Definition and Classification
Surgical-site infection (SSI) is a difficult term to define accurately because it has a wide spectrum of possible clinical features.
The Centers for Disease Control and Prevention (CDC) has defined SSI to standardize data collection for the National Nosocomial Infections Surveillance (NNIS) program. [8, 16] SSIs are classified into incisional SSIs, which can be superficial or deep, and organ/space SSIs, which affect the rest of the body other than the body wall layers (see the image below). These classifications are defined as follows:
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Superficial incisional SSI - Infection involves only skin and subcutaneous tissue of incision
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Deep incisional SSI - Infection involves deep tissues, such as fascial and muscle layers; this also includes infection involving both superficial and deep incision sites and organ/space SSI draining through incision
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Organ/space SSI - Infection involves any part of the anatomy in organs and spaces other than the incision, which was opened or manipulated during operation
Superficial incisional SSI is more common than deep incisional SSI and organ/space SSI. Superficial incisional SSI accounts for more than half of all SSIs for all categories of surgery. The postoperative length of stay is longer for patients with SSI, even when adjusted for other factors influencing length of stay.
History and Physical Examination
A report by the NNIS program [17] cited particular clinical findings as characteristic of the different types of SSI.
Superficial incisional SSI is characterized by the following:
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Occurs within 30 days after the operation
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Involves only the skin or subcutaneous tissue
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Includes at least one of the following: (a) purulent drainage is present (culture documentation not required); (b) organisms are isolated from fluid/tissue of the superficial incision; (c) at least one sign of inflammation (eg, pain or tenderness, induration, erythema, local warmth of the wound) is present; (d) the wound is deliberately opened by the surgeon; (e) the surgeon or clinician declares the wound infected
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Note: A wound is not considered a superficial incisional SSI if a stitch abscess is present; if the infection is at an episiotomy, a circumcision site, or a burn wound; or if the SSI extends into fascia or muscle
Deep incisional SSI is characterized by the following:
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Occurs within 30 days of the operation or within 1 year if an implant is present
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Involves deep soft tissues (eg, fascia and/or muscle) of the incision
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Includes at least one of the following: (a) purulent drainage is present from the deep incision but without organ/space involvement; (b) fascial dehiscence or fascia is deliberately separated by the surgeon because of signs of inflammation; (c) a deep abscess is identified by direct examination or during reoperation, by histopathology, or by radiologic examination; (d) the surgeon or clinician declares that a deep incisional infection is present
Organ/space SSI is characterized by the following:
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Occurs within 30 days of the operation or within 1 year if an implant is present
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Involves anatomic structures not opened or manipulated during the operation
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Includes at least one of the following: (a) purulent drainage is present from a drain placed by a stab wound into the organ/space; (b) organisms are isolated from the organ/space by aseptic culturing technique; (c) an abscess in the organ/space is identified by direct examination, during reoperation, or by histopathologic or radiologic examination; (d) a diagnosis of organ/space SSI is made by the surgeon or clinician
Examples of wound infections are shown in the images below.
Wound infection due to disturbed coagulopathy. This patient has a pacemaker (visible below right clavicular space) and had previous cardiac surgery (median sternotomy wound visible) for a rheumatic mitral valve disorder, which was replaced. The patient was taking anticoagulants preoperatively. Despite converting to low-molecular weight subcutaneous heparin treatment and establishing normal coagulation studies, she developed a postoperative hematoma with subsequent wound infection. She had the hematoma evacuated and was administered antibiotic treatment as guided by microbiological results, and the wound was left to heal by secondary intention.
Large ulceration in a tattoo. A 33-year-old man presented with a superficial ulceration about 4 weeks after a red tattoo on his forearm. Microbial swabs remained negative. His medical history was uneventful and he was in good general health. No reason for this uncommon reaction could be identified. Image courtesy of the National Institutes of Health.
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Wound infection due to disturbed coagulopathy. This patient has a pacemaker (visible below right clavicular space) and had previous cardiac surgery (median sternotomy wound visible) for a rheumatic mitral valve disorder, which was replaced. The patient was taking anticoagulants preoperatively. Despite converting to low-molecular weight subcutaneous heparin treatment and establishing normal coagulation studies, she developed a postoperative hematoma with subsequent wound infection. She had the hematoma evacuated and was administered antibiotic treatment as guided by microbiological results, and the wound was left to heal by secondary intention.
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Abscess secondary to a subclavian line.
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Definitions of surgical site infection (SSI).
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Factors that affect surgical wound healing.
