Assessing yield and impact of 5-day versus 10-day incubation time in suspected prosthetic joint infection: a prospective laboratory study.

Optimising laboratory processes is paramount in differentiating prosthetic joint infection (PJI) from non-infectious causes of joint dysfunction. However, the optimal duration of incubation of PJI samples remains unclear in the modern laboratory. This study explored whether an increased incubation time in the routine processing of samples from suspected PJI, from 5-7 to 10 days, would significantly increase the yield of clinically relevant bacteria. A total of 280 prosthetic joint samples from 53 patients were included prospectively over a 3-month period. After an initial standard 5-day incubation plus additional 2 days subculture of thioglycolate broth in high-risk samples (current standard in this laboratory), incubation was extended until day 10. From the 280 samples included, 190 organisms were isolated. Potentially significant additional pathogens that were not detected with standard approaches were found in 5 of 280 samples (2%) with prolonged incubation, though the overall clinical significance of these organisms was unclear. Of all non-significant growth, the majority (70%) occurred on extended incubation. In conclusion, extending incubation of prosthetic hip and knee joint samples from 5-7 to 10 days routinely was associated with increased risk of isolating contaminating organisms without significant benefit. However, further studies are needed to clarify the utility of extended incubation in upper limb joints.