# Rapid pathogen detection in synovial fluid of acute native joint infections in adults: a clinical evaluation of a novel automated multiplex polymerase chain reaction (mPCR) system

## TL;DR

A new rapid mPCR test was evaluated for diagnosing joint infections in adults and showed comparable accuracy to traditional methods but with faster results.

## Contribution

The study introduces a novel automated mPCR system for rapid pathogen detection in synovial fluid with clinical validation.

## Key findings

- The mPCR detected 13 novel microorganisms not identified by conventional culture.
- The mPCR showed substantial agreement (91% overall) with conventional culture methods.
- Combining mPCR and culture improved diagnostic accuracy slightly but not significantly.

## Abstract

Aim: The aim of this study was to investigate the diagnostic performance of a novel rapid multiplex polymerase chain reaction (mPCR) in adults with suspected acute native joint infection. Methods: This retrospective single-centre study included 143 patients with suspected acute native joint infection from February 2023 to May 2024. A septic arthritis was classified based on institutional criteria. The agreement between mPCR and conventional culture of synovial fluid (SF) was assessed by calculating the Cohen's
κ
coefficient. The diagnostic performance of mPCR was calculated, and the area under the curve (AUC) was compared with conventional culture of synovial fluid by using the
z
test. Results: When considering only microorganisms targeted by mPCR, this method detected 13 novel microorganisms in 13 cases compared to conventional culture, resulting in an overall agreement of 91 %, a positive agreement of 100 %, a negative agreement of 88 %, and a Cohen's
κ
 coefficient of 0.780. Of these 13 cases, 9 were classified as septic, with 6 (
n=6/9
, 67 %) on antibiotics prior to aspiration. When considering all microorganisms (including off-panel microorganisms), the overall percentage agreement between mPCR and conventional culture was 89 %, with a Cohen's
κ
 coefficient of 0.735, indicating substantial agreement. Sensitivity, specificity, PPV, NPV, LR
+
, LR
-
, accuracy, and AUC of mPCR were 45 %, 89 %, 90 %, 44 %, 4.21, 0.62, 59 %, and 0.671, and those of conventional culture were 40 %, 100 %, 100 %, 45 %, 0.60, 59 %, and 0.698. No difference in performance was observed between both methods (
p=0.183
). The combination of both techniques showed a sensitivity, specificity, PPV, NPV, LR
+
, LR
-
, accuracy, and AUC of 48 %, 89 %, 90 %, 46 %, 4.5, 0.58, 62 %, and 0.686. Conclusion: Given its comparable diagnostic performance and faster turnaround time relative to conventional synovial fluid culture, this novel mPCR can be recommended as a valuable adjunct in the diagnosis of septic arthritis in adults, particularly in patients with prior antimicrobial treatment.