Dear Readers: In this installment of the Evidence Corner, we venture into the world of the infected wound. How do we know when a wound is infected? Is it a matter of “I’ll know it when I see it?” Do the symptoms of infection differ between acute and chronic wounds? Theoretical definitions of infection usually describe it as invasion of viable tissue by one or more types of microorganisms influenced by compromised host defenses, virulence of the organisms, and local tissue risk factors.[1] Yet practical measures of infection often fail to meet scientific standards of reliability and either diagnostic or predictive validity. The two articles below explore evidence addressing the reliability and validity of surgical and chronic wound infection measures with some surprising conclusions.

Quality of Surgical Wound Infection Measurements: A Systematic Review

Reference: Bruce J, Russell EM, Mollison J, Krukowski ZH. The quality of measurement of surgical wound infections as the basis for monitoring: A systematic review. J Hosp Infection 2001;49:99–108.

Rationale: Attempts to standardize the definition of surgical wound infection are challenging for both surgeons and infection control personnel.

Objective: Systematically assess the validity and reliability of definitions and methods of measuring surgical wound infection.

Methods: Authors searched the MEDLINE, CINAHL, EMBASE, Cochrane Library, and HealthSTAR databases from 1993 to 1999 for studies of inter-rater and intra-rater reliability, criterion, construct, and content or face validity of measures defining surgical wound infection. Studies were included in the analysis if a definition of surgical wound infection and/or details of wound assessment were described or if reliability and/or validity of the definition were assessed.

Results: Of 2,490 abstracts identified, 90 prospective studies from 20 countries qualified for inclusion in the analysis. These included 41 separate definitions of wound infection and eight articles formally assessing validity or reliability of the definition of surgical wound infection. Five “standard” definitions of wound infection were identified: 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. No single symptom was common to all definitions. The most common stand-alone criteria of infection were purulent discharge (54 studies, with positive bacterial culture mandatory in 12 of these 54 studies) and erythema or swelling (8 studies). Content, criterion, and construct validity studies of the different infection scales suggested that the ASEPSIS and Southampton Wound Assessment scales are more sensitive than the NPS and CDC definitions. Reliability of infection diagnoses ranged from 0.73 (physician inter-rater correlations with patient diagnosis of purulent discharge) to 0.96 (physician correlated with nurse diagnosis using ASEPSIS), with the “classic signs and symptoms” of infection (purulent discharge, tenderness, erythema, swelling, induration, warmth) yielding eight-percent false positives and 48-percent false negatives by patients as compared to nurses and doctors. The basic core symptoms in most studies included wound discharge (purulent or otherwise), redness or erythema, swelling or edema, pain, tenderness, heat, pyrexia, dehiscence, and separation of wound edges. Bacteria can be isolated from wounds that are healing without clinical signs of infection and conversely are often not isolated when cultured from early wound infections.

Conclusions: Surgical wound infection diagnosis is often subjective, based variably on the presence and severity of several properties, with no single objective gold standard test, not even isolating the organisms from tissue biopsies or wound fluid.