How Little We Know About Wound Bacterial Burden

Introduction: Wound colonization and infection are often asymptomatic and are therefore grossly under-detected in the chronic wound population. Typically polymicrobial in nature, the vast majority of wound pathogens emit red-fluorescing porphyrins or cyan-fluorescing pyoverdines that are detected by bacterial fluorescence imaging. Literature suggests the exceptions, Streptococcus and Enterococcus, exist monomicrobially in <1% of chronic wounds. Herein, we report the microbiological findings and fluorescence signals from 350 chronic wounds.

Methods: Wounds were selected on a first-com, first-served basis at 14 U.S. clinic sites by 20 clinicians and assessed first with IWII clinical signs and symptoms (CSS) checklist, followed by real-time fluorescence imaging. Images with regions of red or cyan were considered positive for moderate-to-heavy bacterial loads. Biopsies were taken and assessed via quantitative culture to confirm.

Results: Some 82% of study wounds were positive for bacterial loads ≥104 CFU/g, yet only 14% exhibited detectable CSS. Diagnostic odds ratio increased fourfold when fluorescence was incorporated. The positive predictive value of red or cyan fluorescence for detecting moderate-to-heavy bacterial loads (≥104 CFU/g) was 96%, and in 73% of cases the associated loads were 106 CFU/g or higher. Staphylococcus aureus was the most prevalent species detected (45% of biopsies). Known non-porphyrin-producing bacteria (Streptococcus and Enterococcus) were highly prevalent, but rarely occurred without accompanying porphyrin-producing (i.e., red-fluorescing) species. Only two study wounds (0.6%) with monomicrobial non-porphyrin producers at loads of >104 CFU/g went undetected by fluorescence.

Conclusion: Diagnosing high bacterial burden is paramount for appropriate wound treatment and optimal healing, but this multi-site study demonstrates that its prevalence is grossly underestimated in clinical practice. Fluorescence imaging represents a paradigm shift in wound assessment that will enhance wound-bacterial knowledge on a per patient level, as well as across the wound care field.