# Limited Diagnostic Value of Blood Cultures in Patients with Soft Tissue Infections Transferred to a Quaternary Care Center

## TL;DR

Blood cultures taken after patients with soft tissue infections are transferred to a high-level care center rarely provide useful diagnostic information.

## Contribution

The study shows that blood cultures after transfer to a quaternary care center have limited diagnostic value in soft tissue infections.

## Key findings

- Only 5% of blood cultures taken after transfer were positive.
- Most positive post-transfer cultures were not clinically significant pathogens.
- Perineal necrotizing infections had very low post-transfer blood culture positivity.

## Abstract

Introduction: Patients with soft tissue infection are often encountered in clinical practice. The mainstay of treatment typically includes antimicrobial therapy, followed by surgical debridement when indicated. Blood cultures are often performed prior to starting the first dose of antibiotics. However, when patients require transfer to tertiary/quaternary-level care for more advanced surgical interventions, blood cultures are often repeated despite patients being on broad-spectrum antibiotics. Our study aims to investigate the utility of blood cultures following transfer to a higher level of care. Methods: This is a retrospective study involving adult patients (≥18 years of age) who were transferred to a quaternary academic center with soft tissue infections between 15 June 2018 and 15 February 2022. Patients with incomplete medical records and/or without blood culture data after arrival were excluded. The primary outcome was the rate of positive blood cultures post-transfer. Descriptive analyses were performed, and comparisons between groups were expressed as absolute differences and 95% CI. Results: We analyzed 303 patients with a mean (+/−SD) age of 54 (14) years, and 199 (66%) were male. Necrotizing soft tissue infections (NSTIs) predominated, 198 patients (65%), with a majority of the NSTIs involving the perineum (112, 37%). The prevalence of positive blood cultures was 20 (7%) for pre-transfer and 14 (5%) for post-transfer. Among post-transfer positive blood cultures, 3 (21%) were coagulase-negative Staphylococcus aureus, with 2 (14%) cases each for the blood culture categories of polymicrobial, methicillin-sensitive Staphylococcus aureus, and Enterococcus faecalis, and 2 (14%) with Candida species. Among 112 patients with NSTIs of the perineum, 2 (14%) patients had positive blood cultures post-transfer, compared with 110 (38%) patients with negative blood cultures (difference 24%, 95% CI −0.40, −0.12, p < 0.001). Conclusions: For patients with soft tissue infection, the prevalence of positive blood culture after arrival at our quaternary care center was low at 5%. Pathogenic cases of positive blood cultures after transfer were polymicrobial, methicillin-sensitive Staphylococcus aureus and Candida species. However, the low number of post-transfer positive blood cultures limits the strength of the inference and should be interpreted cautiously. Further studies are necessary to confirm our observation. Clinicians at tertiary/quaternary care centers should consider the utility of obtaining blood cultures from patients with soft tissue infections transferred from other facilities.