Occult Prosthetic Joint Infection (PJI) is Rare in Patients with Staphylococcus aureus Bacteremia (SAB)

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Authors: Tande AJ, Palraj B, Berbari EF, Osmon DR, Baddour LM, Steckelberg JM, Wilson WR, Sohail MR.
Mayo Clinic, Rochester, MN

Title: Occult Prosthetic Joint Infection (PJI) is Rare in Patients with Staphylococcus aureus Bacteremia (SAB)

Background: SAB is a life threatening condition that may lead to metastatic infection. There is paucity of data regarding the risk of occult S. aureus PJI (SA-PJI) in patients presenting with SAB.

Hypothesis/Purpose: How often does PJI occur in patients with a joint arthroplasty (JA) in place at the time of SAB?

Methods: This was a retrospective cohort study of all patients with a JA at time of their first episode of SAB seen at our institution between 6/1/2006- 6/30/2011. SAB was defined as > 1 positive blood culture or 1 positive blood culture with signs and symptoms of infection. SA-PJI was defined using previous criteria for PJI that includes periprosthetic culture, along with supportive criteria or independent review by two investigators.  PJI was defined as early (<90 days), delayed (90-365 days) or late (>365 days) based on time from most recent surgery.

Results: We identified 109 patients with 183 JA (range 1-6 JA per patient) at the time of SAB. The median age was 72 years (range 22-95 years) and 37% were female. SA-PJI was present in 52 (47.7%) of 109 patients and 60 (32.8%) of 183 JA.  Only 1 of 60 infected JA had no signs or symptoms suggestive of PJI on history or exam. SA-PJI occurred in 3 (18.8%) of 16 nosocomial, 21 (44.7%) of 47 community onset health-care associated and 28 (60.9%) of 46 community onset episodes of SAB (p = 0.01). All 3 of the nosocomial SA-PJI were within 180 days of surgery and were the likely source of SAB. SA-PJI was defined as early in 13 (21.7%), delayed in 7 (11.7%) and late in 40 (66.7%) JA. In patients without early or delayed SA-PJI, SA-PJI was diagnosed in 32 (36%) of 89. Among the 46 patients who survived to hospital discharge, there were 2 SA-PJI (4.3%) diagnosed 179 and 319 days after the resolution of SAB. Neither had evidence of SA-PJI at the time of SAB.

Death occurred within 6 months after SAB in 8 (15.4%) of 52 patients with SA-PJI and 21 (36.8%) of 57 patients without SA-PJI (p=0.01).

Discussion: SA-PJI is frequent in patients with existing JA and concomitant SAB. However, occult SA-PJI, without signs or symptoms suggestive of PJI, is rare. Hematogenous seeding of JA is unlikely in cases of nosocomial SAB.  Evaluation for PJI should focus on symptomatic patients with community onset SAB.

Conclusion: SA-PJI is common in patients with a JA in place during SAB, but occurs predominantly in patients with community onset SAB.