A Cross-sectional Validation Study of Using NERDS and STONEES to Assess Bacterial Burden
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Abstract: All chronic wounds are colonized by micro-organisms. Although the presence of bacteria is not necessarily harmful, and may be beneficial in some instances, accurate evaluation of wound-related bacterial damage and infection is crucial. A cross-sectional validation study involving 112 patients was conducted to estimate the specificity and sensitivity of clinical assessment variables individually and in combination to determine the presence and quantity of bacteria in the wound. The average age of study participants was 66 years (range 33 to 95 years) and most had leg (44) and foot (68) ulcers of approximately 6 months’ duration. Wounds were evaluated using a mnemonic developed to evaluate the presence or absence of clinical signs of critical colonization (NERDS©) or infection (STONEES©) and results compared to semi-quantitative swab cultures. Wounds with debris, increased exudate, and friable tissue were found to be five times more likely to have scant or light bacterial growth; whereas, wounds with elevated temperature were eight times more likely to have moderate or heavy bacterial growth. When combining any three clinical signs, the sensitivity was 73.3% for scant or light and 90% for moderate and heavy bacterial growth and the specificity was 80.5% and 69.4%, respectively. Considering the importance of this clinical diagnosis, studies to examine the predictive validity of these assessment variables and culture results are warranted.
Key Words: wound infection, chronic wounds, assessment, bacterial swab
Potential Conflicts of Interest: Dr. Woo and/or Dr. Sibbald is a consultant, investigator, and/or speaker for one or more of the following companies/organizations: 3M (St. Paul, MN), Coloplast Corp. (Minneapolis, MN), Mölnlycke Health Care (Norcross, GA), Covidien (Mansfield, MA), Gaymar (Orchard Park, NY), KCI (San Antonio, TX), Systagenix Wound Management (Quincy, MA), Tyco International Ltd. (Mansfield, MA), ConvaTec (Skillman, NJ), Registered Nurses Association of Ontario (Canada), and the Government of Ontario.
Please address correspondence to: Kevin Y. Woo, RN, MSc, PhD, ACNP, GNC(C), FAPWCA, Wound Healing Clinic, East Room 1016, Women’s College Hospital, 76 Grenville Street, Toronto, Ontario M5S 1B2 Canada; email: email@example.com.
All chronic wounds are invariably colonized by a complex ecology of micro-organisms.1 More than 90% of chronic wounds have been found to host polymicrobial flora containing an average range of 1.6 to 4.4 bacterial species depending on the type of ulcer.2 The presence of nonreplicating micro-organisms on the wound surface that do not evoke clinical host response is referred to as contamination. As the micro-organisms continue to proliferate within the wound, critical colonization (ie, the presence of bacteria in the superficial wound compartment that are associated with a host inflammatory response that delays or prevents healing) and wound infection can occur, causing clinical host injury3 (see Table 1).
Although the presence of bacteria is not necessarily pathological and may actually facilitate normal healing,2 wound healing has been found to be noticeably compromised when the bacterial burden crosses a certain colonization threshold to overcome host resistance or incorporates more than four pathological bacterial species.4 Based on an analysis of wound fluid from their seminal case series, Bendy et al5 reported chronic pressure ulcer healing was significantly thwarted at a bacterial load of 1.0 x 106 or higher number of colony forming units per gram (CFU/g) of tissue.
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