Surgical Science, 2011, 2, 73-76
doi:10.4236/ss.2011.22016 Published Online April 2011 (http://www.SciRP.org/journal/ss)
Copyright © 2011 SciRes. SS
External Validation of SENIC and NNIS Scores for
Predictıng Wound Infection in Colorectal Surgery
Tezcan Akin1, Merve Akin1, Serdar Topaloğlu2, Hüseyin Berkem3, Bülent Yüksel3,
Süleyman Hengirmen3, Yiğit Yildiz4, Mesut Tez5
1Department of Surgery, Kırıkkale Yüksek İhtisas Hospital, Kırıkkale Turkey
2Department of Surgery, Farabi Hospital, Karadeniz Thecnical University School of Medicine, Trabzon, Turkey
3First Department of Surgery, Ankara Numune Training and Research Hospital, Ankara, Turkey
4Department of Surgery, Derince Training and Research Hospital, Kocaeli, Turkey
5Fifth Department of Surgery, Ankara Numune Training and Research Hospital, Ankara, Turkey
Received September 3, 2010; revised February 25, 2011; accepted March 1, 2011
Objective: We aimed to identify the ratio of Surgical Site Infection (SSI) and also the validity of the National
Nosocomial Infection Surveillance (NNIS) and Study on the Efficacy of Nosocomial Infection Control
(SENIC) risk indexes in colorectal surgery, among Turkish population. Background: Some problems have
been reported with the power of NNIS risk index to predict the risk of surgical site infection. We aimed to
validate theNNIS and SENIC risk indexes in colorectal surgery. Methods: Between January 2003 and De-
cember 2006, surgical site ınfection surveillance was performed to 107 patients who undergo colorectal sur-
gery with NNIS and SENIC risk scales. The mean patient age was 48 years (range, 17 to 86), and 61.7% of
the group (66) was female. For this patient cohort, 6 (5.6%) were diagnosed with incisional SSI. While the
mean Body Mass Index (BMI) of all patients was 26.6; mean value of BMI among the patiens with SSI was
27.8.Results: 6 insicional surgical site infection were observed during the study. According to Receiver Op-
erating Characteric (ROC) curve analyze neither NNIS with avalue of 0.70, nor SENIC with a value of 0.67
are perfect risk indexes. Conclusion: As a result both NNIS and SENIC ıs a good risk indexes but not perfect.
Scarcely when NNIS and SENIC is used together to predict the SSI they forecast the development of infec-
tion better. But there is a lot of other factors that effect the development of SSI, so for excellent surveillance
risk index those factors known by everyone must be added to risk index scales.
Keywords: National Nosocomial Infection Surveillance (NNIS), Study on the Efficacy of Nosocomial
Infection Control (SENIC), Colorectal Surgery, Validation
Surgical site infection (SSI) is the most frequently re-
ported infection among surgical patients, acconting for
14% to 16% of all nosocomial infections among hospi-
talized patients. (10) These infections are associated with
significant morbidity and considerably extend the length
of hospital stay.
Surveillance has been described as a prevantive meas-
ure for reducing such infections. (3) A succesfull sur-
veillance system that uses standart definitions, which
feedsback data on-site-specific, risk-adjusted SSI rates
may provide a measure of quality performance for sur-
geons and hospitals and contribute to the prevention of
hospital acquired infections. (11)
For many years wound contamination class was the
only factor that was well described for predicting the risk
for SSI. During the Study on the Efficacy of Nosocomial
Infection Control (SENIC) Project, an index was devel-
oped that provided a better assesment of the risk of SSI
than had the traditional wound classification system. In
1991, a modification of the SENIC risk index by Culver
et al. led to the National Nosocomial Infections
Surveillance (NNIS) System risk index. (3)
SSI in patients undergoing colorectal resection have
been specifically studied, with similar general findings.
74 M. AKIN ET AL.
However, there has been wide discrepancy in the re-
ported incidence of incisional SSI following colorectal
surgery, ranging from 3 to 30%. Additionally, there has
been no clear consensus on the risk factors contributing
to SSI following colorectal surgery, which has limited
the data’s value to surgeons involved in quality im-
provement programs hoping to address specific variables
that could reduce this risk.(12)
Several authors have recognized that risk adjustment
needs to be improved and tailored to be procedure spe-
cific. Other’s have presented results of studies to identify
procedure specific risk factors for SSI for example, in
cesaerean sections and colorectal surgery. Therefore in
this study we aimed to identify the ratio of SSI and also
the validity of the NNIS and SENIC risk indexes in co-
lorectal surgery, among Turkish population.
Betwen January 1, 2003 and December 31, 2006, we
collected and analyzed data prospectively from patients
who underwent colorectal operations. Patients were fol-
lowed up from admission to 30 days after the date of
surgery. Patients who were discharged before the 7th day
after surgery were contacted by telephone at home.
SSI was diagnosed using the ASEPSIS score and
scores more than 20 points indicated infection where as
20 or less points were determined as disturbance of
healing. The definition for the acronym ASEPSIS is A,
additional treatment; S, serous discharge; E, erythema; P,
purulent exudate; S, separation of deep tissue; I, isolation
of bacteria; and S, stay as inpatient for >14 days. (15)
The components of the NNIS (4) surgical patient risk
index used in this study were as fallows: 1) Preoperative
American Society of Anesthesiologists (ASA) score; 2)
The traditional surgical wound classification; 3) T time
“defined as the 75 th percentile of the duration for op-
erative procedure and the components of the SENIC(7)
surgical patient risk index used in this study were as fal-
lows: 1) The traditional surgical wound classification; 2)
number of coexisting diagnoses; 3) Site of surgery; 4)
duration of surgery over 2 hours.
