Slovenská chirurgia 1e/2026

Impact of specimen type and pre-analytical conditions on culture results in skin and soft tissue infections (SSTIs)

Objective: The aim of the study was to evaluate the impact of sample type and pre-analytical processing conditions on culture examination results in patients with skin and soft tissue infections.

Material and methods: This was a prospective comparative observational study conducted between January 2022 and March 2024. The present work represents a subanalysis of a broader prospective study focused on patients with skin and soft tissue infections. The cohort consisted of 90 surgical procedures in 66 patients, with the sampling series defined as the basic analytical unit. In total, 90 sampling series and 597 samples processed using different sampling and pre-analytical handling modalities were analysed. Agreement between modalities was assessed using Gwet’s AC1 coefficient and the Brennan-Prediger coefficient. Factors influencing the probability of a positive culture result were analysed using a generalized linear mixed model (GLMM).

Results: A positive culture result was found in 58.1 % (347/597) of all examined samples. Descriptive analysis showed no statistically significant differences among the 11 compared modalities (Pearson’s χ² = 14.890; p = 0.136). The mean number of microorganisms per sample, used as a descriptive yield index, was 0.66 ± 0.63, and no significant differences between modalities were confirmed even in the exploratory comparison using the Kruskal-Wallis test (H = 15.011; p = 0.132). A total of 396 microbial isolates were recovered from 347 positive samples, with the seven most frequent pathogen groups accounting for 82.1 % of all isolates. Gwet’s AC1 reached 0.600 for binary positive/negative assessment and 0.687 for microbial profile assessment. In the analysis of the whole cohort, primary operative revision (OR 6.19; p = 0.003) and sample type as a whole (p < 0.001) were significant predictors of a positive culture result, with swabs showing a higher probability of positivity than tissue samples (OR 2.74; p < 0.001). Duration of storage, storage conditions, and processing system were not confirmed as independent predictors, while the effect of antibiotic treatment before sampling remained borderline (OR 0.22; p = 0.054). After restricting the analysis to the most frequent and mutually comparable modalities, the effect of primary operative revision (OR 5.21; p = 0.007), antibiotic treatment before sampling (OR 0.17; p = 0.030), and sample type (swab vs. tissue: OR 2.88; p < 0.001) remained significant, whereas storage duration and storage conditions did not.

Conclusion: In this cohort of patients with skin and soft tissue infections, the probability of a positive culture result was associated mainly with sample type and the clinical context of the procedure, represented by primary operative revision. After restricting the analysis to the most frequent and mutually comparable modalities, antibiotic treatment before sampling was also associated with a lower probability of culture yield. In contrast, neither storage duration nor storage conditions were confirmed as independent predictors.

Keywords: skin and soft tissue infections, culture examination, swab, tissue sample, pre-analytical conditions