Diagnostic efficiency of Xpert MTB/RIF assay for osteoarticular tuberculosis in patients with inflammatory arthritis in China

BACKGROUND: Both osteoarticular tuberculosis (OA-TB) and inflammatory arthritis can lead to osteoarticular structural damage. These conditions exhibit similar symptoms, physical signs, and imaging features. Rapidly and accurately diagnosing OA-TB in patients with inflammatory arthritis presents a challenge to clinicians. Xpert MTB/RIF (Xpert) has been endorsed by the World Health Organization (WHO) as a rapid diagnostic tool for diagnosis of pulmonary and extrapulmonary TB. This study was designed to investigate diagnostic efficiency of Xpert for OA-TB in patients with inflammatory arthritis in China. METHODS: A total of 83 consecutive patients with inflammatory arthritis and suspected OA-TB were enrolled prospectively from June 2014 to May 2018. Demographic, clinical, and biological data were recorded. Xpert assay, smear microscopy examination (smear), BACTEC MGIT 960 (MGIT 960), pathological examination, and T-SPOT.TB test were performed for each patient who received operations. Diagnostic efficiency of Xpert was evaluated based on a composite reference standard (CRS). RESULTS: A total of 49 out of 83 patients with inflammatory arthritis and suspected OA-TB received operations, and 49 specimens were obtained during operations. According to CRS, 36 out of 49 patients with inflammatory arthritis were diagnosed with OA-TB, and 13 were not affected by the condition. Sensitivity of Xpert assay, smear, MGIT 960, pathological examination, and T-SPOT.TB test reached 66.70% (24/36), 25.00% (9/36), 30.55% (11/36), 47.22% (17/36), and 80.55% (29/36), respectively. Specificity of Xpert assay, smear, MGIT 960, and pathological examination was all 100% (13/13). Specificity of T-SPOT.TB test was 53.84% (7/13). Sensitivity of Xpert was higher than that of smear, MGIT 960 and pathological examination, but the sensitivity of Xpert was lower than that of T-SPOT.TB. Sensitivity of Xpert was statistically different from that of smear and MGIT 960 (P<0.001, P = 0.002), but the sensitivity of Xpert was not significantly different from that of pathological examination and T-SPOT.TB (P = 0.096, P = 0.181). Specificity of T-SPOT.TB was less than that of Xpert, smear, MGIT 960, and pathological examination, and the difference between them was statistically significant (P = 0.015). Among the 27 OA-TB patients with smear negative results, Xpert had the highest sensitivity, but sensitivity of Xpert was not significantly different from that of pathological examination and T-SPOT.TB (P = 0.413, P = 0.783). 2 of 36 OA-TB patients exhibited RIF resistance. Xpert was concordant with MGIT 960-based drug susceptibility testing (DST) in detecting rifampin (RIF) resistance. CONCLUSIONS: Xpert is an efficient tool with high sensitivity and specificity for OA-TB diagnosis in patients with inflammatory arthritis in high-TB prevalence countries. Compared with conventional methods, Xpert has two advantages: one is fast, and the other is able to provide RIF resistance information simultaneously.