2.1. Statistical Analysis
Scoring system validation comprised two activities. These
are discrimination and calibration. Model discrimination
was measured by the area under the receiver–operator
characteristic (aROC) curve. Calibration was assessed
using the Hosmer–Lemeshow goodness-of-fit test and the
corresponding calibration curves. (1) All statistical analy-
sis in this study was performed using SPSS software
(version 11.0, SPSS Inc., Chicago, IL). (12)
During the 4-year period, 107 patients were identified
who underwent elective colorectal resection performed.
Demographic and clinical characteristics of the study
patients are shown in Table 1. The mean patient age was
48 years (range, 17 to 86), and 61.7% of the group (66)
was female. For this patient cohort, 6 (5.6%) were diag-
nosed with incisional SSI. While the mean Body Mass
Index (BMI) of all patients was 26.6; mean value of BMI
among the patiens with SSI was 27.8.
The aROC of NNIS was 0.70, compered with the
SENIC score which had an aROC of 0.67 (Figure 1). İf
aROC is 1this means that the procedure analyzed is per-
fect so the SENIC and NNIS are good but not perfect.
After the ROC curve analyze calibration of models were
assesed. The overall percentage for NNIS was 68.8, and
the overall percentage of SENIC was 61.5 (Table 2).
Where NNIS shows the infection 68.8%of patients and
SENIC shows 61.5%.
Surveillance systems aim to provide to feedback to hos-
pitals and stimulate infection control activities. An ade-
quate method for risk adjustment is important for the
comperison of hospitals’ specific rates. (3) Researchers
in a number of countries have found that the NNIS risk
index performed favorably for prediction of SSI. (9,2)
Not all experts concede that the NNIS risk index is the
best method for the risk stratification of all surgical pro-
cedures. For example, several studies have shown that
the NNIS risk index does not necessarily work well for
patient undergoing cardiothorasic procedures; as a result,
the authers of these studies have proposed modifications
that improve risk scoring systems. (5)
Data from the NNIS system suggest that approimately
%50 of all SSIs diagnosed in the United States are super-
ficial insicional SSIs. (7) Therefore only insicioinal SSIs
are included to the recent study.
Our rate of incisional SSI for elective colorectal resec-
tions (5.6%) is lower than predicted by general review of
the literature. Although there is a wide range of frequen-
cies reported, from 3% to 30%, the average rates for
wound infections reported is roughly 10%. There are a
number of potential explanations for these discrepancies.
(6,13) First, the emergent patiens were excluded from the
study, only electicve colon and rectum resections were
evaluated. Second, mechanical bowel preparation were
performed to all patients the day before the operation.
Although Topaloğlu et al. (14) were found that the
corelation of SENIC score with postoperative wound
ınfection is higher than NNIS, according to discrimination
Copyright © 2011 SciRes. SS
M. AKIN ET AL.
Copyright © 2011 SciRes. SS
Table 1. Demographic and clinical characteristics of patients.
Characteristics Number (%) Characteristics Number (%) Characteristics Number (%)
Gender NNIS Infection (-) 101(94.4)
Male 41(38.3) 0 71(66.4) Infection (+) 6(5.6)
Female 66(61.7) 1 32(29.9)
BMI ASEPSIS Age 20-95(av.58.4)
<25 25(23.3) 1(0-10) 88(82.2)
25-30 65(60.7) 2(11-20) 13(12.1)
30> 17(15.8) 3(21-30) 5(4.7)
ASA SENIC Symptoms Stomachace
1 16(15) 0 58(54.2) Constipation
2 55(51.4) 1 42(39.3)
3 35(32.7) 2 5(4.7)
4 1(0.9) 3 2(1.9)
BMI: Body Mass Index; ASA: American Society of Anesthesiologists; NNIS: National Nosocomial Infection Survellance; ASEP-
SİS: A, additional treatment; S, serous discharge; E, erythema; P, purulent exudate; S, separation of deep tissue; I, isolation of bac-
teria; and S, stay as inpatient for >14 days.; SENIC: Study on the Efficacy of Nosocomial Infection Control.
Table 2. Performance summary of the NNIS and SENIC
systems according to Hosmer-Lemeshow goodness-of-fit test.
analysis with aROC curve, in recent study, neither NNIS
nor SENIC are perfect risk indexes. But when compere
them with each other NNIS is more reliable than SENİC
(0.67) with aROC value of 0.70.
Infection (+) Infection (-) Overall percentage
NNIS 86.2 49 68.8%
SENIC 46.6 78.4 61.5%
As a result both NNIS and SENIC ıs a good risk in-
dexes but not perfect. Scarcely when NNIS and SENIC
is used together to predict the SSI they forecast the de-
velopment of infection better. But there is a lot of other
factors that effect the development of SSI, so for excel-
lent surveillance risk index those factors known by eve-
ryone must be added to risk index scales.
NNIS: National Nosocomial Infection Survellance; SENIC: Study on the
Efficacy of Nosocomial Infection Control; Infection (+): Observed Surgical
Site İnfection; Infection (-): no surgical site infection observed.
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