Surgical site infections (SSIs) are now the most common cause of hospital-acquired infections (HAIs), accounting for approximately 20% of all HAIs in hospitalized patients. Approximately 160,000–300,000 SSIs occur each year in the United States and 2%–5% occur in patients undergoing inpatient surgery. SSIs are associated with worse outcomes, including a 2- to 11-fold increase in the risk of mortality. Although most patients recover from an SSI without long-term adverse sequelae, 77% of mortality in patients with an SSI can be directly attributed to the infection itself. Attributable costs of SSI vary depending on the type of operative procedure and the type of infecting pathogen, but SSIs are believed to account for $3.5 to $10 billion annually in health-care expenditures. On average, SSIs extend hospital length of stay by 7–11 days and increase the cost of hospitalization by more than $20,000 per admission.
All surgical wounds are contaminated by bacteria, but only a minority result in clinical infections. In most patients, an infection does not develop because innate host defenses are quite efficient in eliminating contaminants at the surgical site. Development of SSI after surgery depends on complex interactions between (1) patient-related factors such as age, obesity, diabetes, host immunity, and nutritional status (2) procedure-related factors such as placement of a foreign body, duration of operation, skin antisepsis, and the magnitude of tissue trauma; (3) microbial factors that mediate tissue adherence and invasion or that enable the bacterium to survive the host immune response and to colonize or infect the host concurrently; and (4) perioperative antimicrobial prophylaxis.
Surgical Site Infection
Classification of SSI
Classification of wounds can be based on the degree of bacterial load or contamination that they contain. Since the landmark 1964 National Academy of Sciences’ National Research Council study on the use of ultraviolet lights in the operating room (OR), wounds have been classified by the level of risk of contamination. The four categories are clean, clean/contaminated, contaminated, and dirty/infected. This classification of the degree of contamination in the surgical site during surgery has become the traditional system for predicting infection risk in surgical wounds.
SSIs are classified into three groups: (1) superficial incisional, (2) deep incisional, and (3) organ/space. A superficial incisional SSI involves only the skin or subcutaneous tissue, a deep incisional SSI involves the fascia or muscular layers, and an organ/space SSI involves any part of the body opened or manipulated during the operative procedure, excluding the previously mentioned layers. The criteria used for defining an SSI are listed in Box 28.1 . The identification of SSI involves interpretation of clinical and laboratory data. The Centers for Disease Control and Prevention (CDC) has derived standardized surveillance definitions and these criteria must be applied consistently when classifying an SSI.
Superficial incisional SSI
Occurs within 30 days after the operation, AND
Involves only the skin or subcutaneous tissue of the incision, AND
At least one of the following:
Purulent drainage from the superficial incision
Organisms isolated from an aseptically obtained culture or nonculture-based microbiologic testing method of fluid or tissue from the superficial incision or subcutaneous tissue
Superficial incision that is deliberately opened by a surgeon, attending physician, or other designee when the patient has at least one of the following signs or symptoms: pain or tenderness, localized swelling, erythema, or heat unless the incision is culture negative
Diagnosis of superficial incisional SSI by the surgeon or attending physician or other designee
Deep incisional SSI
Occurs within 30 or 90 days after the operation according to NHSN’s table of operative procedures, AND
Involves deep soft tissues (e.g., fascial and muscle layers) of the incision, AND
At least one of the following:
Purulent drainage from the deep incision
A deep incision spontaneously dehisces or is deliberately opened by a surgeon when the patient has at least one of the following signs or symptoms: fever, localized pain or tenderness unless the site is culture negative
An abscess or other evidence of infection involving the deep incision that is detected on gross anatomic or histopathologic examination, or imaging test
Occurs within 30 or 90 days after the operation according to NHSN’s table of operative procedures, AND
Involves any part of the body deeper than the fascial/muscle layers (e.g., organs or spaces) that is opened or manipulated during the operative procedure, AND
At least one of the following:
Purulent drainage from a drain that is placed into the organ/space
Organisms isolated from a culture or non culture based microbiologic testing method of fluid or tissue in the organ/space
Organisms isolated from an aseptically obtained culture of fluid or tissue in the organ/space
An abscess or other evidence of infection involving the organ/space that is detected on gross anatomical or histopathologic examination, or imaging test
Meets at least one criterion for a specific organ/space infection site specified by NHSN
SSI , surgical site infection.
The risk of infection increases once the site has been contaminated with greater than 10 5 organisms per gram of tissue. The bacterial burden necessary to cause infection is significantly reduced when foreign material is in place (i.e., only 100 staphylococci per gram of tissue when introduced on silk sutures). Risk is also proportional to the toxins produced by the specific pathogen because these agents can facilitate host invasion, damage tissues, and interfere with host defenses.
