Background/Purpose:

Little is known about the effects of antibiotic therapy on synovial and blood culture results among patients with prosthetic joint septic arthritis (PJSA). In this study we aimed to determine this effect.

Methods:

We conducted a retrospective study of patients 18 years and older admitted to a single tertiary care center between 1998 and 2015 with culture-positive PJSA. Only patients with serial blood or synovial fluid cultures who received appropriate antibiotic treatment (i.e. matched to the bacterial antibiogram) and in whom the timing of initiation of antibiotic therapy was documented were included in this study. Time to conversion of cultures from positive to negative was calculated calculated using Kaplan-Meier and Cox regression models. Log Rank (Mantel-Cox) test and Wald test were used to compare survival curves among groups and versus the general tendency. A p-value < 0.05 was considered significant for all tests.

Results:

Among patients with culture- positive PJSA serial blood and synovial fluid cultures were obtained in 38 (36.5%) and 66 (63.5%) patients, respectively. Mean number of samples per patient was 10.7 and 2.4 for blood and synovial fluid cultures, respectively. Vancomycin was the most commonly prescribed antibiotic and was administered to 84.5% of the patients. Median time to conversion from positive to negative culture results was significantly longer for synovial fluid cultures compared with blood cultures (147.7 vs 34.9 hours; p-value <0.001).Median time of conversion from positive to negative blood culture results varied significantly for the top 3 pathogens; Coagulase negative Staphylococcus (CONS), methicillin-sensitive Staphylococcus Aureus (MSSA), methicillin-resistant Staphylococcus Aureus (MRSA) (22.9 vs 47.1 vs 37.3 hours, respectively; p= 0.006).

Conclusion:

To our knowledge, this is the first study to demonstrate the effect of antibiotic administration on blood and synovial culture positivity over time. Blood cultures appear to be more sensitive than synovial fluid cultures to the effect of antibiotics. We also were able to demonstrate that the effect of antibiotics on blood culture sterility varies between different bacterial pathogens.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-effect-of-antibiotic-therapy-on-positive-culture-results-among-patients-with-prosthetic-joint-septic-arthritis/