistant S pseudintermedius was isolated among the TC group (3/19) did not differ significantly (P = 0.447) from that in the non-TC suture group (6/16).

Discussion

In the present study, no significant difference was detected in the incidence of SSI between animals in which TC suture was used and those in which non-TC suture was used to close surgical wounds. Additionally, no significant difference was detected in incisional problems between animals in which TC suture was used and those in which non-TC suture was used. Interest in TC sutures has increased in human medicine over the last decade, with several randomized, controlled trials assessing the effectiveness of TC suture.29–32 Studies of human patients assessing the ability of TC suture to decrease the incidence of SSI have yielded conflicting results. No decrease in SSI was found when TC suture was used in patients undergoing abdominal wall closure following gastrointestinal surgery,29 midline laparotomy,30 or total hip and total knee arthroplasty.31 However, TC sutures decreased SSIs in other studies that involved pediatric surgery,32 adults undergoing abdominal wall closure,33 and a variety of surgical procedures.28 Additionally, meta-analyses on the subject have reported contradictory results, with some reporting a decreased incidence of SSI when TC sutures are used19,20 and some reporting no difference in SSIs between TC and non-TC sutures.21,22

One explanation of the different findings between the present study and some human studies may pertain to suture selection and the type of sutures studied in human patients. Many of the human trials include polyglactin 910 and polydioxanone for fascial closure. In a meta-analysis in which polydioxanone sutures were evaluated separately, no effect of antimicrobial coating with triclosan was found on the rate of SSI.34 However, when polyglactin 910 has been compared with TC polyglactin 910, a decrease in SSIs in the TC suture group has been detected.28,34 Polyglactin 910 is a braided suture with greater surface area, thus increasing the risk of bacterial adherence in comparison with monofilament suture material.15,34 It has been theorized that the increased surface area of the multifilament may also lead to a higher triclosan concentration.34 In the present study, polyglactin 910 was available as an option for surgeons to use, but was selected for only 1 of the 862 animals, precluding our ability to comment on SSIs and the use of polyglactin 910. Sutures used in the present study were mainly monofilament sutures, and triclosan coating may not be beneficial in preventing SSI in the use of monofilament sutures.34

Findings of meta-analyses in human studies17,19,20,29 have suggested that TC suture may decrease SSI risk and that this effect is particularly obvious in clean wounds. In clean wounds, very few bacteria are present and the triclosan may be able to eliminate the bacteria. In more highly contaminated wounds, the number of bacteria may overwhelm the ability of the TC suture to prevent an SSI. In the present study, we evaluated the 702 clean surgeries independently and still did not find a significant difference in the incidence of SSI between TC suture and non-TC suture groups. It is possible that the benefits of TC suture in clean surgeries in human patients are not realized in veterinary patients.

Methicillin-resistant S pseudintermedius has been shown to adhere to different suture materials used in veterinary medicine.15 Coating suture with triclosan results in significantly less adherence of methicillin-resistant S pseudintermedius to the suture.15 In the present study, S pseudintermedius was isolated less frequently from animals with SSI undergoing microbiological culture in the TC suture group (5/19 [26%]) than from animals with SSI undergoing microbiological culture in the non-TC suture group (10/16 [63%]), although this difference was not significant (P = 0.061). It is possible that the decreased frequency in isolation of S pseudintermedius in the TC suture group was the result of decreased adherence of S pseudintermedius to the suture.15

Animals with incisions > 10 cm in length in the present study were more likely to have an SSI. It could be hypothesized that a smaller incision results in less tissue exposure during surgery and less opportunity for bacterial colonization of wound margins. To the authors' knowledge, other than studies comparing minimally invasive techniques to open techniques, only 1 previous study35 has related incision length to incidence of SSI in either veterinary surgery or human surgery. That study included horses undergoing colic surgery and showed that horses with longer incisions (over 27 cm) were more likely to have an SSI.35 A study6 comparing veterinary SSI rates in wounds after minimally invasive versus open surgery concluded that minimally invasive surgery may be associated with a lower rate of SSI. Although the study compared open versus minimally invasive approaches, it did not directly compare lengths of surgical incisions, although shorter incisions may be assumed in the minimally invasive group.

Anesthesia duration of > 240 minutes was found to be a risk for SSI. This was likely the result of several factors. Longer procedures require longer anesthesia. Duration of anesthesia has been shown to increase the incidence of SSI in human surgeries.36 Although surgical duration was not a significant risk factor for SSI in the multivariable analysis, this was attributable to its association with duration of anesthesia; accounting for one factor included the effects of the other. Longer surgical procedures expose the tissues to room air for a longer duration and may lead to increased tissue trauma, tissue desiccation, and possibly increased exposure to bacteria. Nevertheless, prolonged anesthesia without prolonged surgical times may also be caused when feeding tubes, invasive monitoring, or other instrumentation is placed before or after surgery. The necessity of implementing any of these techniques may indicate more debilitated patients. A patient factor score was not used in the present study but could be evaluated in future studies and may correspond with the ASA status, which was also predictive of SSI in the present study.

