Causality evaluation of bacterial species isolated from patients with community‐acquired lower leg cellulitis

Abstract

Lower leg cellulitis is a diffuse inflammation of the cutaneous connective tissue following invasion of microorganisms and with potential to recur. The causative agent is not routinely identified in clinical practice, and the empirical therapy initiated primarily targets the 'conventional' disease pathogens, Streptococcus pyogenes and Staphylococcus aureus. To evaluate at case level, the role of bacterial species isolated from lesional skin in the pathogenesis of community-acquired lower leg cellulitis. Two sampling methods (superficial swab and biopsy) were applied to isolate bacterial species from 40 patients hospitalized for first (N = 24 cases) and recurrent (N = 16 patients) lower leg cellulitis episodes. Subsequently, a clinical-laboratory heuristic algorithm was employed to interpret causality associations of isolated species with disease episodes at case level. In 37/40 cases (92.5%), at least one bacterial species was identified with either sampling method. The number of different species/specimen isolated from superficial swabs compared to punch biopsies was significantly more (P < 0.001). A causative agent was identified in 16 cases (40%); it was a 'conventional' pathogen in seven patients and strains belonging to one of six 'non-conventional' pathogens in nine cases. There was no concordance in the spectrum of isolated pathogens with the two sampling methods (kappa-index = 0.028). Another four species may have participated in five patients as co-pathogens in mixed infections. There was also no difference in microbiological disease features between patients with first and recurrent cellulitis episodes. The application of a clinical-laboratory causality algorithm coupled with pooled culture results of more than one sampling methods in patients with lower leg cellulitis is anticipated to permit the identification of responsible bacterial species at case level and offer incentive for therapeutic intervention studies.