A Prospective Multisite Observational Study Incorporating Bacterial Fluorescence Information Into the UPPER/LOWER Wound Infection Checklists

Rosemary Hill, BSN, CWOCN, WOCC(C); Kevin Woo, PhD, RN, NSWOC, WOCC(C), FAPWCA

Disclosures

Wounds. 2020;32(11):299-308. 

In This Article

Abstract and Introduction

Abstract

Introduction: The UPPER/LOWER infection checklists look for signs and symptoms of local/superficial infection (UPPER) and deep infection (LOWER) to assist clinicians in identifying and distinguishing between these infection levels, facilitating appropriate treatment. The presence of 3 or more UPPER or LOWER criteria is indicative of infection.

Objective: This study evaluated the utility of incorporating real-time bacterial fluorescence imaging into the UPPER/LOWER checklists to enhance identification of infection in wounds.

Materials and Methods: This prospective, multisite study assessed 43 chronic wounds. Infection was identified in 27 wounds (62.8%) according to the UPPER/LOWER checklist criteria; 3 wounds were positive for both UPPER and LOWER infection, 1 wound was positive for LOWER infection only, and 23 wounds were positive for UPPER infection only. Fluorescence images were taken to detect wounds with high bacterial loads (> 104 CFU/g), indicated by the presence of red or cyan fluorescence.

Results: Red or cyan fluorescence from bacteria was observed in 88% of wounds (n = 38); all wounds positive for UPPER/LOWER were also positive for bacterial fluorescence. In 18 (41.9%) of the 43 wounds, fluorescence information added a third check to the UPPER/LOWER threshold, turning a negative diagnosis into a positive diagnosis of infection. Bacterial load was detected in 22/27 wounds swabbed, 17 of which exhibited heavy growth; in all wounds with detectable bacterial load, fluorescence signal was observed (positive predictive value = 100%, negative predictive value = 83%). Using microbiology as ground truth, inclusion of fluorescence information as an additional item in the checklists increased the sensitivity of the UPPER/LOWER checklist from 82% to 95% (P < .01).

Conclusions: These results suggest that the UPPER/LOWER checklist and fluorescence imaging work in a complementary manner to effectively identify wounds with high bacterial burden at the point-of-care.

Introduction

Wound care currently accounts for 5% of total health care spending and much of this cost stems from management of bacterial infection.[1] Timely diagnosis of high bacterial burden and infection in wounds is critical to wound healing outcomes and preventing the wound from escalating to local, spreading, or systemic infections. Indiscriminate and routine wound cultures are not recommended for the diagnosis of wound infection (superficial or deep).[2] Recognizing that all chronic wounds are colonized, a wound swab will always yield a positive culture that does not necessarily confirm or refute wound infection. Tissue biopsy is the gold standard to detect wound infection,[3] but it is not always feasible to obtain tissue samples (due to pain, bleeding, lack of expertise); hence, clinical evaluation is needed. Current best practices to diagnose wound infection involve inspection for clinical signs and symptoms, and, if necessary, collection of a wound sample for microbiological culture analysis.[4] Clinical signs and symptoms are a proxy for the presence of infection-causing bacteria and reflect a host response to elevated bacteria levels in the wound. Evaluation of signs and symptoms of infection may be subjective and variable,[5–7] but assessment of these signs and symptoms of infection is the most common method used to guide selection and evaluate efficacy of treatment. To enable easier recall and documentation, these numerous signs and symptoms of infection are often grouped together into mnemonics and checklists (eg, NERDS [nonhealing, exudate, red friable tissue, debris (discoloration), and smell] and STONEES [size increasing, temperature elevation, os (probes to bone), new breakdown, erythema/edema, exudate and smell], International Wound Infection Institute [IWII] Wound Infection checklist).[4,8,9] Mnemonics facilitate easy recall of information and greatly enhance the communication of wound status among members of the wound care team, but do not convey information on the presence and location of bacteria, thus limiting timely deployment of appropriate treatment.

Based on a review of the literature,[4,10] a set of wound infection checklists (UPPER and LOWER) were developed to describe 2 clusters of signs and symptoms associated with superficial/localized infection or deep tissue infection. There is no one individual sign or symptom that will accurately confirm the diagnosis of wound infection, but a combination of 2 or 3 of these possible signs is used to confirm diagnosis. Local infection involves unhealthy tissue, pain, poor healing, exudate, and reek (UPPER), while deeper infection includes a larger wound size, osseous tissue, warmth, edema, and redness (LOWER) (Figure 1). Using these mnemonics to distinguish between local and deeper infection at the time of evaluation provides valuable information to guide treatment decisions. For example, presence of 3 or more signs and symptoms from the UPPER checklist indicates the presence of a local infection, which may prompt the clinician to eliminate from consideration the need for antibiotics, whereas presence of 3 or more symptoms from the LOWER checklist including a larger wound size, presence of osseous tissue and edema indicates a deeper, systemic infection that may prompt the clinician to sample the wound to determine load and species of bacteria as well as commence application of antibiotics.

Figure 1.

UPPER and LOWER checklists with bacterial fluorescence imaging as an additional sign. The presence of 3 or more UPPER checklist items indicates a local infection, while the presence of 3 or more LOWER checklist items indicates a deeper infection. Fluorescence imaging is used to detect bacteria at loads >104 CFU/g.

Reliance on signs and symptoms of infection alone to infer whether critical levels of bacteria are present in the wound remains challenging due to the subjectivity of clinician evaluation and variability or absence of host response to bacterial infection.[11,12] For instance, patients who are immunocompromised may only present with a wound that is not healing or is worsening when an infection is present, as other signs and symptoms may be suppressed.[13] Further, these criteria do not provide information on the location of bacteria, which is necessary to determine the location and extent of wound bed preparation. The inclusion of fluorescence imaging to detect bacteria during routine wound assessment may help to overcome these limitations when diagnosing for infection.

Fluorescence imaging (FL) entails the use of a handheld, non-contact imaging device (MolecuLight i:X; MolecuLight Inc) to detect fluorescence from bacteria and wound tissues at the bedside. This imaging device emits a safe violet light (405 nm) that excites tissue and bacteria. Most bacteria emit red fluorescence due to endogenous production of red fluorescent porphyrins,[14] while Pseudomonas aeruginosa uniquely produces cyan fluorescence due to production of pyoverdine.[15] Under violet light, red fluorescence is observed from most common wound pathogens (Gram positive and Gram negative, aerobes and anaerobes) including pathogens found in biofilm; however, it cannot distinguish between biofilm and planktonic bacteria.[16] Multiple clinical studies have demonstrated that the presence of red or cyan fluorescence in wounds is indicative of moderate-to-heavy bacterial loads (> 104 CFU/g), with positive predictive values (PPV) greater than 95%.[8,17,18] The images produced from this procedure provide objective diagnostic information on bacterial presence to improve assessment and treatment selection.[8] In this multisite, prospective observational study, the authors evaluated the utility of integrating point-of-care bacterial FL into standard of care assessment using the UPPER/LOWER wound infection checklists and the effects of FL on the communication of wound status among the wound care team.

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