The pathogens responsible for SSIs have not significantly changed over time. Table 28.1 lists the distribution of pathogens associated with SSIs. Staphylococcus aureus, Escherichia coli, coagulase-negative staphylococci, and Enterococcus faecalis represent nearly 50% of the pathogens associated with SSIs. S. aureus is the most common SSI pathogen for most types of surgery, but E. coli is more prevalent in abdominal surgery and Enterococcus species are most prevalent in transplant surgery.
|Pathogen||No. of pathogens||% of pathogens|
|Other Enterococcus species||6410||4.3|
|Group B streptococci||1879||1.3|
Sources of Pathogens
The primary source of SSI pathogens is the endogenous flora of the patient’s skin, mucous membranes, or hollow viscera. When the mucous membrane or skin is incised, the exposed tissues are at risk of contamination with endogenous flora. These organisms are usually aerobic gram-positive cocci (e.g., staphylococci). When an organ system is entered, endogenous flora specific to it may be the source of the pathogen (e.g., enteric flora such as E. coli or other gram-negative rods when bowel surgery is performed).
Surgical pathogens can also be derived from exogenous sources. Examples include surgical personnel (especially members of the surgical team), the OR environment (including air), and materials on the sterile field (such as instruments, equipment, containers) during an operation. Exogenous flora are primarily aerobes, especially gram-positive organisms (e.g., staphylococci and streptococci). Although S. aureus is usually from an endogenous source, evidence suggests exogenous pathways as well. Fungal SSIs are infrequent but can be endogenously or exogenously derived. Nevertheless, there are over two dozen reports of Candida infections in prosthetic joints, and a growing number of studies report Candida infections after cardiac surgery. Although these infections are infrequent, they are associated with serious problems, including a greater than 50% mortality.
A risk factor is a characteristic statistically associated with, although not necessarily causally related to, an increased risk for a particular outcome. Risk factors for developing an SSI after surgery can be broadly separated into preoperative, intraoperative, and postoperative settings and relate to patient, procedure, or facility factors ( Table 28.2 ). Nonmodifiable patient factors include increasing age, recent radiotherapy, and preexisting or history of skin or soft tissue infection. Potentially modifiable patient risk factors include glycemic control, alcohol, smoking status, malnutrition, obesity, and immunosuppression. Procedure-related factors include emergency surgery, surgical complexity, and wound classification. Facility risk factors include inadequate ventilation, increasing OR traffic, and inappropriate sterilization of equipment. In this section, preoperative, intraoperative, and postoperative preventative strategies for SSI will be examined in further detail.
Prevention of Surgical Site Infection
Diabetes Status and Control
Diabetes mellitus is a well-known risk factor for adverse medical events. Historically, increased risk for infection is thought to result from a combination of the long-term effects of hyperglycemia (e.g., macrovascular and microvascular disease) and the poor wound healing associated with neutrophil, complement, and antibody dysfunction. However, more recent data linking long-term blood glucose control and SSI risk have been mixed. A retrospective Veterans Affairs National Surgical Quality Improvement Program (VA NSQIP) study reported that an elevated Hgb A1c (marker of long-term glucose control) is associated with increased risk of postoperative infections and that Hgb A1c less than 7% was significantly associated with increased infectious complications. However, subsequent studies using multivariable analysis suggest that perioperative hyperglycemia, as opposed to elevated Hgb A1c, is associated with decreased SSI risk. Interestingly, several studies show that perioperative hyperglycemia increases the risk of SSI in both diabetic and nondiabetic patients. These studies suggest that short-term glucose control perioperatively may be more important than long-term Hgb A1c control in preventing SSIs.
Smoking is another well-known risk factor for postoperative infectious complications. The etiology is complex but probably mediated through three principal mechanisms: (1) tissue perfusion and oxygenation, (2) impairment of inflammatory cell functions and oxidative bactericidal mechanisms, and (3) attenuation of proliferative responses including reduced fibroblast migration and collagen synthesis and deposition. The effect of smoking is especially pronounced in cases in which foreign materials or prosthetics are implanted. The negative effect of smoking on SSI risk has been demonstrated across all surgical specialties, with current smokers carrying the highest risk followed by former smokers. The fact that former smokers have a higher risk of SSI compared with those who have never smoked demonstrates that the detrimental effect of smoking is prolonged or possibly even irreversible. Studies have shown that inflammatory cell response and bactericidal mechanisms improve after 4 weeks of abstinence from smoking, but impairment of proliferative responses may persist. Nevertheless, smoking cessation has been shown to be effective in reducing SSI risk and patients should be counseled to refrain from smoking for a minimum of 4 to 6 weeks prior to elective surgery. The effect of nicotine replacement therapy on wound microenvironment and healing is still poorly understood, but there is no evidence to suggest detrimental clinical effects on postoperative outcomes. Current opinion supports the use of nicotine replacement therapy as an aid to smoking cessation before surgery.
Preoperative malnutrition is a known risk factor for poor outcomes following surgery. Nutritional factors play critical roles in regulating metabolic pathways and immune system functions. A multicenter study found that preoperative hypoalbuminemia was an independent risk factor for SSI development after abdominal surgery. This effect has also been shown in many other types of surgeries. However, there is no consistent evidence for malnutrition screening and nutritional optimization prior to surgery. One Cochrane systematic review evaluated nutritional supplementation in elderly patients recovering from hip fracture that concluded that there is overall low-quality evidence to support nutritional interventions before or soon after surgery to prevent infectious complications.
