Evaluation of Sonicate Fluid Culture Cutoff Points for Periprosthetic Joint Infection Diagnosis.

Introduction: Implant sonication is useful for recovery of periprosthetic joint infection (PJI) pathogens in culture, but exact cutoff points for definition of clinically significant sonicate fluid culture results vary from study to study. The aim of this study was to define ideal sonicate fluid culture cutoff points for PJI diagnosis.
Methods: Sonicate fluid cultures from hip and knee prosthesis components removed between February 2007 and December 2020 were studied. Prosthesis components were placed in solid containers in the operating room; in the clinical microbiology laboratory, 400 mL Ringer's solution was added, and containers subjected to vortexing, sonication and then vortexing, followed by centrifugation. Concentrated sonicate fluid was plated on aerobic and anaerobic solid media, and culture results reported semiquantitatively, as no growth, <20, 20-50, 51-100, or >100 CFU/10 mL sonicate fluid. Sonicate cultures from cement spacers and cultures yielding more than 1 microorganism were excluded. Sensitivity and specificity of each cutoff point was evaluated.
Results: A total of 1448 sonicate fluid cultures were evaluated, 68% from knees and 32% from hips. PJI was present in 644 (44%) cases. Sensitivity of sonicate culture was 75.0% at <20 CFU/10 mL, 55.3% at ≥20 CFU/10 mL, 46.9% at >51 CFU/10 mL, and 39.8% at >100 CFU/10 mL. Specificity was 78.2%, 99.8%, 100%, and 100%, at the 4 cutoff points, respectively.
Conclusions: A cutoff point for sonicate fluid culture positivity of ≥20 CFU/10 mL is suitable for PJI diagnosis.
Competing Interests: Potential conflicts of interest. M.P.A. has royalties with Striker, OsteoRemedies, and Springer and is in the board of directors of AAHKS, IOEN, and Mid-America. R.P. reports grants from ContraFect, TenNor Therapeutics Limited, and BIOFIRE; is a consultant to PhAST, Day Zero Diagnostics, Abbott Laboratories, and CARB-X; has research supported by Adaptive Phage Therapeutics (APT); Mayo Clinic has a royalty-bearing know-how agreement and equity in APT; has a patent on Bordetella pertussis/parapertussis PCR issued, a patent on a device/method for sonication with royalties paid by Samsung to Mayo Clinic, and a patent on an anti-biofilm substance issued; and receives honoraria from Up-to-Date and the Infectious Diseases Board Review Course. All other authors report no potential conflicts.
(© The Author(s) 2024. Published by Oxford University Press on behalf of Infectious Diseases Society of America.)