Culturing Periprosthetic Joint Infection: Number of Samples, Growth Duration, and Organisms.

BACKGROUND: Owing to the difficulty isolating microorganisms in periprosthetic joint infection (PJI), current guidelines recommend that 3-5 intraoperative samples be cultured and maintained for 3-14 days. We investigated (1) the optimal number of culture samples and growth duration to diagnose PJI and (2) the microbiology profile at our institution.

METHODS: A retrospective review of 711 patients (329 hips, 382 knees) with PJI that met Musculoskeletal Infection Society criteria from 2000 to 2014 was performed. Two thousand two hundred ninety aerobic and anaerobic cultures were analyzed. A manual chart review collected demographic, surgical, and microbiological data. Microbiology profiles were trended. Logistic regression analysis was performed to determine statistical significance.

RESULTS: Obtaining 5 samples provided the greatest yield positive cultures for diagnosing PJI. The percentage of positive cultures overall was 62.6% and stratified by organism type: antibiotic resistant (80.0%), Staphylococcus aureus (76.0%), gram negative (58.9%), Pseudomonas (52.0%), variant PJI organisms (28.2%), Propionibacterium acnes (20.0%), and Escherichia coli (8.0%). Although most organisms were cultured in 5 days or less, 10.8 days were needed for Propionibacterium acnes, 6.6 for variant PJI organisms, and 5.2 for coagulase-negative Staphylococcus. At 3 days, only 42.2% of cultures turned positive compared with 95.0% at 8 days. There was a significant decrease in time in gram-positive PJIs and an increase in culture-negative PJIs.

CONCLUSION: The optimal number of cultures and growth duration depended on the type of organism. This study provides evidence that 5 samples should be obtained and held for at least 8 days given that the type of organisms is likely to be unknown at the time of surgery.