Clinical diagnostic value of simultaneous amplification and testing for the diagnosis of sputum-scarce pulmonary tuberculosis

BACKGROUND

Since 20% of pulmonary tuberculosis (PTB) patients are asymptomatic, the early detection of PTB is a challenge particularly in sputum-scarce patients and diagnostic accuracy based solely on clinical characteristics and chest X-ray/CT scans are not always satisfactory. The AmpSure simultaneous amplification and testing method for the detection of Mycobacterium tuberculosis (SAT-TB assay) is an alternative approach to diagnose PTB. In the present study, we analyzed the usefulness of the SAT-TB assay for PTB diagnosis in sputum-scarce patients.

METHODS

A total of 840 patients were prospectively enrolled for PTB diagnosis with bronchial alveolar lavage fluid (BALF) used as the samples for the SAT-TB assay. Of these, 536 had a definite diagnosis of PTB confirmed by positive microbiology culture, or clinical diagnosis of active PTB following anti-TB treatment with a favorable response.

RESULTS

The SAT-TB assay showed a 76.44% agreement with the culture test. The sensitivity and specificity of the SAT-TB assay were 50.75% and 94.73%, respectively. The sensitivity of SAT-TB was significantly higher than that of BALF cultures (21.64%) (X² = 49.1503; P < 0.001) and smears (4.48%) (X² = 175.2315; P < 0.001). The specificity of SAT-TB was slightly lower than that of BALF cultures (98.25%) (X² = 2.0727; P = 0.150) and smears (98.25%) (X² = 2.0727; P = 0.150). The accuracy rates were 63.87% for SAT-TB, 44.50% for BALF cultures and 29.84% for BALF smears.

CONCLUSION

The high accuracy of the SAT-TB assay indicated that active PTB is present and anti-TB treatment is strongly recommended regardless of smear and culture test results for sputum scarce active PTB suspected patients when BALF SAT-TB is positive.

Using simultaneous amplification and testing method for evaluating the treatment outcome of pulmonary tuberculosis

Background

To evaluate the utility of Simultaneous Amplification and Testing (SAT-TB) Method for monitoring anti-TB treatment response.

Methods

Serial morning sputum specimens were obtained from 377 active pulmonary tuberculosis (PTB) cases at baseline, weeks 2, months 2, 5 and 6 (newly diagnosed patients) or 8 (previously treated patients) for AmpSure assay, smear fluorescence microscopy (FM) and BACTEC MGIT 960 culture assay.

Results

After treatment of 2 weeks, sputum culture was positive in 280 patients (74.27%). Among whom, 219 patients tested positive for SAT-TB assay and 143 patients smear FM positive. The detection rate of SAT-TB (78.21%) was significantly higher than sputum FM (51.07%, χ2 = 45.128, P < 0.001). At the end of the second month of treatment, 157 patients (41.64%) were still culture-positive, 115 patients of them SAT-TB positive and 79 smear FM positive. The difference of detection rate between SAT-TB (73.25%) and sputum FM (50.32%) was significant (χ2 = 17.480, P < 0.001). When patients underwent five months of treatment, 65 patients (17.24%) with sputum culture positive was defined as treatment failure. Among whom, 60 patients (92.31%) were SAT-TB positive and 38 patients (58.46%) were smear FM positive. The detection rate of SAT-TB assay was significantly higher than sputum FM (χ2 = 17.333, P < 0.001).

Conclusion

Results of AmpSure assays for monitoring treatment responses can be obtained without waiting for the results of BACTEC MGIT 960 assays and most patients with treatment failures could be detected after 5 months.