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Evidence is mounting that the vast majority of surgical site infections (SSIs) are caused by microorganisms on patients’ skin and in their nares, meaning intensifying and improving skin prep and nasal decolonization could greatly reduce SSIs.
“Almost all SSIs arise from the patient’s microbiome,” the author of a recent research review concludes.1 “The occurrence of SSIs can be viewed as a perioperative failure to control the microbiome.”
A leading voice in infection control for decades, Richard Wenzel, MD, MSc, is emeritus chairman of the Department of Internal Medicine at Virginia Commonwealth University Medical Center in Richmond.
“There is increased recognition of the importance of the microbiome in general — that it is a good thing in the right composition with the right numbers of our own organisms and normal flora,” he tells Hospital Infection Control & Prevention. “Most of the work has been done in the GI tract, and there hasn’t been as much focus on the microbiome of the skin or the nares.”
The Centers for Disease Control and Prevention (CDC) estimates that SSIs infect some 160,000 to 300,000 patients annually, with 2% to 5% of all operations resulting in infections.2 SSIs are estimated to add a week to hospital stays and some $3,000 to $29,000 in additional costs of care.3
If most of these infections can be traced to the incision-site skin and patient nares, a redoubling of current efforts to address these sources could have substantial impact. Narrowing in on the microbiome in recent years comes after some misguided attempts to address infections from non-significant sources, including the air in operating rooms, he notes. Studies in the 1980s — subsequently found to be flawed — led to widespread implementation of laminar flow hoods in ORs used for orthopedic procedures.
“The preponderance of data show that air really is unimportant,” Wenzel says. “When you look at the real data, which is what I tried to do here, almost all of the infections that we know about come from the patients’ own microbiome. It’s possible we will find evidence in the next 10 years — with rare exceptions — that the microbiome is the source of all SSIs.”
The key studies supporting this contention include those that have found using chlorhexidine skin preparation at the incision site — compared to using povidone iodine — reduced SSIs by 40% or more.4 Other studies show SSI reductions through use of nasal decolonization via mupirocin.5 More recently, two studies6,7 have gone beyond mupirocin to look at use of broad-spectrum topical nasal antiseptic administered once prior to the operation and then several times daily thereafter. These studies, which Wenzel warns must be confirmed by subsequent research, showed “remarkable” SSI reductions.
HIC asked Wenzel to comment on the important implications of the microbiome to SSI reduction in the following interview, which has been edited for length and clarity.
HIC: You found that eradicating bacteria from the skin and nasal sites prior to surgery dramatically reduces SSIs. Are the prevention practices cited currently widely implemented?
Wenzel: For the skin, chlorhexidine prep is standard now. I cite two studies that were instrumental, showing a 40% to 45% reduction in surgical site infections regardless of species. In addition, I would say the majority of places are currently using mupirocin for nasal decolonization. I cite two studies in orthopedics — one with back surgery and the other with joint implants — looking at a broad-spectrum [nasal] antiseptic. That is relatively new, but there are places beginning to use that instead of a drug like mupirocin, which targets gram-positive organisms. Maybe there is more to the nose than we thought, and a nasal antiseptic that would target both gram positives and gram negatives might be the way to go. That is sort of a little bit ahead of what we know so far. But the results so far in two studies showing a 70% [SSI] reduction in difficult operations is pretty remarkable. We have to see whether that will hold up. We need to know more about the nares as a source of gram negatives as well as other gram positives, including Staph aureus.
HIC: Regarding the studies on the non-mupirocin nasal antiseptic, it sounds like if that efficacy is borne out, it would be a game-changer for SSIs.
Wenzel: It would be major because mupirocin studies show roughly a 60% reduction in Staph aureus infections. What the nasal antiseptic studies so far suggest — and I want to be cautious — is more than a 70% reduction in total surgical site infections. That is huge. If that holds up, that means not only are the nares the source of gram positives, but probably gram negative [infections], which people haven’t really talked about before. There was one dose of the broad-spectrum nasal antiseptic prior to the incision and then [daily doses] for one to two weeks afterwards.
That raises the question whether postoperative carriage in the nose is an important source of SSIs. I don’t think we know yet, but these two studies make you wonder. Because most of the doses occurred after the surgery.
HIC: Are we starting to see reductions in SSIs overall due to these practices?
Wenzel: Certainly, for the chlorhexidine, no question. In terms of high-risk operations like orthopedic implants, mupirocin over the last decade has become routine. I don’t know the answer to that yet for the use of the nasal antiseptics in the last three to five years. The orthopedic literature shows if you use mupirocin, you clearly cut down on Staph aureus SSIs, both for implants and non-implants. If you look at the softer data in the national trends of surgical site infections after joint [implants], the CDC shows roughly a 40% reduction in infection rates over the last 15 years. Those trends are there, but that is just confirmatory data. I wouldn’t rely a lot on ecologic data, but it is consistent with what people are finding in individual studies.
HIC: In the paper, you describe a “map of the microbiome,” including research8 on Propionibacterium acnes that reside beneath the skin. Can you elaborate on this issue?
Wenzel: Darouiche et al.4 showed if you use chlorhexidine as a prep instead of an iodophor, you reduce all surgical site infections by 40%, but they didn’t culture everybody’s nose and skin ahead of time and show which organisms were reduced all the way. I looked for confirmatory microbiological data, where people have looked at a specific organism before, during, and after surgery. A number of those studies use marker organisms [like P. acnes]. It is primarily on the upper chest and upper back. You would think if the microbiome is important, surgeries in those areas would show [SSIs] disproportionately with that organism — and that is exactly what happened. So it is confirmatory data for the large overall infection rate reductions.
One of the second messages was that these organisms are in the dermis, below the epidermis, and so as a result, no current antiseptics are perfect. They do not reach the dermis. I tried to show that an acne drug was actually effective because it works to get into the dermis and actually get to the organism that is contributing to the acne. The number of the organisms are then reduced. In the future, I think there will be some studies to look at using a drug that gets into the dermis, and whether that will reduce not only Staph aureus but Staph epi, which lives in the dermis as well as the epidermis.
Financial Disclosure: Peer Reviewer Patrick Joseph, MD, reports that he is a consultant for Genomic Health, Siemens, and CareDx. Senior Writer Gary Evans, Editor Jesse Saffron, Editor Jill Drachenberg, Nurse Planner Patti Grant, RN, BSN, MS, CIC, and Editorial Group Manager Terrey L. Hatcher report no consultant, stockholder, speaker’s bureau, research, or other financial relationships with companies having ties to this field of study.