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APIC Infection Control
and Applied Epidemiology
Principles and Practice
APIC Text of Infection
Control and Epidemiology
Surgical Site Infections Guidelines
Chapter 91
Jennifer White, Donald Fry, and Richard Howard
APIC Infection Control
and Applied Epidemiology
Surgical Site Infections
Jennifer White, Donald Fry, and Richard Howard
A. Overview
In the United States alone, approximately 27 million
surgical procedures are performed each year.1 The
Centers for Disease Control and Prevention’s (CDC’s)
National Nosocomial Infections Surveillance system,
which monitors and reports trends in nosocomial
infections in US acute care hospitals, has found that
surgical site infections (SSIs) are the third most
frequently reported nosocomial infection among
hospitalized patients.2 SSIs increase the length of
hospital stay by an average of 7.3 days and, in 1992,
added approximately $3152 to the hospital bill.3,4,5,6
Thus, it is important to develop an understanding of
the causes of SSIs and develop effective interventions
to prevent them.
B. Classification of Surgical Site Infections
In 1988, the CDC published a definition of surgical
wound infection that divided wound infections into
either incisional surgical wound infections or deep
surgical wound infection.7 This was revised in 1992,
changing the name surgical wound infection to surgical
site infection to emphasize the importance of specifying
the anatomical location involved in deep surgical
wound infections. The modifications made in 1992
have become the standard for classifying surgical site
infections. This classification scheme describes SSIs on
the basis of three anatomically distinct categories. These
are superficial incisional SSI, deep incisional SSI, and
organ/space SSI.8 In this scheme, infections are SSIs
if they occur within 30 days of the operative procedure
if no implant, and within 1 year if an implant is left
in place.8 (See also Appendix 91-A for detailed
surveillance definitions).9
1. Superficial incisional SSIs
a) Involve only the skin or subcutaneous tissue of
the incision.
b) Involves as least one of the following:
(1) Purulent drainage from the superficial incision.
(2) Organisms isolated from an aseptically
obtained culture of fluid or tissue from the
superficial incision.
(3) At least one of the following signs or
symptoms of infection: pain or tenderness,
localized swelling, redness or heat, and the
superficial incision is deliberately opened
by a surgeon, unless culture of the incision
is negative.
(4) Diagnosis of a superficial incisional SSI by
a surgeon or attending physician.
2. Deep incisional SSIs
a) Infection involves deep soft tissues of the incision.
b) Involves at least one of the following:
(1) Purulent drainage from the deep incision but
not from the organ/space component of the
surgical site.
(2) 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 (over 38°C), localized
pain or tenderness, unless culture of the
incision is negative.
(3) An abscess or other evidence of infection
involving the deep incision is found on direct
examination, during reoperation, or by
histopathologic or radiologic examination.
(4) Diagnosis of a deep incisional SSI by a
surgeon or attending physician.
3. Organ/space SSI
a) Involves any part of the anatomy other than the
incision, opened, or manipulated during the
operative procedure.
b) Specific sites are assigned in order to identify the
location of the infection (i.e., intraabdominal,
joint, bursa, etc.).
c) Involves at least one of the following:
(1) Purulent drainage from a drain placed through
a stab wound into an organ/space.
(2) Organisms isolated from an aseptically
obtained culture of fluid or tissue in the
organ/space.
(3) Abscess or other evidence of infection
involving the organ/space on direct
examination, during reoperation, or by
histopathologic or radiologic examination.
(4) Diagnosis of an organ/space SSI by a surgeon
or attending physician.
1
C. Classification of Surgical Wounds
Surgical wounds are classified on the basis of the extent
of contamination and increased risk of infection
according to the scheme developed by the National
Academy of Sciences and National Research Council.10
1. Clean wounds
a) Elective, primarily closed and undrained.
b) Nontraumatic, noninfected, including blunt,
nonpenetrating trauma.
c) No inflammation encountered.
d) No break in aseptic technique.
e) Respiratory, alimentary, genitourinary, or
oropharyngeal tracts not entered.
2. Clean-contaminated
a) Alimentary, respiratory, or genitourinary tracts
entered under controlled conditions and with no
unusual contamination.
b) Genitourinary tract entered in absence of
culture-positive urine.
c) Biliary tract entered in absence of infected bile.
d) Minor break in technique.