Preoperative Bathing and Showering
Preoperative antiseptic shower or bath reduces skin bacteria colonization and decreases the risk of contamination at the surgical site. In 1980, Cruse and Foord reported nearly double the SSI rates among patients who did not shower (2.3%) compared with those who showered with chlorhexidine (1.3%). Multiple subsequent studies have found that showering with chlorhexidine-containing products lowered SSI rates. However, a recent Cochrane systematic meta-analysis of randomized controlled trials comparing preoperative bathing with chlorhexidine did not find a statistically significant reduction in SSIs compared with placebo controls. The result may be in part a result of the highly variable surgical patient population and lack of standardized bathing protocols. There is some evidence to suggest that chlorhexidine needs to dry on the skin for maximal effect and repeated applications are superior to a single shower. A recent randomized study showed that a standardized protocol of two or three sequential showers with 4% chlorhexidine gluconate with a 1-minute pause before rinsing resulted in maximal skin surface concentration. Although the evidence for preoperative bathing as an independent practice is inconclusive, it is important to note that preoperative bathing as part of a larger bundle has been shown to be beneficial in reducing SSIs.
MRSA Screening and Decolonization
Nasal carriage of S. aureus has been known as a risk factor for SSI for more than half a century. In 1959, Williams reported an increased risk of wound infection in patients with preoperative nasal carriage of S. aureus and Weinstein found that patients with preoperative colonization of nasal pathogens were more than twice as likely to acquire an infection than those patients with negative nasal cultures. Over the past two decades, many studies have repeatedly demonstrated the association of nasal S. aureus colonization with higher risk of both methicillin-resistant S. aureus (MRSA) and overall SSI among surgical patients. Unfortunately, in the same time frame, the prevalence of MRSA has dramatically increased with current incidence of positive MRSA screen at almost 7%.
The use of MRSA bundles, including screening, decolonization, contact precautions in the hospital, and vancomycin-containing antibiotic prophylaxis, have been shown to decrease SSI rates. Many decolonization protocols have been developed and no single protocol is considered standard and supported by literature. Although a Cochrane systematic review demonstrated that the use of nasal mupirocin alone reduces S. aureus infection, a typical decolonization protocol includes the use of 2% nasal mupirocin twice daily for 5 days and bathing with chlorhexidine gluconate at days 1, 3, and 5 preoperatively. Regardless of the exact components of the protocol, there is evidence to suggest that the decolonization must occur close to the time of surgery to be effective. Routine treatment of all patients and personnel with nasal carriage of MRSA has been carried out in some parts of Europe and Australia and has been proposed in the United States. However, several institutions have found that mupirocin resistance increased with this strategy. At this time, the American Society of Health System Pharmacists recommends screening and nasal mupirocin decolonization for all patients undergoing total joint replacement and cardiac procedures. For all other procedures, hospitals should evaluate their SSI and MRSA rates to determine whether implementation of a screening program is appropriate.
Preoperative bowel preparations for colorectal surgery include the use of mechanical bowel preparation (MBP) alone, oral antibiotics alone, or a combination of both. Although bowel preparations have been shown to be beneficial in reducing SSIs, concern has been raised about potential physiologic derangements related to dehydration that may prolong postoperative recovery. Practice patterns with respect to bowel preparations have evolved over time, but recently they have come full circle to support the use of a combination of MBP and oral antibiotics. A 2011 Cochrane systematic review including 18 randomized studies and 5805 patients did not find statistically significant differences between MBP alone and no MBP in terms of wound infections. Similarly, oral antibiotics or IV antibiotics alone are not effective. However, multiple recent studies show that use of a combination of both mechanical and oral antibiotic bowel preparations results in lower rates of SSI, anastomotic leak, and Clostridium difficile infection.
Asepsis and Surgical Technique
Asepsis is defined as the freedom from infection and the prevention of contact with any microorganism that could cause infection. Aseptic technique refers to the practices that are used by the surgical team to prevent infection during medical procedures. The basic principles of aseptic technique prevent contamination of the open wound, isolate the operative site from the surrounding unsterile physical environment, and create and maintain a sterile field in which the surgery can be performed. Many factors come into play to affect asepsis in the OR including the surgical scrub, appropriate gowning and ungowning, gloving technique, site preparation to reduce the normal flora of the patient, hair removal if necessary, and surgical draping. Excellent surgical technique is critical to reducing the risk for SSI and encompasses preventing hypothermia, maintaining hemostasis, handling tissues correctly, preserving blood supply, avoiding entries into a hollow viscus, removing devitalized tissue, placing drains appropriately, suturing appropriately, eradicating dead space, and managing the postoperative wound.
Although the origin of the practice of removing hair from the operative site has not been clearly documented, this surgical practice dates back to at least the 1850s at Bellevue Hospital in New York City and has been an established practice since the beginning of the 20th century. Razor shaving is associated with disruption of skin integrity because of microscopic cuts and abrasions that occur on the skin surface, liberating resident dermal bacteria into the operative field, and making the skin environment more favorable to bacterial proliferation. Seropian and Reynolds conducted the first prospective randomized study to challenge this traditional practice and found that SSI rate was nearly 10 times higher when hair was removed by razors (5.6%) compared with depilatory use or no hair removal (0.6%). A landmark 10-year prospective study found that the SSI rate was higher when hair was removed by electric clippers (1.4%) and highest when hair was removed by razors (2.5%) compared with no hair removal (0.9%). As such, hair removal is only recommended when the hair will interfere with surgery and razors are no longer recommended except in the scrotal area or the scalp after traumatic injury. The timing of hair removal is also important. Hair removal immediately prior to the operation is associated with decreased SSI rates when compared with hair removal within 24 hours preoperatively. The Guideline for Prevention of Surgical Site Infection advises that if hair is to be removed, it should be done so immediately before surgery and preferably with electric hair clippers.
