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NUMBER 3-4 YEAR 2009
Accuracy of Surgical Wound Infection Definitions - The First Step Towards Surveillance of Surgical Site Infections
1 Emergency Department,
2 Department of Anesthesiology and Intensive Care,
3 Bega Clinic of Obstetrics and Gynecology, Clinical Emergency County Hospital, Timisoara,
4 Division of Microsurgery, Pius Branzeu Center for Laparoscopic Surgery and Microsurgery, Victor Babes University of Medicine and Pharmacy, Timisoara

Correspondence to:
Alina Petrica, Emergency Department, County Emergency Hospital Timisoara, 10 I. Bulbuca Blvd., Timisoara, Romania,
Tel. +40-747-025027.
Infectiile postoperatorii reprezinta o complicatte frecvent intalnita, ce se asociaza cu morbiditate si mortalitate crescuta si totodata costuri ridicate pentru sistemul sanitar. Iin multe centre din intreaga lume exista o preocupare constanta pentru monitorizarea infectiilor postoperatorii in vederea stabilirii dimensiunii acestei probleme si a metodelor de prevenire a acesteia. Articolul de fata isi propune sa evalueze validitatea si acuratetea definitiilor utilizate pentru infectiile postoperatorii. Utilizarea unor definitii standardizate este fundamentala pentru obtinerea unor rezultate cat mai exacte in urma monitorizarii infectiilor de plaga postoperatorie.

Surgical site infections (SSIs) are a common postoperative complication and represent a significant burden in terms of patient morbidity and mortality, and cost to health services around the world.1 The surveillance of SSIs has been undertaken in many centres worldwide to ascertain the extent of the problem and where possible, to improve the incidence rates, thereby decreasing the undesirable outcomes.2 This paper aims to assess the validity and reliability of definitions and methods of measuring surgical wound infection. The use of standardized definitions is fundamental to the accurate measurement and monitoring of SSIs.

Surveillance is defined as "the ongoing, systematic collection, analysis, and interpretation of health data essential to the planning, implementation, and evaluation of public health practice, closely integrated with the timely dissemination of these data to those who need to know".1-3 Surveillance identifies clusters of infection, risk factors and establishes risk indexes for infection, provides comparisons between hospitals or surgical specialties, and permits evaluation of control measures.4
An ideal surveillance system should have several attributes: meaningful definitions of infection, consistent interpretation of classification criteria, applicability to procedures performed in both inpatient and ambulatory facilities, ability to detect events after discharge, sufficient precision to distinguish small absolute differences in attack rates, and reasonable cost.5-7
In 2001, Bruce et al made a comprehensive review of the literature in searching for evidence for the validity and reliability of definitions of wound infection.8 Authors searched the MEDLINE, CINAHL, EMBASE, Cochrane Library, and HealthSTAR databases from 1993 to 1999 and strict inclusion and exclusion criteria were applied to studies retrieved for appraisal. Of 2,490 abstracts identified to assess the definition of surgical wound infection, 90 prospective studies from 20 countries were included in the analysis. Forty-one different definitions of surgical wound or SSI were identified; some were “standard” definitions used by national surveillance programmes: the Public Health Laboratory Service (NPS), the Surgical Infection Society Study Group, the Second UK National Prevalence Survey, and the Centers for Disease Control (CDC) 1988 and 1992 definitions. There was no single symptom common to all definitions, but the most common criteria of infection was purulent discharge.


The most widely recognized definition of infection, used throughout the USA and Europe, is that devised by Horan and colleagues and adopted by the CDC.9 According to CDC definition, surgical site infections are classified into three groups – superficial, deep incisional SSIs and organ-space SSIs – depending on the site and the extent of infection. These definitions are summarized in Table 1.
ASEPSIS is an acronym of seven wound assessment parameters. (Table 2)
Table 1. CDC definitions of surgical site infections.
Table 2. ASEPSIS wound scoring system.
It’s a quantitative scoring method that provides a numerical score related to the severity of wound infection using objective criteria based on wound appearance and the clinical consequences of the infection.10,11
The ASEPSIS system was ment to assess wounds resulting from cardiothoracic surgery, while the Southampton scale was designed for use in the postoperative assessment of hernia wounds.
The Southampton system is much simpler than the ASEPSIS system, with wounds being categorized according to any complications and their extent.12 Both systems, however, have been developed for use following specific types of surgery and this may limit their usefulness.1
Southampton scale - by using the worst wound score recorded and information about any treatment instituted either in hospital or the community, wounds were regarded in four categories: (Table 3)
a. normal healing;
b. minor complication;
c. wound infection - wounds graded IV or V, or wounds treated with antibiotics after discharge from hospital, irrespective of the wound grading given to them by the nurse;
d. major haematoma-wound or scrotal haematomas requiring aspiration or evacuation.
Table 3. Southampton wound scoring system.