3. Contaminated
a) Open, fresh traumatic wounds.
b) Gross spillage from gastrointestinal tract.
c) Entrance into genitourinary or biliary tracts in the
presence of infected urine or bile.
d) Major break in surgical technique.
e) Incisions in which acute nonpurulent inflammation
is present.
4. Dirty and infected
a) Traumatic wound with retained devitalized tissue,
foreign bodies, fecal contamination, or delayed
treatment, or from a dirty source.
b) Perforated viscus encountered.
c) Acute bacterial inflammation with pus
encountered during operation.
D. Risk Factors for Postoperative
Wound Infection
1. Microbe-related risk factors
a) Load of bacteria introduced into the wound.
(1) Contamination with >105 microorganisms per
gram of tissue markedly increases the risk of
SSI while less contamination generally does
not produce infection.11 The presence of
foreign material markedly decreases the
number of microorganisms required to
cause an infection12,13.
b) Virulence of the bacteria contaminating the wound.
c) Elaboration of endotoxins.
d) Ability to resist host defenses.
e) Ability to adhere to wound surfaces/prosthetic
devices (i.e., slime producing coagulase-negative
Staphylococcus)14.
2. Host-related risk factors15
a) Define relation to wound infection.
(1) Morbid obesity16
(2) Extremes of age
(3) Prolonged preoperative stay
(4) Infection at other sites
(5) American Society of Anesthesiologists
(ASA) class
(6) Disease severity index (e.g., ASA score)
b) Likely relation to wound infection.
(1) Low albumin
(2) Malnutrition
(3) Nicotine use 17-18
c) Possible relation to wound infection.
(1) Cancer
(2) Diabetes mellitus16
(3) Immunosuppressive therapy
(4) Operation-related risk factors15,19-20
a) Surgical wound classification
b) Intraoperative microbial contamination
c) Antimicrobial prophylaxis
d) Preoperative shaving
e) Preoperative skin preparation
f) Thoroughness of surgical scrub
g) Duration of surgical procedure
h) Surgical technique
(1) Poor hemostasis
(2) Failure to obliterate dead space
(3) Tissue trauma
i) Low abdominal operative site
j) Prolonged hospital admission prior
to operation
k) Foreign material
l) Operating room ventilation
m) Instrument sterilization
E. SSI Risk Stratification
Through the years, various schemes for SSI risk
stratification have been developed.
1. In 1964, the National Academy of Sciences/National
Research Council cooperative study proposed a
scheme for SSI surveillance which was modified by
the CDC in 1982 and included the following:
a) At the end of the operation, a member of the
surgical team classified the patient’s wound as
either clean, clean-contaminated, contaminated,
or dirty and infected as defined above in
Section C.21,22
b) This strategy has several shortcomings. Studies
have shown that there is great variability in the
risk of SSIs even within the same incision
category.23,24 Also, this scheme does not take into
account any of the host or operation-related risk
factors, which makes it difficult to compare SSI
rates among hospitals or surgeons.
c) This SSI risk stratification scheme is no longer
used as the sole determinant of SSI risk.
2. In 1985, a new model was developed to stratify SSI
risk.23 This was based on a logistic regression of 10
variables collected in the Study of the Efficacy of
Nosocomial Infection Control (SENIC) project and
showed that four variables are independently
associated with SSI risk.
2
a) Abdominal operation.
b) Operation lasting more than 2 hours.
c) Surgical site with a wound classification of either
contaminated or dirty/infected.
d) Patient with three or more discharge diagnoses.
e) This model weighs these variables equally and
assigns a point value of one for each variable
present. Thus, the risk index values range from 0
(low risk) to 4 (high risk). This scheme was found
to be limited in that the number of discharge
diagnoses could not be determined until the time
of discharge; therefore, this did not allow for
prospective inpatient stratification..
3. The currently accepted method for SSI risk
stratification is the National Nosocomial Infections
Surveillance risk index. This index differs from those
described above in that it is operation specific and can
be applied to prospectively collected data. The risk
index weighs each of the following variables equally.
a) Surgical site wound classification of contaminated
or dirty/infected.
b) ASA score as rated by an anesthesiologist prior to
operation of 3 or greater.
c) Procedure time over T hours, where T is the 75th
percentile of the duration of surgery for the
specific procedure being performed.
d) A patient scores one point for each variable
present. Thus, the index can range from 0 to 3
with higher scores representing greater risk.
