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Surgical Site Infection 99

the incision, that was opened or manipulated during an operation. At In addition to the above general factors, there are important
least one of the following is present: individual patient risk factors that may also affect the incidence
• purulent drainage from a drain that is placed through a stab wound of wound infection, such as body mass index (BMI), age, human
into the organ or space; immunodeficiency virus (HIV), and immune deficiency states.
• organisms are isolated from an aseptically obtained culture of fluid Pathophysiology
or tissue in the organ or space; SSI arises secondary to exogenous or endogenous bacterial contami-
nation at the time of the operative procedure. Bacterial proliferation
• an abscess or other evidence of infection involving the organ space
that is found on direct examination, during reoperation, or by histo- results in tissue reaction and outpouring of inflammatory cells, lead-
pathologic or radiologic examination; or ing to tissue destruction and pus formation. The presence of local
factors such as necrosis, haematoma, and dead space provide bacteria
• diagnosis of an organ space SSI by a surgeon or attending physician. with a milieu for growth, and the presence of other foreign bodies
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inhibits local tissue resistance. Microorganisms may contain or pro-
Risk Assessment duce toxins and other substances that increase their ability to invade a
Attempts have been made to derive a clinically useful index that will host, produce damage within the host, or survive on or in host tissue.
encompass the major factors influencing wound infection rate and thus Many gram-negative bacteria produce an endotoxin that stimulates
predict a patient’s risk of developing wound infection in the postopera- cytokine production. The cytokines can trigger a systemic inflam-
tive period. A multivariate index combining patient susceptibility and matory response syndrome that sometimes leads to multiple system
wound contamination was developed and tested during the CDC Study organ failure. 19
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on the Efficacy of Nosocomial Infection Control (SENIC). This Patient factors that may possibly increase the risk of an SSI
index involves the following four risk factors: include coincident remote site infections or colonisation, diabetes,
1. an operation that involves the abdomen; systemic steroid use, obesity (>20% ideal body weight), and poor
2. an operation lasting longer than 2 hours; nutritional status.
3. an operation classified as either contaminated, dirty, or infected; and Clinical Presentation
4. a patient having three or more discharge diagnoses. Nonspecific clinical signs mimicking infection frequently occur in
Each of these equally weighted factors contributes a point when the postoperative period, making the diagnosis difficult. These signs
present, so the risk index values range from 0 to 4. By using include wound erythema and induration secondary to lymphatic and
these factors, the SENIC index predicted SSI risk twice as well venous obstruction, fever, and leucocytosis. Most SSIs present from 3
as the traditional wound classification scheme alone. Because to 14 days postoperatively.
this index included discharge diagnoses, some modification and a Gram-positive SSIs tend to arise early (3 to 6 days) and are
prospective evaluation of the index became necessary before it could characterised by prominent local signs and symptoms. The wound is
be recommended for clinical use. A further modification of this index indurated, erythematous, and tender. Drainage is purulent and generous.
was therefore developed. This is the National Nosocomial Infection Systemic signs are usually mild and include low-grade fever and
1
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Surveillance (NNIS) index. The NNIS risk index is operation- irritability. Group A streptococcus SSI typically presents dramatically
specific and applied to prospectively collected surveillance data. 24 to 48 hours postoperatively with spreading cellulitis with distinct
The index values range from 0 to 3 points and are defined by three margins and lymphangitis. Drainage is scant and serous in nature.
1
independent and equally weighted variables. One point is scored for Systemic signs are prominent with high-grade fever and toxaemia.
each of the following when present: Gram-negative SSI tends to arise later, 7 to 14 days postoperatively,
and thus could present after discharge from hospital. Local signs are
1. a patient having an American Society of Anesthesiologists (ASA)
preoperative score of 3, 4, or 5; less pronounced. Systemic signs are, however, often more prominent,
with high-grade fever and tachycardia. Wound drainage, if present, is
2. an operation classified as either contaminated or dirty; and sero-purulent and may be foul smelling.
3. an operation lasting more than T hours, where T depends on the Local Features of SSI
operation being performed (T approximates the 50th percentile of the
Common local features of SSI include:
duration of a procedure and varies from 1 hour for an appendectomy
• pain and tenderness beyond what is expected for the nature of the
to 7 hours in organ transplant surgery).
surgery, and despite adequate analgesia;
The ASA class replaced discharge diagnoses of the SENIC risk
index as a surrogate for the patient’s underlying severity of illness • swelling, induration, and warmth;

(host susceptibility). It has the advantage of being readily available in
• shiny, erythematous skin; and
the chart during the patient’s hospital stay. Unlike SENIC’s constant
2-hour cut point for the duration of the operation, the operation-specific • purulent discharge.
cut points used in the NNIS risk index increase its discriminatory Systemic Features of SSI
power. Although their long-term usefulness in predicting postoperative
Common systemic features of SSI include:
wound infection is still being evaluated, preliminary reports have been
• pyrexia (≥37.8°C);
validating the usefulness of these indices in adult patients. There is
a need to validate these indices in paediatric patients before general • leucocytosis;
acceptance.
• tachycardia;
In a report on 322 sub-Saharan African children undergoing
operation, the SSI rate was 14.3% in clean incisions, 19.3% in clean- • tachypnoea;
contaminated incisions, 27.3% in contaminated incisions, and 60% in
• vomiting; and
dirty incisions. The degree of incisional contamination and a duration
of surgery ≥2 hours were important risk factors that were significantly • refusal to feed/anorexia (particularly in neonates and infants).
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associated with SSI.