Table 3.1 Swabbing techniques.
| Swabbing technique | Collection method |
|---|---|
| Levine technique | The swab is rotated over 1 cm2 for 5 sec with sufficient pressure to exude fluid from the tissues |
| Z‐technique | The swab is rotated as it is moved from margin to margin, without touching the skin edges, in a 10‐point fashion |
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).
Figure 3.1 For the Levine technique, the swab is contacting the wound bed only, with sufficient application of pressure to result in exudation of fluid from the underlying tissues.
Source: Adapted from Weese JS. Wound sampling for culture and cytology. Clinician's Brief, March 2020. www.cliniciansbrief.com/article/wound‐sampling‐culture‐cytology.
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.
Figure 3.2 (a) A craniocaudal (CC) view of a TPLO with periosteal reaction evident at the distal aspect of the implant. (b) A lateral view of a TPLO with periosteal reaction evident at the cranial aspect of the implant, as evidenced by the increased bone density in this region corresponding to the location of periosteal reaction on the CC view. (c) A CC view following implant removal, highlighting the previously identified periosteal reaction. (d) A lateral view following implant removal, highlighting the periosteal reaction outlining the previous implant.
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].
Figure 3.3 A dehisced lateral stifle incision with local erythema and purulent material present at the skin edges and present on the underlying muscle belly. This is considered to be a deep SSI.
Table 3.2 Surgical site infection (SSI) definitions.
| Surgical site infection category | Criteria |
|---|---|
| Superficial SSI |
MUST:Occur within 30 days of surgeryInvolve only the skin or subcutaneous tissues of the incisionMust have AT LEAST one of the following:Purulent discharge
|