Diagnosis and treatment of the invasive extension of bacteria (cellulitis) from chronic wounds utilising point-of-care fluorescence imaging

Abstract

Early diagnosis of wound-related cellulitis is challenging as many classical signs and symptoms of infection (erythema, pain, tenderness, or fever) may be absent. In addition, other conditions (ie, chronic stasis dermatitis) may present with similar clinical findings. Point-of-care fluorescence imaging detects elevated bacterial burden in and around wounds with high sensitivity. This prospective observational study examined the impact of incorporating fluorescence imaging into standard care for diagnosis and management of wound-related cellulitis. Two hundred thirty-six patients visiting an outpatient wound care centre between January 2020 and April 2021 were included in this study. Patients underwent routine fluorescence scans for bacteria (range: 1-48 scans/patient). Wound-related cellulitis was diagnosed in 6.4% (15/236) of patients. In these patients, fluorescence scans showed an irregular pattern of red (bacterial) fluorescence extending beyond the wound bed and periwound that could not be removed through cleansing or debridement, indicating the invasive extension of bacteria (wound-related cellulitis). Point-of-care identification facilitated rapid initiation of treatments (source control and antibiotics, when warranted) that resolved the fluorescence. No patients had worsening of cellulitis requiring intravenous antibiotics and/or hospitalisation. These findings demonstrate the utility of point-of-care fluorescence imaging for efficient detection and proactive, targeted management of wound-related cellulitis.

Keywords: MolecuLight; cellulitis; fluorescence imaging; infection; wounds.

FIGURE 1

Decision tree for diagnosis of wound‐related cellulitis supported by fluorescence imaging. (A) Clinical decision tree incorporating fluorescence imaging information to identify wounds with bacteria burden, and potential cellulitis. (B) In wounds with surface colonisation, bacterial fluorescence signal is eliminated with aggressive wound hygiene strategies. (C) Red bacterial fluorescence in callused tissue is unlikely to be wound‐related cellulitis, but often appears pink or orange because of the subsurface location of bacteria below callus. (D) Bacterial fluorescence with irregular borders beyond the periwound region was indicative of wound‐related cellulitis in this patient. White arrows point to regions of red fluorescence indicative of bacteria at loads >10⁴ CFU/g. ‡Based on guidelines developed by Oropallo et al

FIGURE 2

Example 1, sacral pressure ulcer. Standard (left) and fluorescence (right) scans taken at initial assessment and at follow‐up 4 weeks later. (A, C) At initial assessment, fluorescence images showed bright red fluorescence (white or red arrows) indicative of elevated bacterial burden dispersed in macerated tissue and beyond periwound region. The wound underwent debridement and application of a topical antimicrobial. (B, D) At a follow‐up visit 3 weeks later, a significant reduction in red fluorescence in the periwound region was observed. The wound went on to heal 6 weeks after initial assessment

FIGURE 3

Example 2, suspected stasis dermatitis. (A, D) At initial presentation, a fluorescence scan of this recurrent venous leg ulcer showed a large region of bright red fluorescence in and around the wound bed (white arrows), indicative of elevated bacterial load. Scan and clinical information prompted initiation of antibiotics and topical antimicrobials. (B, E) At follow‐up several months later, the wound was treated with gentian violet (top, centre). Fluorescence scan showed an absence of red or cyan (bacterial) fluorescence in and around the wound. (C, F) Twelve months after initial diagnosis, wound‐related cellulitis was no longer observed and the wound had healed

FIGURE 4

Example 3, venous leg ulcer. (A, B) At initial examination, significant erythema was observed around wound. Fluorescence scan showed bright red fluorescence indicative of elevated bacterial burden (white arrows) in erythematous region surrounding the wound, supporting diagnosis of cellulitis. Antibiotics were initiated along with application of a topical antimicrobial. (C, D) After 6 weeks, the wound size and erythema were greatly reduced. Fluorescence scan also was negative for bacterial signal indicating the efficacy of selected treatments

FIGURE 5

Example 4, dorsal foot ulcer. (A) Upon initial examination, strong odour and erythema were detected from the wound and surrounding region. (B) Fluorescence scan showed red fluorescence beyond the periwound region (white arrows). The wound initially underwent debridement targeted to regions of red fluorescence, but red fluorescence signal persisted prompting the clinician to include antimicrobials and compression. (C, D) Three weeks after the diagnosis of wound‐related cellulitis, the wound size was significantly smaller and negative for bacterial fluorescence