Pre-operative asymptomatic bacteriuria: a risk factor for prosthetic joint infection?

Infection is a rare complication following implantation of prosthetic material into a joint. The impact of asymptomatic bacteriuria (ASB) before elective operations and the subsequent risk of prosthetic joint infection (PJI) are not well understood.

To assess the prevalence of ASB amongst patients undergoing total arthroplasty of the hip and knee; and to determine the rates of PJI diagnosed within two years of the arthroplasty and if ASB is an independent risk factor for developing PJI.

Patients who had total/unicondylar knee or total hip arthroplasty were reviewed retrospectively over a five-year period. Pre-operative urine samples within one year of surgery were analysed, and those with ASB were identified. The primary outcome was PJI within the first postoperative year.

In total, 5542 patients were included. Of these, 4368 had a pre-operative urine culture recorded. The prevalence of ASB was 140 of 4368 (3.2%). The overall PJI rate was 56 of 5542 (1.01%). Of those with PJI, 33 had a pre-operative urine sample recorded. The infection rates were 5% (seven of 140) in the ASB group, 0.61% (26 of 4228) in the no-ASB group and 1.96% (23 of 1174) in the group without a urine sample (P < 0.001). The ASB isolate was the same micro-organism as the PJI isolate in one of the seven cases.

The association between ASB and PJI is statistically significant, but the urine isolates did not relate to the isolates in the prosthetic joint, suggesting that the relationship is unlikely to be causal.