The primary aim of patient skin antisepsis is to kill or incapacitate microorganisms and to reduce the risk of postoperative infection. Although there is general consensus that skin preparation is necessary prior to incision, the active ingredient in the scrub solution is the subject of debate. Five commercially available antimicrobial ingredients in the United States are approved antiseptic agents for surgical site disinfection: alcohols, chlorhexidine gluconate, iodine/iodophors, parachlorometaxylenol (PCMX), and triclosan. Historically, antiseptic agents progressed from the era of alcohol and carbolic acid to hexachlorophene and PCMX, then to povidone iodine, followed by chlorhexidine gluconate agents. Chlorhexidine gluconate, iodophors (e.g., povidone-iodine), and alcohol-containing products are currently the most commonly used agents, but there have been no well-controlled studies to determine the superiority of any agent. Chlorhexidine gluconate and iodophors have broad spectra of antimicrobial activity. Compared with iodophors, chlorhexidine gluconate has a greater microflora reductive effect, greater residual activity after a single application, and is not activated by blood or serum proteins. However, most randomized trials comparing chlorhexidine-based with iodine-based antiseptics have been underpowered to detect differences in SSI rates. Current evidence suggests that alcohol-based preparations are more effective in reducing SSI than aqueous preparations. Alcohol-based solutions have the most effective and rapid-acting bactericidal effect, but this benefit is limited by its lack of persistent antimicrobial effect. Some newer antiseptic solutions attempt to prolong the bactericidal activity in alcohol-based solutions with the addition of iodine or chlorhexidine. Although there is some evidence that chlorhexidine-isopropyl alcohol is superior to iodine-containing solution plus alcohol in preoperative skin flora decontamination, no study has convincingly demonstrated its superiority with regard to SSIs. Based on current evidence, alcohol-based antiseptics should be used when available. In the absence of alcohol preparations, chlorhexidine might be superior to iodine.
Surgical Hand Scrub
Surgical hand scrubs have been known to play a vital part in preventing surgical site infections for many years, beginning with the pioneering work of Ignaz Philipp Simmelweiss and Joseph Lister in the 1860s. Six commercially available antimicrobial ingredients in the United States are approved antiseptic agents for surgical hand antisepsis: alcohols, chlorhexidine gluconate, iodine/iodophors, PCMX, hexachlorophene, and triclosan. Although the data on the efficacy of microbial killing by these antiseptics demonstrate decreased bacterial colony counts on hands, the impact of the choice of scrub agent on SSI risk has not been evaluated. Several studies have found that alcohol-based antiseptics are more effective than povidone-iodine or chlorhexidine in reducing microbial counts. Historically, they were less frequently used in the United States because of concerns about flammability and drying of skin. 101 However, alcohol-based preparations for surgical hand antisepsis are gaining popularity because they are waterless, involve less scrub time, have a broad spectrum of activity, and do not require brushes. Chlorhexidine gluconate is a popular choice because of the persistence of its effects. It has a strong affinity for skin and remains active for over 6 hours and is not activated by blood or serum proteins. In a study evaluating residual activity following hand disinfection, the greatest sustained activity was achieved by alcoholic chlorhexidine. A recent Cochrane systematic review found that alcohol scrubs reduce colony-forming units (CFUs) compared with aqueous scrubs and that chlorhexidine gluconate scrubs reduce CFUs compared with povidone-iodine scrubs. However, the clinical relevance of this surrogate outcome on SSI risk is unclear and there is an overall low quality of evidence to support any one antiseptic over another.
Factors other than the choice of antiseptic agent influence the effectiveness of the surgical scrub, such as scrubbing technique, duration of scrub, condition of the hands, and techniques used for drying and gloving. Surgical hand antisepsis protocols have traditionally required scrubbing with a brush or sponge, but this practice is damaging to the skin and results in increased shedding of bacteria from the hands. Data now suggest that neither a brush nor a sponge is necessary to reduce bacterial counts on the hands to acceptable levels, especially when alcohol-based products are used. With regards to duration of scrub time, studies suggest that a scrub time of 2 or 3 minutes is as effective as the longer scrub time in reducing hand bacterial colony counts. Recently, waterless surgical scrub formulations have become commercially available. Studies show that waterless chlorhexidine scrub is as effective as traditional water-based scrubs and is acceptable in accordance with each product’s instructions.
Appropriate surgical attire helps contain bacterial shedding and promotes environmental control within the OR. Surgical attire typically refers to reusable scrubs consisting of pants and shirt, and sterile gowns. The term can also be extended to the disposable masks, gloves, surgical caps and hoods, and shoe covers that are utilized in the OR. Experimental data show that live microorganisms are shed from hair, exposed skin, and mucous membranes, but there are no well-controlled clinical studies evaluating the effect of surgical attire on SSI risk.
