Yoshiko Kawabe

Comparison of the sensitivity and specificity of two whole blood interferon-gamma assays for M. tuberculosis infection

OBJECTIVES To compare the sensitivity and the specificity of the QuantiFERON-TB Gold (QFT-G) and QuantiFERON-TB Gold In Tube (QFT-GIT) diagnostic tests for Mycobacterium tuberculosis infection. METHODS One-hundred patients with culture and/or PCR confirmed M. tuberculosis infection and 168 volunteers with no risk factors for M. tuberculosis infection were tested to estimate sensitivity and specificity, respectively. RESULTS Analysis of data from the tuberculosis (TB) patients with valid results found the sensitivity of QFT-GIT (92.6%, 87/94) to be significantly higher than that for the QFT-G test (81.4%, 79/97; p=0.023). The specificity of both QFT-GIT and QFT-G was 98.8% (CI: 95.1%-99.8%) with 2 of the 160 low risk subjects with valid results for both tests being positive. Data analysis confirmed the manufacturers recommended test cut-off as being optimal, but identified higher sensitivity could be obtained by using a lower cut-off, with only a moderate decrease in specificity. CONCLUSIONS The QFT-GIT test had enhanced sensitivity for detection of M. tuberculosis infection over the QFT-G test, whilst maintaining equivalent high specificity. The logistic benefits of the QFT-GIT test format, as well as its higher sensitivity, should enable enhanced TB control.

Diagnosis of Active Tuberculous Serositis by Antigen-Specific Interferon-γ Response of Cavity Fluid Cells

BACKGROUND To develop a more accurate methodology for diagnosing active tuberculous pleurisy, as well as peritonitis and pericardits of tuberculous origin, we established an antigen-specific interferon gamma (IFN-gamma)-based assay that uses cavity fluid specimens. METHODS Over a 19-month period, 155 consecutive, nonselected patients with any cavity effusion were evaluated. Study subjects were 28 patients with bacteriologically confirmed active tuberculous serositis and 47 patients with definitive nontuberculous etiology. Culture was performed for 18 h with fluid mononuclear cells in the supernatant of the effusion together with saline or Mycobacterium tuberculosis-specific antigenic peptides, early secretory antigenic target 6 and culture filtrate protein 10. IFN-gamma concentrations in the culture supernatants were measured. RESULTS In patients with active tuberculous serositis, antigen-specific IFN-gamma responses of cavity fluid samples were significantly higher than those of nontuberculous effusion samples. Area under the receiver operating characteristic (AUROC) curve was significantly greater for cavity fluid IFN-gamma response (AUROC curve, 0.996) than for cavity fluid adenosine deaminase and whole-blood IFN-gamma responses (AUROC curve, 0.882 and 0.719, respectively; P = .037 and P < .001, respectively). Although the AUROC curve was greater for cavity fluid IFN-gamma response than for background cavity fluid IFN-gamma level (AUROC curve, 0.975), the AUROC curves were not statistically significantly different (P = .74). However, multivariate logistic regression analysis revealed that cavity fluid IFN-gamma responses were significantly associated with the diagnosis, even after adjustment for background IFN-gamma level (adjusted odds ratio, 1.21; 95% confidence interval, 1.03-1.42; P < .001). CONCLUSIONS The cavity fluid IFN-gamma assay could be a method for accurately and promptly diagnosing active tuberculous serositis.

Biological and Molecular Characteristics of Mycobacterium tuberculosis Clinical Isolates with Low-Level Resistance to Isoniazid in Japan

ABSTRACT We reevaluated the BACTEC MGIT 960 antimicrobial susceptibility testing system (MGIT 960 AST) by using 1,112 isolates of Mycobacterium tuberculosis. When the results of MGIT 960 AST were compared with that of the proportion method using Ogawa medium (Ogawa PM), discrepant results were obtained for 30 strains with isoniazid, all resistant by MGIT 960 AST but susceptible by Ogawa PM. For 93% of the strains that produced discrepant results, the MIC was 0.4 or 0.8 μg/ml, showing resistance by the proportion method using Middlebrook agar plates. Furthermore, it was also established by analyses of the katG and inhA genes that strains resistant only by MGIT 960 AST have a low level of isoniazid (INH) resistance, indicating that MGIT 960 AST is a reliable method. Ninety-six strains were resistant to 0.1 μg/ml INH by MGIT 960 AST. When they were divided into three groups, Low-S (susceptible at 0.2 μg/ml), Low-R (resistant at 0.2 μg/ml), and High-R (resistant at 1.0 μg/ml), by Ogawa PM, 43.3% of the Low-S strains had mutations in the promoter region of inhA and no mutations were detected in katG codon 315, while 61.7% of the High-R strains had katG codon 315 mutations or a gross deletion of katG. These results suggest that mutations in inhA are associated with low-level resistance to INH and katG codon 315 mutations are associated with high-level resistance to INH. In addition, the analyses demonstrated some relationship of mutations in the inhA gene with ethionamide resistance for the Low-S strains, but not for the High-R strains.