Impact Of MRSA On Various Types Of Surgical Site Infections (SSIs)
SSIs are the most common nosocomial infection in surgical patients. SSIs occur following approximately 2.6% of all operations and lead to increased cost and increased hospital length of stay (LOS). Previous reports document that SSIs are associated with 7.3 mean additional postoperative days at an additional cost of $3152 per patient.11-13 The impact of a methicillin-resistant Staphylococcus aureus (MRSA) SSI on patient outcome was examined in a recent single-institution study of 479 patients.14 Patients with an MRSA SSI had a greater 90-day mortality rate (adjusted odds ratio of 3.4; 95% confidence interval, 1.5-7.2), greater LOS (5 median additional days) and increased costs (1.19-fold increased hospital charges; P=0.03) compared with patients with a methicillin-sensitive S. aureus (MSSA) SSI (see Figure 3).14
SSIs range from those that are simple to manage, which entail opening the wound and prescribing a brief course of antibiotic therapy, to those that require repeat surgical intervention, removal of surgically placed prosthetic devices, and prolonged courses of antibiotic therapy. An SSI accounts for approximately 20% of all patients admitted to the hospital for an SSTI.
The Centers for Disease Control and Prevention (CDC) defines SSIs as those occurring within 30 days of an operation, and within 1 year if an implant was placed surgically. The CDC classification of SSI includes “incisional” (which may be “superficial,” involving only skin and subcutaneous tissue, or “deep,” involving fascia and muscle) and “organ/ space” infections, which involve any part of the anatomy other than the surgical incision, such as abdominal abscess or empyema.
Risk Factors For An SSI
Risk factors for an SSI include older age, diabetes, smoking, obesity, and prolonged preoperative stay, which is a surrogate marker of the severity of illness and comorbid conditions. Preoperative nasal colonization with S. aureus is associated with a significantly increased risk for SSI. Additional studies continue to investigate this important risk factor. Modifiable risk factors related to the conduct of the surgical procedure that can reduce the incidence of SSI include appropriate antimicrobial prophylaxis; maintenance of Figure 3. Impact of MRSA Surgical Site Infections on Patient Outcome
|  | | CI=confidence interval; LOS=length of stay; MRSA=methicillin-resistant Staphylococcus aureus; MSSA=methicillin-susceptible Staphylococcus aureus; OR=odds ratio. |
normothermia; skin antisepsis; replacement of shaving with clipping to remove hair; appropriate sterilization of instruments; avoidance of drains; avoidance of foreign material at the surgical site; excellent surgical technique; and minimization of operation duration.12
Previously, risk assessment for SSI was based solely on wound classification, whether the surgical site was clean, clean contaminated, contaminated, or dirty/infected. Clearly, the risk of SSI increases with increased contamination of the surgical site.12
The National Nosocomial Infections Surveillance (NNIS) System evaluated risk factors for SSI, and logistic regression analysis identified 3 independent variables associated with increased SSI risk: (1) American Society of Anesthesiology (ASA) score >2; (2) contaminated or dirty/infected wound classification; and (3) length of operation >75th percentile of the specific operation being performed.15 For example, a young, healthy patient with no NNIS risk factors undergoing an inguinal hernia repair (clean wound) has a 1% incidence of SSI. However, an older patient with diabetes and chronic renal insufficiency, and who requires a lengthy operation for perforated sigmoid diverticulitis with a contaminated wound, would have a 13.2% risk of SSI.
The performance of surgical procedures laparoscopically is associated with reduced SSI rates. This has recently led to a modification of the NNIS risk index for SSI. For biliary, gastric, and colon procedures that are performed laparoscopically, 1 NNIS risk factor is subtracted. Interestingly, the performance of appendectomy laparoscopically is associated with a decreased incidence of SSI only if the patient has no other NNIS risk factors. If the surgical procedure is lengthy or there is a contaminated surgical wound, the benefit of laparoscopy in reducing SSI is lost.
Microbiology Of SSIs
Factors that make SSIs difficult to avoid include a continued rise in antibiotic-resistant pathogens and increased numbers of patients with advanced age, chronic diseases, immunocompromised states, and transplant. Aerobic gram-positive cocci are leading causative pathogens of SSI nosocomial infections, including S. aureus, with the vast majority now MRSA, and coagulase-negative staphylococci (Staphylococcus epidermidis).16
Preventing SSIs
The CDC’s 12-step “Campaign to Prevent Antimicrobial Resistance” includes efforts to prevent infection, diagnose and treat infection, use antimicrobials wisely, and prevent transmission.17 For surgical patients, step 1 is to “prevent SSI.” Specific efforts to reduce an SSI described in this program include maintaining normoglycemia and normothermia, performing proper skin preparation, and administering prophylactic antimicrobials within 1 hour preceding incision and repeat dosing intraoperatively as needed. This information can be found on the CDC Web site at: http:// www.cdc.gov/drugresistance/healthcare/
surgery/12steps_surgery.htm.17
Antimicrobial Prophylaxis For Prevention Of SSIs
The mainstay of strategies for preventing SSIs is the administration of appropriate antimicrobial prophylaxis. The principles of antimicrobial prophylaxis for SSI prevention include using a drug active against expected microorganisms based on the surgical procedure performed. The goal of antimicrobial prophylaxis is to achieve high serum concentrations of the drug preoperatively (given within 1 hour before skin incision), and to maintain those levels during the operative period.12 Thus, antibiotics should be redosed for a long surgical procedure, significant blood loss, or fluid resuscitation. Antibiotics should not be given after the surgical wound is closed.
Strategies To Reduce MRSA SSIs
Due to the increasing MRSA rates in SSIs, the Medicare National Surgical Infection Prevention Project, in a 2003 advisory statement on antimicrobial prophylaxis for surgery, for the first time addressed issues related to the prevention of MRSA SSIs. First, it stated that it is probably appropriate to treat known carriers of MRSA with vancomycin for prophylaxis.18 However, there is no good evidence that vancomycin use is associated with reduced SSI rates. Finkelstein and colleagues performed a prospective, randomized study of 885 cardiac surgery patients randomized to antibiotic prophylaxis with cefazolin or vancomycin.19 No difference in SSI rates was identified, but patients who received cefazolin had a higher rate of SSI with MRSA, and those who received vancomycin had a higher rate of SSI with MSSA as the causative pathogen.19
The Society for Healthcare Epidemiology of America (SHEA) recently recommended routine surveillance cultures at the time of admission to the hospital for patients at high risk for carriage of MRSA. SHEA also noted that rates of MRSA colonization may be higher among patients who have previously spent 15 days in an institutional setting, including long-term or acute care centers.20
Clearly, excellent infection control is a mainstay in prevention of SSIs. Appropriate hand hygiene and cleansing of the surgical site, strict sterile technique in the operating room, and strict infection control practices are necessary for SSI prevention. Recent data suggest that chlorhexidine prep plus alcohol for surgical site preparation is superior to other surgical preps.21 Chlorhexidine has rapid and persistent antibacterial activity against gram-positive and gram-negative bacteria, and prevents regrowth of microorganisms on the skin for at least 48 hours.
Conclusion
MRSA is the leading causative pathogen in SSIs, and MRSA SSIs have been shown to be associated with adverse patient outcomes. Risk factors for a patient developing an SSI include older age, diabetes, smoking, obesity, prolonged preoperative stay, and malnutrition. Early treatment is therefore of the utmost importance and includes surgical incision and drainage, debridement of necrotic tissue, if present, as well as prompt initiation of appropriate empiric antibiotic therapy. Most importantly, strategies should be implemented in an effort to prevent an MRSA SSI. |
