Preventing Surgical Site Infections: Are we swabbing/treating the wrong orifice? by Steven P. LaRosa, M.D.

A few Friday afternoon consults for prosthetic joint infections got me thinking about the whole issue of preventing surgical site infections (SSI). It is quite common in cardiothoracic surgery and orthopaedic surgery for patients to be screened pre-operatively for Staphylococcus aureus colonization with a nasal culture or PCR. Those who are positive are prescribed nasal Mupirocin to rid the carrier state in hopes of decrease the risk of SSI. Additionally, since patients can carry S. aureus elsewhere (axilla, inguinal, perirectal) patients are instructed to bathe with Chlorhexidene pre-operatively. Despite these decolonization attempts one study showed that 20% of patients remained colonized with MRSA and continued to have SSIs (Baraz et al. Clin Orthop Related Res 2015).

What occurred to me in a review of the literature is that maybe we are focusing on the wrong site of colonization. Approximately 20% of people have intestinal colonization of the gastrointestinal tract. This can be measured by culture of the stool, or swab cultures taken from the inguinal, perineal or perirectal areas. While nasal and intestinal colonization often go together, 10% of all colonized patients will only be colonized intestinally, and one in three patients colonized intestinally have negative nasal cultures. This raises the issue that we are missing a lot of colonized patients by just assessing the nares. Furthermore, given the proximity of the anus to a potential prosthetic hip or knee joint it raises the critical importance of cleaning the perineal and peri-rectal areas preoperatively. I would suggest that this is so important that we probably should not leave this to the patients but should have thorough wiping of these areas in the preoperative area with Chlorhexidene wipes (“nose to toes disinfection”).

A new hypothesis on the development of surgical site infections also indicates that we should be paying more attention to intestinal colonization with Staphylococcus aureus. In a study by Krezalek and colleagues (Ann Surg. 2017 Feb 9) mice who had their guts colonized with MRSA prior to a partial hepatectomy, and trauma to the rectus muscle developed infections at the rectus muscle surgical site. Mice that had their surgical wounds painted with MRSA or had MRSA administered intravenously did not develop infections at the rectus muscle surgical site. Circulating neutrophils from mice captured by flow cytometry demonstrated MRSA in their cytoplasm. This raises the possibility that gut derived MRSA are carried via neutrophils (Trojan horse) serve as a mechanism of surgical site.

The gut hypothesis of surgical site infection is testable. Patients could be screened pre-operatively for intestinal colonization with Staph aureus via a peri-rectal swab. As systemic antibiotics have little effect on decreasing intestinal colonization, patients found to be positive for S. aureus could be randomized to oral Vancomycin or placebo in addition to standard of care. A previous study has demonstrated that Vancomycin given orally at a dose of 250mg every 6 hours for 5 days is effective at eradicating gut colonization. Repeat per-rectal swabs could be obtained at the time of surgery and PJI event rates could be calculated.