It is traditionally stated that around 80% of all periprosthetic joint infections (PJI) are caused by well-known gram-positive organisms such as Staphylococcus aureus. With the advances in diagnostic modalities and improved abilities to isolate infective organisms, we believe the organism profile causing PJI has changed over time and includes numerous other organisms that were either not recognized as pathogens and/or considered as contaminants.
We retrospectively reviewed the medical records of 1,363 patients with confirmed PJI (559 THA and 804 TKA) who received treatment at our institution between 2000 and 2019. Pertinent data related to demographics, microbiological findings, and outcome of treatment were collected. Organisms were differentiated using culture or confirmed by Matrix-Assisted Laser Desorption Ionization-time of flight (MALDI-tof) mass spectrometry. Statistical analysis included logistic regressions.
There was a total of 26 different species of organisms that resulted in PJI in our cohort. The rate of PJI caused by slow growing organisms, that are catalase negative, such as Streptococcal viridans (OR 1.244; 95% CI 1.036–1.494), Streptococcus agalactiae (OR 1.513; 95% CI 1.207–1.898), and Staphylococcus epidermidis (OR 1.321; 95% CI 1.191–1.466) has been increasing over time. In contrast, the incidence of PJI caused by coagulase-negative Staphylococcus (OR 0.954; 95% CI 0.927–0.981); resistant species (OR 0.962, 95% CI 0.931–0.995), and Gram-positive species (OR 0.94, 95% CI 0.914–0.966) decreased over time. Notably, there was a higher prevalence of Streptococcal PJI (OR 0.551, 95% CI 0.374–0.812) and culture-negative PJI (OR 0.652, 95% CI 0.478–0.890) seen in knees versus hips.
The rate of culture negative PJI also increased from 20% in 2000 to 28% in 2019. In the latter years of the study, very unusual list of organisms causing PJI were also identified.
This study reveals that the list of organisms causing PJI has expanded in recent years. The study also finds that some the slow growing organisms that were previously believed to be “contaminants” can and do cause PJI in a considerable number of patients. The number of culture negative cases of PJI has also increased at our institution over the years. There are a number of explanations for the latter finding, perhaps with the most important reason being liberal use of antibiotics that interferes with isolation of the infective organism.