Prosthetic joint infections are challenging to diagnose because current detection methods are often unreliable. Culturing periprosthetic tissue specimens is a routine method used in the diagnosis of prosthetic joint infections, however, sensitivity is less than ideal. Traditionally, these cultures are done using agar and broth cultures.
Mayo Clinic researchers conducted a study to compare the sensitivity and specificity of inoculation of periprosthetic tissue specimens into blood culture bottles with standard agar and broth cultures, applying Bayesian latent class modeling (LCM) in addition to applying the Infectious Diseases Society of America criteria for prosthetic joint infection. The study, published in mBio, compared the sensitivity and specificity of different culture techniques alone and in combination and assessed time to positivity.
“Previous studies evaluating culture of periprosthetic tissue specimens in blood culture bottles showed promising results, but they were either very small studies or lacked comparative data,” said Robin Patel, M.D., Chair of the Division of Clinical Microbiology at Mayo Clinic and Consultant in the Clinical Microbiology and Infectious Diseases Laboratories. Dr. Patel is also the senior author on this paper. “We wanted to demonstrate that this could be a suitable method in comparison to the conventional microbiological methods already used in our hands, mainly because we thought it would be easier for the laboratory.”
Study design was also an important factor. Given the unknown prevalence of prosthetic joint infections and limitations of conventional microbiological techniques, traditional statistical methods may lead to miscalculation of the true sensitivities of new tests and true disease prevalence. In this study, researchers used the Bayesian LCM, a statistical method that overcomes potential flaws of traditional analysis. This was the first study to apply Bayesian LCM in prosthetic joint infection diagnosis.
“In identifying the Bayesian LCM method, we worked with statisticians at Mayo and in Australia. This method has not been widely applied to infectious disease diagnostic tests,” said Dr. Patel.
The study results demonstrated that the use of blood culture bottles for periprosthetic tissue culture increased the sensitivity of prosthetic joint infection diagnosis, compared to the standard method of agar plate and thioglycolate broth culture. Further, this improved sensitivity was similar in both Bayesian LCM and traditional analysis.
Overall, periprosthetic tissue culture in blood culture bottles resulted in eight additional microbiological diagnoses of prosthetic joint infection.
“In beginning this study, we simply wanted to show that this new method was equal to conventional strategies. We were surprised to detect bacteria in more infected patients by using the blood culture bottle method than we did using conventional approaches,” said Dr. Patel. “Procedurally, we thought this method would be easier in the laboratory, but we didn’t expect the results to be better.”
In addition to improved sensitivity, time to microorganism detection was faster using the automated blood culture bottle system. The system facilitated the diagnosis of prosthetic joint infection within the first 24 hours of surgery in most cases.
Dr. Patel noted that the way cultures are done varies significantly from laboratory to laboratory, including how specimens are collected, transported, processed, what volume is inoculated, and which media are used. This study analyzed one component of that process and optimized it.
“We chose to use blood culture bottles because it semi-automates the process, and we thought this would streamline it and make it more efficient. However, the fact that it not only improved the process but also improved sensitivity of prosthetic joint infection diagnosis went beyond our expectations,” said Dr. Patel.
Mayo Clinic in Rochester now uses this method as its diagnostic strategy for culturing periprosthetic tissue specimens.
“We made this change because it has improved our overall testing procedures, and it improved the impact on our patients,” added Dr. Patel.
By Andy Tofilon