Surgical scrubs consist of pants and a shirt. Policies for laundering, wearing, covering, and changing scrubs vary greatly across institutions. Recently, many formerly acceptable practices, such as laundering scrubs at home and wearing scrubs outside the operating suite, have been called into question. However, there are no well-controlled studies evaluating these practices as an SSI risk factor. Similarly, an acceptable form of surgical caps has been a topic of controversy in recent years. The rationale for surgical caps is to reduce contamination of the surgical field by organisms shed from the hair and scalp. However, no data exists comparing cloth versus disposable hats and skull caps versus bouffant hats. In response to these debates, a task force convened by the American College of Surgeons (ACS) Board of Regents released new guidelines on surgical attire in 2016. These guidelines are based on professionalism, common sense, decorum, and available evidence. They recommend that clean and appropriate professional attire (not scrubs) be worn during all patient encounters outside the OR. OR scrubs should not be worn at any time outside the hospital perimeter. If they are worn outside the OR within the hospital, they should be covered with a clean lab coat or appropriate cover up. Scrubs and hats should be changed at least daily or after dirty or contaminated cases before subsequent cases, even if not visibly soiled. Visibly soiled scrubs from any procedure should be changed as soon as feasible and before speaking with family. Earrings and jewelry worn on the head or neck should be removed or appropriately covered during procedure and the mouth, nose, and hair should be covered during all invasive procedures.
Gowns and Drapes
The use of sterile gowns and drapes is indicated to isolate the sterile field from contamination because they provide a physical barrier between the sterile field and the surrounding sources of microbial contamination such as skin and hair. Regardless of the many materials used for gowns and drapes, the items should be impermeable to liquids and viruses. To meet the standards of the American Society for Testing Materials, the fabrics must be reinforced with films, coatings, or membranes to prevent breakthrough of fluids. Because such materials create increased body heat and may be uncomfortable, surgeons and staff must decide which materials should be selected for their practice.
Antimicrobial prophylaxis refers to a short course of an antibiotic administered prior to the surgery. The goal of antimicrobial prophylaxis is to reduce the number of organisms that could contaminate the operative site to a level that will not overwhelm host defenses. As early as 1961, it was shown that contaminants, including S. aureus , can be recovered from the operative site prior to closure. Burke demonstrated that prevention of SSI required that antibiotics be at an effective concentration in the tissue at the time of contamination. In 1969, Polk and Lopez-Mayor showed decreased rates of wound and intra-abdominal sepsis among patients who received antimicrobial prophylaxis prior to elective gastrointestinal tract surgery. Systemic antibiotics given after the contaminating event had no appreciable effect on the natural history of infection. For antimicrobial prophylaxis to be fully effective, an appropriate antimicrobial agent should be selected based on the type of surgery and the most common SSI pathogens for that surgery. Optimal prophylaxis depends on adequate concentrations being present in the serum, tissue, and wound during the entire time that the incision is open and at risk of contamination. The agent should be active against all potential contaminants and should have the least effect on the normal flora of the body.
There are limited published data on the optimal dosing of antimicrobial prophylaxis. Agents should be administered based on the patient’s weight. In a study of obese patients undergoing gastroplasty, patients who received 1 g of cefazolin had blood and tissue levels of cefazolin consistently below the minimum inhibitory concentration for gram-positive and gram-negative organisms and had higher incidence of SSI compared with patients who received 2 g. Studies also support redosing with antibiotics during surgery to maintain adequate tissue levels based on the agent’s half-life or for every 1500 mL estimated blood loss.
The initial dose of antibiotic should be infused so that its bactericidal concentration is established in serum and tissues by the time the skin is incised and so that it remains at a therapeutic concentration until the incision is closed. Classen found that SSI rates ranged from 0.6% to 3.8% depending on the timing of the infusion. The highest rates were seen when antibiotics were infused more than 2 hours before and again 3 hours after the incision. Rates were lowest at 0.6% among patients who were infused within 2 hours prior to incision. A more recent trial demonstrated similar results where SSI risks were lower with shorter interval between antibiotic infusion and surgical incision. However, other studies indicate that no statistically significant differences in SSI with strict administration windows. In 2003, the Medicare National Surgical Infection Prevention Project (SIPP) committee reviewed all published surgical antimicrobial prophylaxis guidelines and concluded that the infusion of the first antimicrobial dose should begin within 1 hour before incision or within 2 hours for fluoroquinolones or vancomycin. There was no consensus that the infusion must be completed before incision.
Special Considerations: MRSA Prophylaxis
The routine use of vancomycin for antimicrobial prophylaxis is not recommended for any kind of surgery. However, CDC guidelines suggest that vancomycin can be considered in certain clinical situations, such as when a cluster of MRSA infections has been detected. The threshold to support the decision to use vancomycin has not been scientifically defined. Additionally, there is no evidence that routine use of vancomycin will result in fewer SSIs than when other agents are used, even in institutions with perceived high rates of MRSA infection. A study at an institution with a perceived high rates of MRSA infections randomized cardiac surgery patients to cefazolin or vancomycin and found no statistically significant differences in SSI rates. However, cefazolin-treated patients who later developed an SSI were more likely to be infected with MRSA, and vancomycin-treated patients were more likely to be infected with methicillin-susceptible S. aureus . A more recent study similarly found that use of vancomycin alone in MRSA-negative patients was associated with a higher risk of methicillin-sensitive S. aureus SSI. Studies also indicate that lack of vancomycin prophylaxis is not associated with MRSA SSI risk. Conversely, in patients who are MRSA-negative preoperatively, treatment with vancomycin prophylaxis is a risk factor for conversion to MRSA-positive status. For these reasons, routine administration of vancomycin antibiotic prophylaxis in MRSA-negative patients is not recommended. Vancomycin might be considered an appropriate agent in patients known to be colonized by MRSA. According to the recent Society for Health-care Epidemiology of America guidelines, the colonization status of patients at high risk of carriage of MRSA should be routinely determined at the time of admission.
