# Time to Positivity in Blood Culture Bottles Inoculated with Sonication Fluid from Fracture-Related Infections

## TL;DR

This study examines how quickly bacteria grow in blood culture bottles from fracture-related infections, helping guide antibiotic treatment decisions.

## Contribution

The study provides new data on time to positivity for sonication fluid cultures in fracture-related infections.

## Key findings

- Streptococcus species had the fastest time to positivity (median 11.9 hours).
- All Gram-negative bacteria were detected within 24 hours of inoculation.
- Staphylococcus aureus was the most prevalent organism in the samples.

## Abstract

The timely and accurate identification of causative agents is crucial for effectively managing fracture-related infections (FRIs). Among various diagnostic methods, the “time to positivity” (TTP) of cultures has emerged as a valuable predictive factor in infectious diseases. While sonication of implants and inoculation of blood culture bottles with sonication fluid have enhanced sensitivity, data on the TTP of this microbiological technique remain limited. Therefore, patients with ICM criteria for confirmed FRI treated at our institution between March 2019 and March 2023 were retrospectively identified and their microbiological records were analyzed. The primary outcome parameter was TTP for different microorganism species cultured in a liquid culture collected from patients with confirmed FRI. A total of 155 sonication fluid samples from 126 patients (average age 57.0 ± 17.4 years, 68.3% males) was analyzed. Positive bacterial detection was observed in 78.7% (122/155) of the liquid culture pairs infused with sonication fluid. Staphylococcus aureus was the most prevalent organism (42.6%). Streptococcus species exhibited the fastest TTP (median 11.9 h), followed by Staphylococcus aureus (median 12.1 h) and Gram-negative bacteria (median 12.5 h), all of which had a 100% detection rate within 48 h after inoculation. Since all Gram-negative pathogens yielded positive culture results within 24 h, it could be discussed if empirical antibiotic therapy could be de-escalated early and limited towards the Gram-positive germ spectrum if no Gram-negative pathogens are detected up to this time point in the context of antibiotic stewardship.