Surgical Site Infections
Ioana Chirca
Camelia E. Marculescu
There are more than 25 million surgical procedures performed every year in the United States, and surgical site infections (SSI) complicate 1% to 5% of cases.1 SSI increase the risk of death by 2- to 12-fold, length of hospitalization on average more than a week, and cost of treatment up to $60,000 depending on the type of SSI.2,3
DEFINITIONS
The clinical definition of an SSI in its simplest form is purulent drainage from a surgical incision site. This may or may not be accompanied by other local signs or symptoms of infection (swelling, redness, warmth) and may or may not be accompanied by a positive microbiologic culture. Because of this variation in clinical presentation and to better establish national benchmarks, the Centers for Disease Control and Prevention (CDC) has developed surveillance definitions for SSI. In general, a surgical site is monitored for 30 days for SSI if no implant is involved and for 12 months if an implant is utilized. SSIs are classified as superficial incisional, deep incisional, and organ/space.4
Superficial incisional SSI involves only the skin and subcutaneous tissue of the incision. Additionally, the patient needs to have at least one of the following: (1) purulent drainage from the superficial site, (2) organisms aseptically isolated from fluid or tissue in the superficial incision, and (3) at least one sign/symptom of infection (pain, localized swelling, erythema, warmth) and the superficial incision is deliberately opened by the surgeon and is culture positive or not cultured; culture-negative does not meet the criterion.
Deep incisional SSI involves deep soft tissues of the incision (fascia, muscles). Additionally, the patient needs to have at least one of the following: (1) purulent drainage from the incision but not from the organ/space component of the surgical site, (2) spontaneous dehiscence or deliberate opening of a deep incision with positive cultures or not cultured when the patient has fever or localized pain, and (3) abscess or other evidence of infection is found on examination, during reoperation, or by histopathologic or radiologic examination.
Organ/space SSI is when the infection involves any part of the body but excludes categories mentioned above—skin, fascia, and muscles at the incision site. Additionally, the patient needs to have at least one of the following: (1) purulent drainage from a drain placed through a stab wound into the organ/space, (2) positive aseptically obtained cultures from tissue or fluid in the organ/space, and (3) abscess or evidence of infection of the organ/space on examination, reoperation, and histopathologic or radiologic examination. If an organ/space infection drains through the incision (often via a sinus tract), this is classified as a deep incisional SSI.
EPIDEMIOLOGY
The microbiology associated with SSI has not significantly changed over the previous few decades with the most common pathogens being Staphylococcus aureus and coagulase-negative staphylococci (Table 34-1).5 Other important pathogens are Enterococcus spp., Pseudomonas spp., and other gram-negative bacteria. The site of surgery is generally the primary determinant of the organism responsible for the infection and depends on established colonizing organisms (e.g., staphylococcal predominance for orthopedic, cardiac, and vascular surgeries and gram negatives for abdominal surgeries). Antimicrobial resistance exhibited by some of these pathogens has been associated with poorer outcomes. Resistance also impacts antibiotic prophylaxis and empiric treatment of SSI. Surgeons and clinicians providing care for patients with SSI should be familiar with their local microbiology and resistance data. Recent CDC data report that approximately half of S. aureus SSI are methicillin resistant, 20% of enterococcal SSI are vancomycin resistant, and many gram-negative organisms causing SSI are resistant to fluoroquinolones and third-generation cephalosporins. Additionally, one needs to be aware of emerging SSI pathogens such as fungi, including invasive molds, and rapidly growing mycobacteria.
PATHOGENESIS AND RISK FACTORS
SSI is the result of complex interactions between multiple factors.
Microbial factors: Bacteria can reach the surgical wound by endogenous and exogenous contamination. The most frequent mechanism is by endogenous contamination from organisms that reside on the skin and in skin appendages as antiseptic measures cannot completely eliminate bacteria.6 Exogenous contamination is rare but has been reported such as colonization with S. aureus of operating room personnel and contamination of water sources or water-based solutions with organisms such as Legionella, Pseudomonas, or nontuberculous mycobacteria.7,8,9,10 Bacterial virulence factors such as increased adhesion to wound matrix components by S. aureus and coagulase-negative staphylococci, biofilm production, exotoxin production by staphylococci and streptococci, and endotoxin production by gram-negative organisms may also be important for SSI risk and pathogenesis.11,12,13,14 Also, it is intuitive that the higher the bacterial inoculum, the higher the risk of SSI and this served as the basis for classification of surgical wounds by the level of probable contamination (Table 34-2).15
Table 34-1 Major Pathogens Responsible for Surgical Site Infection5
Pathogen
Percentage of SSI
Staphylococcus aureus
30
Coagulase-negative staphylococci
13.7
Enterococcus spp.
11.2
Pseudomonas aeruginosa
5.6
Escherichia coli
9.6
Klebsiella pneumoniae
3
Acinetobacter, Serratia, Citrobacter
1 to 3
Candida spp.
2
Table 34-2 Wound Classification According to the Level of Contamination
Class
Type of Wound
Characteristics
I
Clean
Uninfected, primarily closed, drained with closed drainage
II
Clean-contaminated
Respiratory, urinary, gastrointestinal (GI), and genital tract are entered under controlled conditions.
III
Contaminated
Open, fresh wounds; procedures with major breaks in sterile techniques, gross spillage from GI tract
IV
Dirty-infected
Old, traumatic wounds; perforated viscus; preexisting clinical infection.
Adapted from Mangram et al. Guideline for prevention of surgical site infection, 1999. Centers for Disease Control and Prevention (CDC) Hospital Infection Control Practices Advisory Committee. Am J Infect Control 1999;27:97-132, with permission.
Patient characteristics: Age is not modifiable but has clearly been linked to the risk of developing an SSI, likely due to an increased incidence of other comorbid conditions.16 Nutritional status has been considered to be important in determining risk for SSI; however, recent studies have not identified malnutrition as an independent risk factor. Conversely, obesity has been linked to increased risk for SSI due to mechanical issues of increased body mass as well as likely underdosing of prophylactic antimicrobials. Hyperglycemia increases the risk for SSI. Current recommendations suggest a goal serum glucose <180 mg/dL.17 Smoking increases risk for SSI almost twofold, likely via vasoconstriction.18 Smoking cessation is advised at least 4 weeks prior to surgery.17 Nasal colonization with S. aureus has been reported as an independent risk factor for SSIs in some surgeries, including orthopedic procedures.19,20 Nasal colonization has also been associated with colonization at other body sites, and thus, it is recommended to administer chlorhexidine bathing in close proximity to the surgical procedure.17 Despite this recommendation, outcome data on SSI prevention have been mixed. Immunosuppressive medications have also been associated with increased risk of SSI, and if possible, they should be avoided in the perioperative period.21Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