The concept of using a physical barrier to cover the surgical wound edges has been well-studied over the decades. However, data linking wound protectors with reductions in SSI are mixed. The ROSSINI (Reduction of Surgical Site Infection Using a Novel Intervention) trial was a large, multicenter randomized trial evaluating wound protector use in patients undergoing laparotomy for any emergency or elective procedures and failed to demonstrate significant benefit in SSI reduction. However, many other prospective, randomized trials have demonstrated substantial reductions in SSI rate with the use of plastic wound edge protectors. One meta-analysis pooled data from six RCTs and reported a significant decrease in SSI rates with wound protector use. Although the evidence for wound protector use is mixed, their use is generally supported and their benefit may be more pronounced in more defined patient populations, such as patients undergoing elective colorectal surgery.
Inflammation of the surgical site because of the presence of a foreign body, whether it be a prosthesis, a drain, or suture material, can increase the risk of infection. Extensive research compares different types of suture material and infection risk. In general, monofilament sutures are associated with the lowest infection rates. Recently, numerous studies have evaluated the effect of antibiotic sutures on SSI and have found decreased SSI rates with use of triclosan antibiotic sutures compared with standard sutures. These findings are confirmed by systematic review and meta-analysis on the subject.
As previously described, all wounds can be classified into four major categories: clean, clean/contaminated, contaminated, and dirty/infected. This classification of the degree of contamination in the surgical site has become the traditional system for predicting infection risk and for recommending the type of closure. Classically, primary closure is recommended for clean and clean/contaminated wounds and delayed primary closure or open wound management are recommended for contaminated and dirty wounds. A prospective randomized trial that compared primary closure with delayed primary closure reported lower wound infection rate in the delayed primary closure group. However, a systematic review evaluating eight randomized clinical trials comparing primary closure with delayed primary closure concluded that all studies were at high risk of bias with marked deficiencies in study design and outcome assessment. Although the studies reported reduced SSI risk with delayed primary closure, the effect was no longer significant after accounting for heterogeneity. In the setting of damage-control laparotomy, one study found that primary closure was associated with an increased risk of intra-abdominal SSI compared with open wound management; however, they also found that 85% of primary closure patients did not develop an SSI and were spared the morbidity of managing an open wound.
Hypothermia causes numerous adverse outcomes, including morbid myocardial events, coagulopathy with increased blood loss and transfusion requirement, postoperative wound infections, and prolonged hospitalization. The primary connection between thermoregulation and postsurgical resistance to infection is that hypothermia triggers thermoregulatory vasoconstriction, which, in turn, decreases tissue oxygenation. This effect was demonstrated as early as 1996 in a randomized, double-blind, controlled trial, which showed that warming patients for at least 30 minutes preoperatively significantly reduced SSI rates in colorectal surgery. The benefit of perioperative warming has been replicated in multiple randomized controlled trials in both short and long surgical cases. For longer cases, ongoing temperature monitoring and warming measures intra- and postoperatively are indicated.
Perioperative Supplemental Oxygen
There is general support for the use of supplemental oxygen in the perioperative setting in patients with normal pulmonary function. Although some randomized trials have found no benefit or even potentially deleterious effects of supplemental oxygen, most demonstrate that use of supplemental oxygen with 80% FiO 2 (fraction of inspired oxygen) during and after general anesthesia is beneficial compared with 30% FiO 2 . These findings were confirmed in a meta-analysis that concluded that supplemental oxygen led to a significant reduction in SSI risk.
Perioperative Glycemic Control
Although many of the long-term effects of diabetes cannot be reversed, evidence suggests that improving glucose control can improve immunologic function and postoperative outcomes. In fact, short-term glycemic control in the perioperative setting is arguably more important than long-term diabetic control in preventing SSIs. There appears to be a dose-response relationship between serum glucose level and SSIs, with patients with serum glucose of less than 130 mg/dL with the lowest SSI rate. Interestingly, although diabetic patients had higher rates of adverse events compared with nondiabetic patients in general, perioperative hyperglycemia posed a greater risk of adverse events in nondiabetic patients compared with diabetic patients. The authors hypothesized that this paradoxical effect may be a result of the underuse of insulin in nondiabetic patients and the higher level of tolerance of hyperglycemia in diabetic patients. Multiple randomized trials also demonstrated that strict glycemic control with glucose targets in the 100 to 150 mg/dL range is superior to liberal glycemic control. However, target rates below 110 mg/dL are associated with adverse outcomes, probably related to hypoglycemic episodes, without incremental benefit in reducing SSI risk. In general, perioperative management of glycemic control to maintain glucose levels between 110 and 150 mg/dL is considered acceptable for SSI prevention.
