3.1 Introduction

Prompt and accurate diagnosis of surgical site infections (SSIs) is important for patient management and facility infection control. Identifying infections promptly allows for early intervention. Differentiation of SSI from inflammation helps avoid unnecessary treatment. A good understanding of infection rates and early identification of increases in infection rates can allow for an earlier investigation and intervention. Therefore, SSI surveillance is a critical area for any surgeon, surgical team, and facility.

3.2 Identification of Surgical Site Infections

A superficial incisional SSI is confined to the skin and subcutaneous tissues of the incision and must be differentiated from cellulitis. The Centers for Disease Control and Prevention (CDC) defines cellulitis as localized redness, heat, and swelling, without purulent discharge or identification of microorganisms [1]. The clinical features associated with cellulitis are often identified in postoperative wounds and presumed to indicate SSI without performing diagnostic testing to identify a causative organism, thus confirming an active SSI [2, 3]. Subsequently, when reviewing the literature, a category such as “infection‐inflammation” may be reported, making it difficult to accurately detect and report SSI rates based on CDC definitions [2, 3]. One such study including the infection‐inflammation category defines infection‐inflammation as the presence of purulent discharge, a localized abscess or fistulous tract associated with the incision or the presence of three or more of the following: redness, swelling, heat, pain, serous discharge, and dehiscence [3]. While some of the cases collected in this category may appropriately represent an SSI, it does not distinguish SSI from cellulitis and as such may be falsely increasing the reported SSI rates. Other studies have reported SSI rates based on CDC definitions including positive culture results, while also reporting an infection‐inflammation rate to encompass those patients presenting with abnormal incisions [4].

Early detection and intervention for SSIs is critical. Löfqvist et al. identified marked elevations of serum C‐reactive protein (CRP) and serum amylase A (SAA) 6 days following tibial plateau leveling osteotomy (TPLO) [5]. The cut‐off values reported (CRP >43.9 mg/L, SAA >63.8 mg/L) may be used for patients both with and without clinical evidence of an active SSI and may therefore lead to earlier detection of subclinical SSIs [5]. While these serum markers may be able to identify subclinical SSIs, the clinical utility of this test is low as there are no clinical criteria that can be monitored to determine which patients to test. Following discharge from the hospital, owners should be advised to monitor the surgical site for evidence of localized swelling, pain, heat, or erythema. If any of these signs are detected, evaluation by a veterinarian should be sought.

Clinically, identification of SSIs will require gross reassessment of the surgical site to differentiate between cellulitis and infection as defined above and allow for collection of aseptic samples to identify microorganisms via cytology or bacterial culture. This may include direct swabbing of the wound or deep fine needle local aspirates. Before collecting a direct swab, the wound should be lavaged with sterile saline and any devitalized tissues debrided. The swab should be collected from the healthiest appearing portion of the wound bed. Two direct swabbing techniques have been described and are recommended to improve the chances of collecting a representative sample (Table 3.1). Of the two, the Levine technique (Figure 3.1) is considered superior [6]. When collecting a deep local fine needle aspirate, known regions of contamination should be avoided and the skin should be cleaned with alcohol to reduce the risk of skin contaminants. If microorganisms are identified cytologically from your sample, a bacterial culture and susceptibility test is recommended to further guide therapy. Radiographic assessment for evidence of lucency surrounding implants or evidence of osteomyelitis should also be considered to determine the extent of the suspected SSI. Radiographic evidence to support a deep SSI causing osteomyelitis may include periosteal reaction and bone lysis surrounding the implants (Figure 3.2).

As not all owners will seek veterinary care for perceived minor changes at the surgical site, another tool in our arsenal to improve detection of SSI is utilization of surveillance programs. Lack of communication between the surgical facility and primary care veterinarian can also result in underidentification of SSI rates, particularly when owners may return to their primary care veterinarian for minor complications as these may not be reported to the surgeon. Further, deficiencies in medical record quality can impact retrospective identification of SSIs.

Two recent prospective veterinary studies on postdischarge surveillance programs reported that 28–35% of identified SSIs were not documented in the medical record, leading to falsely lower SSI rates when retrospectively evaluated using medical records alone [4, 7]. Both studies carried out owner questionnaires at 30 days postoperatively and one study repeated the questionnaire at 90 days for patients having a surgical implant [4, 7]. This active surveillance approach will yield more accurate SSI information; however, these types of active surveillance approaches require time, effort, and corresponding personnel costs.

Developing an active surveillance protocol is an important quality control tool, but it can be challenging to achieve due to the time commitment involved [4]. However, empowering a member of the surgical team to champion an active surveillance program is highly recommended to ensure uptake and quality control. Alternatively, improving passive surveillance methods, beyond routine examination at the time of suture removal, may also be beneficial. Emphasizing the importance of SSI reporting from referring veterinarians and clients, along with defined measures of surgical site assessment to report, may help to improve the accuracy of SSI rates within your hospital [4].

More recently, electronic approaches to surveillance have been investigated. The proliferation of smartphones and email access creates the potential for easy, cost‐effective monitoring and data collection. In the future, it is likely that approaches using personal devices will become common SSI surveillance tools.

For SSIs to be appropriately identified, the use of specific criteria to define SSIs must be employed. The CDC has categorized SSIs as superficial incisional SSI, deep incisional SSI (Figure 3.3), and organ/space SSI based on specific criteria (Table 3.2). Recently, these categories have been redefined with regard to implant‐associated SSI, such that an implant‐associated SSI must occur within 90 days of surgery [1].