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Large ulceration in a tattoo. A 33-year-old man presented with a superficial ulceration about 4 weeks after a red tattoo on his forearm. Microbial swabs remained negative. His medical history was uneventful and he was in good general health. No reason for this uncommon reaction could be identified. Image courtesy of the National Institutes of Health.
Tables
- Table 1. Pathogens Commonly Associated with Wound Infections and Frequency of Occurrence [8]
- Table 2: Surgical Wound Classification and Subsequent Risk of Infection (If No Antibiotics Used) [8, 10]
- Table 3. Recommendations for Prophylactic Antibiotics as Indicated by Probable Infective Microorganism Involved [8, 30]
- Table 4. Predictive Percentage of SSI Occurrence by Wound Type and Risk Index* [31]
- Table 5. American Society of Anesthesiologists (ASA) Classification of Physical Status [32]
- Table 6. Data Support Recommendations
Pathogen |
Frequency (%) |
Staphylococcus aureus |
20 |
Coagulase-negative staphylococci |
14 |
Enterococci |
12 |
Escherichia coli |
8 |
Pseudomonas aeruginosa |
8 |
Enterobacter species |
7 |
Proteus mirabilis |
3 |
Klebsiella pneumoniae |
3 |
Other streptococci |
3 |
Candida albicans |
3 |
Group D streptococci |
2 |
Other gram-positive aerobes |
2 |
Bacteroides fragilis |
2 |
Classification |
Description |
Infective Risk (%) |
Clean (Class I) |
Uninfected operative wound No acute inflammation Closed primarily Respiratory, gastrointestinal, biliary, and urinary tracts not entered No break in aseptic technique Closed drainage used if necessary |
< 2 |
Clean-contaminated (Class II) |
Elective entry into respiratory, biliary, gastrointestinal, urinary tracts and with minimal spillage No evidence of infection or major break in aseptic technique Example: appendectomy |
< 10 |
Contaminated (Class III) |
Nonpurulent inflammation present Gross spillage from gastrointestinal tract Penetrating traumatic wounds < 4 hours Major break in aseptic technique |
About 20 |
Dirty-infected (Class IV) |
Purulent inflammation present Preoperative perforation of viscera Penetrating traumatic wounds >4 hours |
About 40 |
Operation |
Expected Pathogens |
Recommended Antibiotic |
Orthopedic surgery (including prosthesis insertion), cardiac surgery, neurosurgery, breast surgery, noncardiac thoracic procedures |
S aureus, coagulase-negative staphylococci |
Cefazolin 1-2 g |
Appendectomy, biliary procedures |
Gram-negative bacilli and anaerobes |
Cefazolin 1-2 g |
Colorectal surgery |
Gram-negative bacilli and anaerobes |
Cefotetan 1-2 g or cefoxitin 1-2 g plus oral neomycin 1 g and oral erythromycin 1 g (start 19 h preoperatively for 3 doses) |
Gastroduodenal surgery |
Gram-negative bacilli and streptococci |
Cefazolin 1-2 g |
Vascular surgery |
S aureus, Staphylococcusepidermidis, gram-negative bacilli |
Cefazolin 1-2 g |
Head and neck surgery |
S aureus, streptococci, anaerobes and streptococci present in an oropharyngeal approach |
Cefazolin 1-2 g |
Obstetric and gynecological procedures |
Gram-negative bacilli, enterococci, anaerobes, group B streptococci |
Cefazolin 1-2 g |
Urology procedures |
Gram-negative bacilli |
Cefazolin 1-2 g |
At Risk Index |
Predictive Percentage of SSI |
0 |
1.5 |
1 |
2.9 |
2 |
6.8 |
3 |
13.0 |
*Hospital Infection Control Practices Advisory Committee (HICPAC) recommendations (partial) for the prevention of SSIs, April 1999 (non–drug based) |
|
ASA Score |
Characteristics |
1 |
Normal healthy patient |
2 |
Patient with mild systemic disease |
3 |
Patient with a severe systemic disease that limits activity but is not incapacitating |
4 |
Patient with an incapacitating systemic disease that is a constant threat to life |
5 |
Moribund patient not expected to survive 24 hours with or without operation |
Category |
Description |
Category IA |
Well designed, experimental, strong; recommended (category I*) clinical or epidemiological best practice; should be studies; adapted by all practices |
Category IB |
Some experimental, fairly strong; recommended (category II*) clinical or epidemiological best practice; should be studies and theoretical grounds; adapted by all practices |
Category II |
Fewer scientific supporting data; limited to specific nosocomial (category III*) problems |
No recommendation |
Insufficient scientific personnel judgment for use (category III*) supporting data |
*Previous nomenclature of 1992 CDC guidelines |
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