The OR, a controlled environment designed for the performance of surgical procedures, is the most highly regulated of all the patient service areas in the hospital. Its operation and maintenance are governed in the United States by the state department of health, the Joint Commission, recommendations from the CDC, the American Institute of Architects, and clinical practice guidelines developed by professional organizations such as the American College of Surgeons, the American Society of Anesthesiologists, and the Association of Operating Room Nurses. Together, these associations and organizations have outlined strict controls for the design and mechanical function of the OR.
Microorganisms in the air of the OR can be a potential source of surgical wound contamination. Multiple case studies have traced local epidemics of streptococcal SSIs to airborne transmission from OR personnel. Accordingly, the American Institute of Architects (AIA) has published guidelines for suggested ventilation parameters, including maintenance of temperature between 68°F (20°C) and 73°F (23°C), relative humidity between 30% and 60%, and 20 to 25 total air exchanges per hour (of which three must include fresh air). The CDC additionally recommends that airflow is directed and balanced to maintain positive pressure in the OR rooms with respect to corridors and adjacent areas, that air be introduced at the ceiling and exhausted near the floor, and that all HVAC systems have two filter beds in series.
Laminar airflow with high-efficiency particulate air (HEPA) filters has been shown to be useful primarily in orthopedic and implant surgery, where infection rates have been significantly reduced. Laminar airflow is designed to move particle-free air (ultraclean) over the sterile field at a uniform velocity of 0.3 to 0.5 μm/sec. The ultraclean recirculated air passes through HEPA filters and can be directed vertically or horizontally in the room. A large prospective, randomized multicenter study compared ultraclean air, antimicrobial prophylaxis, and ultraclean air combined with antimicrobial prophylaxis in total hip and knee replacement procedures. Although the results show that SSI rates decreased significantly with combination of antimicrobial prophylaxis and ultraclean air, similar effects were seen with only antimicrobial prophylaxis. A smaller study in spine surgery found a significant difference in SSI rates between ultraclean air and conventional groups even with use of prophylactic antibiotics. However, there is a minimal amount of data to support the use of ultraclean air in other nonorthopedic surgical areas.
Traffic within the operating suite must be controlled to ensure that only authorized personnel are entering restricted zones, to maintain the separation of clean from dirty areas, and to segregate clean equipment areas from contaminated workrooms. Surgical attire is required for moving around in semirestricted zones such as hallways, offices, or supply rooms that are adjacent to an OR, and a face mask is required when entering a room while a procedure is in progress. Attempts are made to limit the number of personnel in an OR during a procedure. Although there is evidence to suggest that the level of contamination is proportional to the number of personnel in the OR, it is unclear whether there is a link between increased number of personnel and increased SSI risk. Nevertheless, OR traffic should be controlled to decrease the bacterial load of the room by negating both air turbulence and bacterial shedding by personnel in the room.
Cleaning Environmental Surfaces
Environmental surfaces are not routinely implicated in surgical site infections. A randomized study compared cleaning ORs with Wet-Vac routinely between cases and only after contaminated cases and found significant differences in surface contamination but not in postoperative wound infections. However, OR telephones have been identified to be a potential reservoir for SSI-causing bacteria. In general, it is important to maintain a hygienic work environment in the OR. Routine cleaning of environmental surfaces should be performed between cases and at the end of the workday by hospital housekeeping staff trained in the proper techniques of OR cleaning. The decontamination process should begin at the highest level in the room (light tracks, ceiling fixtures) and progress downward to the level of shelves, tables, kickstands, and the floor. The Occupational Safety and Health Administration (OSHA) requires the environmental cleaning of all surfaces that have come in contact with blood or body fluids.
According to the CDC Guideline for the Prevention of Surgical Site Infections, there are no standardized parameters for the evaluation and comparison of microbial counts from air sampling or environmental cultures in ORs. Therefore, routine culturing of the OR environment is not recommended. Microbiologic sampling of the environment should take place only if an epidemiologic investigation is being conducted that implicates some areas as a potential source of an outbreak or a cluster of infections.
Sterilization of Surgical Instruments
Nondisposable surgical instruments must undergo physical cleaning followed by sterilization. Sterilization methods included steam under pressure, hydrogen peroxide gas plasma, vaporized hydrogen peroxide, ethylene oxide, or some other ethylene oxide-containing mixture. The most critical issue in instrument reprocessing is the required monitoring of the functional parameters (time, temperature, and pressure) of the sterilization process. Microbiologic and chemical testing of sterilization methods must be performed on a scheduled basis. Protection of the sterility of surgical instruments from time of sterilization until the time of use is critical. Sterilized equipment is generally wrapped in sterile coverings, which are routinely inspected for holes to identify inappropriately sterilized or contaminated contents. However, a study found that holes smaller than 1 cm were often missed by visual inspection, suggesting that more a rigorous technique may be required.
Flash sterilization is the processing of patient care items by steam sterilization when the item is intended for immediate use in a patient procedure. This situation arises when a critical instrument has been inadvertently dropped or another necessary piece of equipment is urgently needed. Flash sterilization is not appropriate for implantable items and it is not to be considered for the convenience or time-saving of the OR schedule. The problems with flash sterilization include a lack of biologic monitoring, an absence of protective packaging, an increased possibility of contamination, and shortened or minimal sterilization cycles. In steam sterilization, the parameters of time, temperature, and pressure are critical for adequately reprocessing a surgical instrument. The use of rapid biologic and chemical indicators has been evaluated and found to be acceptable. It is advisable, however, that flash sterilization be restricted to specific times and events.