Undergoing surgery with the soft tissue surgery service was associated with increased incidence of SSI, which could be expected for a variety of reasons. The soft tissue surgery service at our institution tends to operate on the most critical patients, with the orthopedics and general surgery services operating on a more elective basis. As mentioned above, the soft tissue surgery service could potentially be a confounding variable with incision length as well as anesthesia duration. Further, the soft tissue surgery service was more likely to be performing most of the dirty surgeries, which have a higher incidence of infection. A previous study5 reported that surgical category (ie, clean, clean-contaminated, contaminated, and dirty) was a risk factor for developing SSIs. In the present study, we grouped the procedures and compared so-called clean surgery, including only clean surgeries, with so-called not-clean surgery, including clean-contaminated, contaminated, and dirty surgeries. No significant difference was found between clean and not-clean surgeries. We suspect that the lack of a significant difference was the result of a type II error, and if more cases had been included, a significant difference in SSI could have been detected at least between the extremes of the surgical wound classification (ie, clean vs dirty). Unfortunately, only 17 dirty procedures were included in the present study, precluding further analysis.

In the univariate analysis, sexually intact females had a protective effect for development of an SSI because sexually intact females had fewer infections than spayed females, sexually intact males, and neutered males. This finding is also reported in humans. Following surgery, human males have been shown to be at increased risk for SSIs.37,38 One explanation may be accelerated cutaneous wound healing as a result of estrogen in females. In a research setting, estrogen treatment accelerates cutaneous wound healing39 and topical estrogen preparations have been used in elderly patients to promote quicker and more effective wound healing.40 Sex difference in wound healing in dogs has been proposed, with female dogs proposed to heal more quickly than male dogs.41 The finding that being a sexually intact female had a protective effect for development of SSIs could also be a confounding variable associated with general surgery and student surgeons, both of which were also factors protective of SSIs. It is also possible that this association was spurious, resulting from chance alone. Without replication of this finding, preferably in studies designed to test this specific hypothesis, this finding should be interpreted with caution.

The present study had a number of limitations. It would have been preferable to have 1 observer diagnose SSIs for consistency. In the present study, this was not possible because patients were dispersed throughout a large geographic area. Many were not able to conveniently have follow-up at our institution because of the travel associated, and we would have eliminated a large pool of our clients if a return to our institution were mandatory. To minimize the problem of multiple observers, we used specific criteria to diagnosis SSIs and a previously published survey.

Variability resulting from surgeon preferences was not controlled for in the present study. Surgeons often have a certain way of performing different procedures, and asking them to change their protocol would lead to noncompliance. For example, suture material selections and suture patterns were not standardized. Recording of the suture materials was performed immediately following surgery. Although the recording was timely, it is possible that misrecording occurred. Another limitation was the use of prophylactic antimicrobials by some surgeons in some procedures. Exclusion of animals receiving prophylactic antimicrobials or currently receiving antimicrobials would have eliminated nearly all orthopedic patients and many of the critically ill patients. Another limitation was the amount of suture material used. The amount of suture placed in a patient is minimized by the surgeon but varies depending on the procedure, surgeon preference, and individual animal. We assumed that random assignment and comparability of groups at baseline accounted for any differential effects resulting from surgeon preferences.

Selection bias could have occurred in the present study. All animals that had undergone surgery within 30 days at the same surgical site were excluded. This may have excluded many animals that already had an SSI, therefore lowering the number of dirty surgeries. A major potential bias was the desire for surgeons to have a low SSI rate. This desire may preclude a surgeon from reporting an SSI. This potential bias was mitigated by use of a client questionnaire and a published definition of SSI.

ABBREVIATIONS

ASA

American Society of Anesthesiologists

SSI

Surgical site infection

TC

Triclosan-coated

Acknowledgments

Funded by the ACVS Foundation Novartis Animal Health US Incorporated Antimicrobial Sutures Grant Program. Funding sources did not have any involvement in the study design, data analysis and interpretation, or writing and publication of the manuscript.

Presented in abstract form at the American College of Veterinary Surgeons Symposium, Phoenix, Ariz, October 2018.

Footnotes

a.

PDS Plus Antibacterial, Ethicon Inc, Somerville, NJ.

b.

Monocryl Plus Antibacterial, Ethicon Inc, Somerville, NJ.

c.

Vicryl Plus Antibacterial, Ethicon Inc, Somerville, NJ.

d.

PDS II, Ethicon Inc, Somerville, NJ

e.

Monocryl, Ethicon Inc, Somerville, NJ.

f.

Vicryl, Ethicon Inc, Somerville, NJ.

g.

S-PLUS, version 8.2, TIBCO Inc, Seattle, Wash.

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Appendix

Definitions of wound category.25

Clean wounds: An operative wound in which the respiratory, alimentary, and genitourinary tracts and the oropharyngeal cavity are not entered. Clean wounds are created in aseptic conditions.

Clean-contaminated wounds: An operative wound in which the respiratory, alimentary, or genitourinary tract is entered under controlled conditions and without unusual contamination. Contamination of a clean wound due to a break in sterile technique may be in this category.

Contaminated wounds: Open, fresh, traumatic wounds. An operative wound in which a major break in sterile technique occurred or gross spillage from the gastrointestinal tract. Incisions into a site with acute, nonpurulent inflammation.

Dirty wounds: Old traumatic wounds with devitalized tissue or wounds with clinical infection or perforated viscera. Pus or acute bacterial infection with purulent exudates encountered during surgery would be in this category.

Supplementary Materials

Contributor Notes

Address correspondence to Dr. Thieman Mankin (kthieman@cvm.tamu.edu).