All Surgical Site Infections Are Not Equal To the Editor


he recent editorial1 highlighting the article by Belani et  al.2 promoted an important misconception that all surgical site infections (SSI) are created equal. Assuming that all SSIs are the same leads to the erroneous conclusion that the often-referenced study by Kurz et  al.,3 that showed that soft tissue SSIs during colon surgery are decreased by forced-air warming, also applies to infections involving implanted foreign materials such as periprosthetic joint infections (PJI) after total joint replacement surgery. The implantation of foreign material in the body fundamentally changes the pathophysiology of the infectious process. An inoculum of >1 million bacteria is required to cause a soft tissue SSI, and the bacteria usually enter the wound from the adjacent skin or cut bowel.4 The infection usually manifests within days and is easily treatable. In sharp contrast, it has been shown that a single bacterium can cause a PJI, and it usually enters the wound as airborne contamination.5–7 The infection may take up to a year to manifest and is generally catastrophic. The primary difference between the two is the ability of bacteria to form a biofilm protective coating in the presence of implanted foreign materials but not in soft tissue. Therefore, the results of the Kurz study3 cannot be applied to PJIs. Conflicts of Interest: Scott Augustine, MD, is the CEO and an investor in ATM, manufacturer of HotDog® patient warming. Scott Augustine, MD Augustine Temperature Management LLC Eden Prairie, Minnesota [email protected] REFERENCES 1. Weissman C, Murray WB. It’s not just another room. Anesth Analg 2013;117:287–9 2. Belani KG, Albrecht M, McGovern PD, Reed M, Nachtsheim C. Patient warming excess heat: the effects on orthopedic operating room ventilation performance. Anesth Analg 2013;117:406–11 3. Kurz A, Sessler DI, Lenhardt R. Perioperative normothermia to reduce the incidence of surgical-wound infection and shorten hospitalization. Study of Wound Infection and Temperature Group. N Engl J Med 1996;334:1209–15 4. Elek SD, Conen PE. The virulence of Staphylococcus pyogenes for man; a study of the problems of wound infection. Br J Exp Pathol 1957;38:573–86 5. Lidwell OM, Lowbury EJ, Whyte W, Blowers R, Stanley SJ, Lowe D. Bacteria isolated from deep joint sepsis after operation for total hip or knee replacement and the sources of the infections with Staphylococcus aureus. J Hosp Infect 1983;4:19–29 6. Whyte W, Hodgson R, Tinkler J. The importance of airborne bacterial contamination of wounds. J Hosp Infect 1982;3:123–35 7. Petty W, Spanier S, Shuster JJ, Silverthorne C. The influence of skeletal implants on incidence of infection. Experiments in a canine model. J Bone Joint Surg Am 1985;67:1236–44 DOI: 10.1213/ANE.0000000000000104

April 2014 • Volume 118 • Number 4

In Response The subject of intraoperative hypothermia and its prevention is a complex issue. As pointed out in our editorial,1 on the one hand, there are studies demonstrating a reduced incidence of surgical wound infections when normothermia is maintained, while on the other hand, articles by Belani et al.2,3 demonstrate that the most common form of hypothermia prevention, forced-air warming, increases the number of particles above the surgical field. How this increase in particle numbers translates into infective potential is unclear because the bacterial burden of these particles has not been measured. It is the bacterial content of these particles that will determine their infective potential. As Augustine4 points out, the infective potential of a bacterial inoculum is dependent on the material inoculated. Living tissue requires a larger inoculum than prosthetic material to become infected. A joint prosthesis, such as a hip or knee replacement, is especially vulnerable to a small inoculum and thus the precautions taken to prevent contamination.5 However, even suture material, polyfilament more than monofilament, can be a nidus for infection6,7 as can mesh used for a hernia repair.8 In fact, under experimental conditions, bacterial adherence was seen with an inoculum of

All surgical site infections are not equal.

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