Wilson et al. in his study from 1998, compared two standard definitions [Centers for Disease Control (CDC), USA and National Prevalence Survey (NPS), UK] with ASEPSIS and Southampton scales examining 325 wounds in 230 patients (divided into two groups).13 There was no significant difference between the two surveys. The two scoring methods were more sensitive than the standard definitions but CDC and NPS did not differ significantly from each other. For ASEPSIS it was reported an interrater reliability of 0.96 in patients having general surgery and similar reliability for sternal and leg wounds of patients after cardiac surgery.
In 2004 Wilson and Bruce made a study on 4773 patients in order to assess the level of agreement between definitions.
The mean percentage of wounds classified as infected differed substantially between definitions: 19.2% with the CDC definition (95% confidence interval 18.1% to 20.4%), 14.6% (13.6% to15.6%) with the NINSS version, 12.3% (11.4% to 13.2%) with pus alone, and 6.8% (6.1% to 7.5%) with an ASEPSIS score > 2014.
The agreement between definitions with respect to individual wounds was poor. When superficial infections (according to CDC category) were included, 13% (778) of all observed wounds received conflicting diagnoses, and 6% were classified as infected by both definitions. When superficial infections were excluded, the two definitions estimated about the same overall percentage of infection (6.8% and 7.0% respectively), but there were almost twice as many conflicting infection diagnoses (n = 371) as concordant ones (n = 215). Surgical wounds where pus was present were diagnosed as infected by the CDC, NINSS, and pus alone definitions, but only 39% of these (283/714) had ASEPSIS scores > 20. In these cases, greater infection severity was often diagnosed by CDC scale comparing with ASEPSIS. In wounds without pus the relation of ASEPSIS and CDC scales was less consistent. 42% (177/421) of wounds classified only as “disturbance of healing” by ASEPSIS were considered infected by the CDC definition. Conversely, four of the six wounds classified as “severe wound infections” by ASEPSIS were classified as superficial by the CDC definition. Finally, classifications with different definitions disagreed for more than twice as many wounds as those for which they agreed, and small changes in the interpretation of a definition caused substantial variation in the percentage of wounds classified as infected.
Also in 2004, Chiew YF and Theis JC studied infection rate of total hip replacement operations using different methods of assessment of surgical site infections. These were: (a) clinician diagnosis; (b) ASEPSIS score; (c) presence of pus cells; and (d) assessment by a clinical microbiologist. Two hundred and six patients were enlisted in the study and 189 primary replacements and 22 revision replacements were carried out. Infection rates which were calculated according to the risk indexes varied considerably among these four methods. The infection rates for risk index 0 were 4.35% (method a), 2.61% (method b), 0.87% (methods c and d); and for risk indexes 1 and 2 were 4.17% (method a), 2.08% (method b), 1.04% (methods c and d). The CDC NNIS approach places an important role on the surgeon who may be more inclined to prescribe antimicrobials for suspected infections, that being the reason for higher rates of SSIs when the CDC definitions are used.


There is no validated universal system designed specifically to aid the assessment and management of surgical wounds. The most commonly used, the CDC definition, employs stringent criteria to classify infection. A single, standard definition of surgical wound infection is needed so that comparisons over time and between departments and institutions are valid, accurate and useful. Meanwhile, comparisons will be compromised by discrepancies in the way that infections are defined. So, using wound infection rates as a performance indicator to compare centres or countries is probably premature.

1. Gottrup F, Melling A, Hollander A. An overview of surgical site infections: aetiology, incidence and risk factors, EWMA Journal 2005;5(2):11-5.
2. Chiew Y-F, Theis J-C, Comparison of infection rate using different methods of assessment for surveillance of total hip replacement surgical site infections, ANZ J. Surg. 2007;77:535-9.
3. Ehrenkranz NJ. Surgical wound infection occurrence in clean operations. Am J Med 1981;70:909-14.
4. Gaynes RP, Horan TC. Surveillance of nosocomial infections. In: C.G. Mayhall, editor. Hospital epidemiology and infection control. 2nd Ed. Baltimore: Lippincott, Williams and Wilkins, 1999.
5. Mangram AJ, Horan TC, Pearson ML, et al. Guideline for the prevention of surgical site infection. Infect Control Hosp Epidemiol 1999;20:247-78.
6. Manian FA, Meyer L. Comprehensive surveillance of surgical wound infections in outpatient and inpatient surgery. Infect Control Hosp Epidemiol 1990;11:515-20.
7. Platt R, Yokoe D, Sands K. Automated Methods for Surveillance of Surgical Site Infections, Emerg Infect Dis. 2001;7(2):212-6.
8. Bruce J, Russell EM, Mollison J, et al. The quality of measurement of surgical wound infections as the basis for monitoring: A systematic review. J Hosp Infection 2001;49:99-108.
9. Horan TC, Gaynes RP, Martone WJ. CDC definitions of nosocomial surgical site infections, 1992: a modification of CDC definitions of surgical wound infections. Infect Control Hosp Epidemiol 1992;13(10):606-8.
10. Bruce J, Russell EM, Mollison J. The measurement and monitoring of surgical adverse events. Health Technol Assess 2001;5(22):1-194.
11. Wilson AP, Treasure T, Sturridge MF. A scoring method (ASEPSIS) for postoperative wound infections for use in clinical trials of antibiotic prophylaxis. Lancet 1986; i:311-3.
12. Bailey IS, Karran SE, Toyn K. Community surveillance of complications after hernia surgery. BMJ 1992;304(6825):469-71.
13. Wilson AP, Helder N, Theminimulle SK. Comparison of wound scoring methods for use in audit. J Hosp Infect. 1998;39(2):119-26.
14. Wilson APR, Gibbons C, Bruce J. Surgical wound infection as a performance indicator: agreement of common definitions of wound infection in 4773 patients BMJ 2004;329:720-3.

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