Postoperative and PostDischarge Setting
The majority of the published evidence demonstrates that antibiotics after wound closure are unnecessary. A variety of clinical studies have found no difference in SSI rates when single-dose and multiple-dose regimens have been compared. Extended use beyond the operation may be associated with adverse events, such as Clostridium difficile colitis and the emergence of resistant bacterial strains. As such, the SIPP committee guidelines recommend discontinuation of antibiotics within 24 hours after the operation. An exception in which the optimal duration remains controversial is in cardiothoracic surgery. The American Society of Health-System Pharmacists (ASHP) recommends continuation of antimicrobial prophylaxis for up to 72 hours following cardiothoracic surgery, although this recommendation is based on expert opinion and the authors acknowledge that prophylaxis for less than 24 hours may be appropriate.
There is little guidance about when sterically dressed wounds can get wet by showering or bathing postoperatively. Although traditional teaching encourages waiting 48 hours after surgery before showering, but there are no data to suggest higher SSI rates with early showering (as early as 12 hours after surgery) compared with delayed showering (more than 48 hours after surgery). However, the only randomized trial on this topic was at high risk of bias and no conclusive evidence can be drawn. Timing of postoperative showering should be determined at the discretion of the operating surgeon.
The Joint Commission has identified nosocomial infection rates as an indicator of the quality of care in hospitals. Accredited hospitals must perform surgical site surveillance by systematic review of surgical patient charts, microbiology culture results, pharmacy data, radiology reports, communications from surgeons and nurses, and other sources of reliable information, such as pathology reports, autopsy reports, clinic visit reports, emergency room reports, and quality improvement databases operated by individual surgical services. To calculate meaningful SSI rates, data should be collected on all patients undergoing a surgical procedure of interest. Surveillance is best performed by an individual trained in hospital epidemiology and infection control (e.g., the infection control practitioner) who is guided by the practices of the Association for Professionals in Infection Control and Epidemiology. Monitoring of inpatient and outpatient surgeries should be performed with post-discharge surveillance. Currently there is no consensus on the best method of postdischarge surveillance and hospitals may choose methods that best fit their unique mix of procedures, personnel resources, and data needs. CDC’s National Health-care Safety Network (NHSN) collects and disseminates SSI rates compiled voluntarily from more than 17,000 health-care facilities representing all 50 states. The CDC uses the data that are reported by participating hospitals to estimate the magnitude of nosocomial infection problems in the United States and to monitor trends in infections and risk factors.
Prion Disease and the Operating Room
Prion diseases such as Creutzfeldt-Jakob disease (CJD), variant Creutzfeldt-Jakob disease (vCJD), and bovine spongiform encephalopathy (BSE) (or mad cow disease) represent a unique infection control problem because prions exhibit an unusual resistance to conventional chemical and physical decontamination methods. Because the CJD prion is not readily inactivated by conventional disinfection and sterilization procedures, and because of the invariably fatal outcome of CJD, the procedures for disinfection and sterilization have been both conservative and controversial for many years.
BSE is a progressive neurologic disorder of cattle first identified about three decades ago in Europe. By 2005, more than 184,000 cattle cases had been confirmed. When transmitted to humans through BSE-contaminated food, BSE produces the fatal neurodegenerative disease known as vCJD. There have been two cases of BSE in cows in the United States, one of which was known to have come from Canada. Three other cases of BSE-infected cows were identified in or linked to Canada. In April 2002, the Florida Department of Health and the CDC announced the occurrence of a likely case of vCJD in a Florida resident believed to have contracted it years before in England.
Iatrogenic cases of prion disease have occurred as a result of direct inoculation of prion particles during surgical procedures in the hospital setting. The first documented base occurred via an infected corneal transplant in 1974. More than 450 cases of iatrogenic transmissions have been identified worldwide in the past decade. Although the majority of these cases resulted from contaminated human growth hormone and cadaveric dura mater grafts, contaminated surgical instruments have been cited as a source. In 2001, the Joint Commission reported two incidents at accredited hospitals where 14 patients may have been exposed to CJD through instruments used during brain surgeries on patients of unsuspected cases of CJD. Between 1998 and 2012, 19 incidences of suspected CJD exposure via contaminated surgical instruments have been reported to CDC, of which two were in ophthalmologic surgeries and 17 were in neurologic surgeries.
Recommendations to prevent transmission of infection from medical devices contaminated by the CJD prion have been based primarily on prion inactivation studies. Commonly used methods for disinfection and sterilization may not adequately denature the prion particles. Recommendations for enhanced cleaning and sterilization (274°C for 18 minutes) of instruments used on patients suspected of having or confirmed to have CJD have been provided by the World Health Organization (WHO) and are cited in the APIC disinfectant guidelines. As prion diseases continue to increase in the United States and Europe, the potential for human-to-human iatrogenic spread of vCJD will probably increase. Infected individuals, like the rest of the population, will undergo medical and surgical procedures. Extending disinfectant protocols in the medical setting may be a strategy that deserves further investigation.