2004 Abstract : BS 3

Authors: Sirianni V, Rao N, Muder RR, Mook W, Crossett L, Sinha RK, Miller E.

Title: Prospective Evaluation of Criteria for Accurate Microbiological Diagnosis of Prosthetic Joint Infection

Addresses:UPMC Presbyterian Shadyside, School of Nursing Building, Second Floor, 5230 Centre Avenue, Pittsburgh, PA 15232-1381

Purpose: To prospectively evaluate the criteria for accurate microbiological diagnosis of prosthetic joint infections (PJI).

Methods: Seventy adult patients with a clinical and ancillary diagnosis such as elevated ESR, CRP, and radiographic evidence of PJI were followed prospectively from January of 2001 to April of 2003 for the accuracy of microbiological diagnosis. Accurate microbiological diagnosis was defined as two or more intra-operative cultures for the same organism. Patients had multiple cultures obtained during surgery under aseptic conditions which included joint fluid, acetabulum, femoral membrane/bone, and tibial membrane/bone. The cultures were processed for aerobic, anaerobic, AFB, fungal, and others.

Results: Mean age of patients was 64 years (range 31-86 years). There were 43 females and 27 males, 18 hip joints and 52 knee joints. Pathogens identified included Staphylococcus species (47%), Streptococcus species (17.1%), gram negative bacilli (5.7%), Candida species (4.2%), and Enterococcus species and anaerobes (1.4% each). More than one pathogen was identified in 15.7 % of patients while 5.7% had no pathogen identified. Fifty-eight of seventy patients (83%) had two or more positive cultures for the same organism. Six patients (8.5%) had only one positive culture. Five of six pathogens were unlikely to be contaminants. Three of five had candida, one of five MRSA, and one of five Enterococcus. One other patient had a coagulase negative Staphylococcus species. Six patients had one positive culture for coagulase negative Staphylococcus in addition to other pathogens seen in more than one culture. Six other patients (8.5%) had negative cultures despite multiple samples. Only one of these six had received pre-operative oral cephalexin for four days.
All sites of sampling were equally sensitive in percentage of yield of positive cultures.

Discussion: Accurate microbiological diagnosis of PJI infection may be difficult despite multiple tissue cultures. Additional methods including sonication of the implants and PCR may need to be explored for accurate documentation of the pathogen prior to treatment.

Significance: The significance of a single positive intra-operative culture for coagulase negative Staphylococcus species is unclear.