Abstract
The prevalence and clinical implications of discordance between Xpert MTB/RIF assays and the AdvanSure TB/NTM real-time polymerase chain reaction (PCR) for bronchial washing specimens have not been studied in pulmonary TB (PTB) patients. The discordant proportion and its clinical impact were evaluated in 320 patients from the bronchoscopy registry whose bronchial washing specimens were tested simultaneously with Xpert MTB/RIF and the TB/NTM PCR assay for three years, and the accuracy of the assays, including the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV), were studied. The clinical risk factors for discordance and false positivity of assays were also studied. Among 130 patients who were clinically diagnosed with PTB, 64 patients showed positive acid-fast bacilli culture results, 56 patients showed positive results in molecular methods and clinician diagnosed PTB without results of microbiology in 10 patients. The sensitivity, specificity, PPV, and NPV were 80.0%, 98.95%, 98.1%, and 87.9%, respectively, for Xpert MTB/RIF and 81.5%, 92.6%, 88.3%, and 88.0%, respectively, for TB/NTM PCR. The discordant proportion was 16.9% and was higher in culture-negative PTB compared to culture-confirmed PTB (24.3% vs. 9.4%, p = 0.024). However, there were no significant differences in the clinical characteristics, regardless of the discordance. The diagnostic yield increased with an additional assay (7.7% for Xpert MTB/RIF and 9.2% for TB/NTM PCR). False positivity was less common in patients tested with Xpert MTB/RIF (1.05% vs. 7.37%, p = 0.0035). No host-related risk factor for false positivity was identified. The Xpert MTB/RIF and TB/NTM PCR assay in bronchial washing specimens can improve the diagnostic yields for PTB, although there were considerable discordant results without any patient-related risk factors.
Highlights
Tuberculosis (TB) is one of the most critical infectious diseases worldwide. [1,2] In TB-prevalent areas, early and accurate diagnosis is crucial for the timely initiation of treatment and prevention of lung deterioration and disease transmission
Bronchoscopic specimens from 320 patients were subjected to acid-fast bacilli (AFB) staining and culture, Xpert MTB/RIF, and TB/non-tuberculous mycobacterium (NTM) polymerase chain reaction (PCR) assay simultaneously
Sixty-four patients had culture-confirmed pulmonary TB (PTB) diagnosed microbiologically with the growth of M. tuberculosis and 66 patients had culture-negative PTB diagnosed with either Xpert MTB/RIF or TB/NTM PCR assay and/or a clinical decision based on the clinical course, therapeutic response, and radiologic findings. (Fig 1)
Summary
Tuberculosis (TB) is one of the most critical infectious diseases worldwide. [1,2] In TB-prevalent areas, early and accurate diagnosis is crucial for the timely initiation of treatment and prevention of lung deterioration and disease transmission. An AFB smear has high specificity and short turnaround time, but the low sensitivity is a challenge. [3,4,5] several molecular diagnostic methods for early detection of Mycobacterium tuberculosis have been developed. TB including commercial assay kits has high specificity and sensitivity as well as a short turn-around time. [9] Another molecular biological method Xpert MTB/RIF assay is a highly sensitive and specific diagnostic tool for TB diagnosis, and it can detect rifampin resistance simultaneously within 2 hours. [10] Despite highly sensitive and specific molecular methods being widely used in clinical practice to detect TB, there are few studies that show which assay is more accurate or whether they are complementary. TB including commercial assay kits has high specificity and sensitivity as well as a short turn-around time. [6,7,8] It can minimize contamination by allowing direct use of the clinical specimen in a closed system. [9] Another molecular biological method Xpert MTB/RIF assay is a highly sensitive and specific diagnostic tool for TB diagnosis, and it can detect rifampin resistance simultaneously within 2 hours. [10] Despite highly sensitive and specific molecular methods being widely used in clinical practice to detect TB, there are few studies that show which assay is more accurate or whether they are complementary. [11]
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