F. Surgical Site Infection Survellance Methods
The data obtained from SSI surveillance is useful to
many persons interested in decreasing the incidence
of SSIs at a particular institution. It can help to
determine the effectiveness of aseptic technique and
the efficacy of antimicrobial prophylaxis, and can aid
in the development and assessment of infection
control measures. Several studies have documented
the effectiveness of reporting surveillance data to
surgeons and other members of the surgical team with
a subsequent reduction in SSI rate of 34%-50%.25,26
Given the limits in resources, it is nearly impossible
for most institutions to monitor all surgical patients all
of the time. It is recommended that hospitals therefore
target surveillance toward high-risk procedures ideally
jointly chosen by infection control and surgeons.27
1. Inpatient SSI surveillance
a) Daily wound examination and chart review.
b) Selective chart review with Kardex review.
(1) The infection control practitioner searches
the Kardex for clues of infection, i.e. fever,
purulence reported by the nurse, antibiotic
use, etc. This method saves investigators time,
but is limited by the accuracy of the data in
the Kardex.
(2) Sensitivity 82%-94%28
c. Review of microbiology reports for positive
cultures from postsurgical patients.
(1) Sensitivity of only 33%-65%28,29
d) Review of pharmacy files for antibiotic use longer
than that allowed for prophylaxis.
(1) Low sensitivity
(2) Postdischarge SSI surveillance
This is an important area of interest because
studies have shown that up to 84% of SSIs
are detected after discharge.30,31 The CDC
previously recommended contacting
discharged patients 30 days after surgery to
determine whether an SSI had occurred, but
the revised 1999 guidelines call this practice
into question.31 One study has shown that
patients are not reliably able to assess their
own wounds for infection. At the present,
there is no standard method for performing
SSI surveillance outside the hospital. Below
are some methods that have been used to
perform outpatient SSI surveillance, but none
has been proven to be sufficiently effective to
recommend on its own.33
a) Direct examination of patient’s wounds
during follow-up visits.
b) Review of medical records of surgery
clinic patients.
c) Phone or mail questionnaires to patients.
d) Phone or mail questionnaires to surgeons.
G. Treatment of Surgical Site Infections34
1. Superficial wound infections
a) Cellulitis/erythema at wound margin and no
pus expressible.
(1) Usually caused by staphylococci and
streptococci and treated with an appropriate
antibiotic.
(2) Frequently is a sign of fluid collection in the
wound; consider aspirations of the wound.
2. Wound infection – pus or infected fluid leaks from
wound, failure to heal, or spontaneous dehiscence.
a) Wound should be reopened.
b) Consider surgical reexploration.
c) Debridement of necrotic tissue indicated.
d) Irrigation of wound using physiologic solutions
and packing with fine mesh sterile gauze.
3. Deep wound infections (infection of the fascia).
a) Signs: wound dehiscence, fever, elevated white
blood count, superficial wound infection,
organ/space infections with pus draining between
fascial sutures.
b) Treatment
(1) Remove fascial sutures.
(2) Ensure no fascial necrosis present.
(3) If fascial tension present and concern exists
regarding intestinal herniation, the fascial
defect may be allowed to persist and repaired
after infection resolved.
4. Antibiotic therapy is directed by Gram stain and
culture of purulent material and/or empirical
selection based on likely pathogens.
3
H. Microbiology of Surgical Site Infections
The patient’s endogenous flora is the primary reservoir
for organisms causing SSIs. However, the operating
room environment, hospital personnel, or seeding of
the operative site from a distant focus of infection also
play a role.
1. Skin
a) Gram-positive organisms: staphylococci and
streptococci primarily.
2. Gastrointestinal system
a) Mixed flora including enteric, gram-negative
bacilli, anaerobes, and gram-positive organisms
(including enterococci).
3. Genitourinary system
a) Gram-negative organisms primarily (Escherichia
coli, Klebsiella spp., and Pseudomonas) but also
some gram-positive organisms (enterococci).
4. Female genital tract
a) Enteric, gram-negative bacilli, enterococci,
group B streptococci, and anaerobes as well as
gram-positive organisms such as staphylococcus
and streptococcus..
5. Fungal infections as part of SSIs25
a) Factors that increase the risk of fungal infections
in surgical patients include the following:9
(1) Exposure to broad-spectrum antimicrobial
agents.
(2) Use of agents that decrease gastric acidity and
thereby promote growth of microorganisms
including yeast.
(3) Disruption of the gastrointestinal mucosal
barrier.
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