Abstract
Introduction
Despite recent advances in the diagnosis of periprosthetic joint infection(PJI), identifying the infecting organism continues to be a challenge, with up to a third of PJIs reported to have negative cultures. Current molecular techniques have thus far been unable to replace culture as the gold standard for isolation of the infecting pathogen. Next- generation sequencing(NGS) is a well-established technique for comprehensively sequencing the entire pathogen DNA in a given sample and has recently gained much attention in many fields of medicine. Our aim was to evaluate the ability of NGS in identifying the causative organism(s) in patients with PJI.
Methods
After obtaining Institutional Review Board approval and informed consent for all study participants, samples were prospectively collected from 148 revision total joint arthroplasty procedures (83 knees, 65 hips). Synovial fluid, deep tissue and swabs were obtained at the time of surgery and shipped to the laboratory for NGS analysis (MicroGenDx). Deep tissue specimens were also sent to the institutional laboratory(Thomas Jefferson University Hospital) for culture. PJI was diagnosed using the Musculoskeletal Infection Society(MSIS) definition of PJI. Statistical analysis was performed using SPSS software.
Results
Fifty-five revisions were considered infected; culture was positive in 40 of these (40/55, 72.7%), while NGS was positive in 47 (47/55, 85.5%). Among the positive cultures, complete concordance between NGS and culture was observed in 33 cases (33/40, 82.5%). One case was partially discordant between NGS and culture, with culture detecting three organisms as opposed to one organism on NGS. One case showed complete discordance with NGS and culture detecting different organisms. Three patients with negative NGS results had positive cultures. In another two cases culture simply reported the gross morphology of the organism but the phenotype was not identified, while NGS was able to definitively identify an organism. Among the 15 cases of culture-negative PJI, NGS was able to identify an organism in 10 cases (10/15, 66.7%). These data are summarized in Figure 1.
Ninety-three revisions were considered to be aseptic; NGS exclusively identified microbes in 15 of 93 “aseptic” revisions (16.1%) and culture exclusively isolated an organism in 4 of 93 cases(5.3%). One case was positive on both NGS and culture, however the results were discordant from each other. The remaining cases (73/93, 78.5%) were both NGS and culture negative. NGS detected several organisms in most positive samples, with a greater number of organisms detected in aseptic compared to septic cases (6.8 vs. 4.0, respectively).
Discussion
NGS was able to detect a pathogen in two-thirds of culture-negative cases and demonstrated a high rate of concordance with culture in culture-positive cases. The rate of false positives was low compared to earlier studies using molecular techniques. Our findings also suggest that some cases of PJI may be polymicrobial and escape detection using conventional culture. NGS may be a useful adjunct for identifying the causative organism(s) in PJI, particularly in the setting of negative cultures. Further study is required to determine the significance of isolated organisms in samples from patients who are not thought to be infected.
