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|Title: ||Nucleic acid amplification tests for diagnosis of smear-negative TB in a high HIV prevalence setting: a prospective cohort study|
|Authors: ||Davis, Lucian J|
Conville, Patricia S
Kovacs, Joseph A.
|Keywords: ||Nucleic Acid|
|Issue Date: ||2011 |
|Publisher: ||Public Library of Science|
|Citation: ||Davis J.L., Huang L., Worodria W., Masur H., Cattamanchi A., Huber, C., Miller, C., Conville, P.S., Murray, P., Kovacs, J.A. (2011). Nucleic acid amplification tests for diagnosis of smear-negative TB in a high HIV prevalence setting: a prospective cohort study. PLoS ONE 6(1)|
|Abstract: ||Background: Nucleic acid amplification tests are sensitive for identifying Mycobacterium tuberculosis in populations with positive sputum smears for acid-fast bacilli, but less sensitive in sputum-smear-negative populations. Few studies have
evaluated the clinical impact of these tests in low-income countries with high burdens of TB and HIV.
Methods: We prospectively enrolled 211 consecutive adults with cough $2 weeks and negative sputum smears at Mulago
Hospital in Kampala, Uganda. We tested a single early-morning sputum specimen for Mycobacterium tuberculosis DNA using two nucleic acid amplification tests: a novel in-house polymerase chain reaction targeting the mycobacterial secA1
gene, and the commercial AmplifiedH Mycobacterium tuberculosis Direct (MTD) test (Gen-Probe Inc, San Diego, CA). We
calculated the diagnostic accuracy of these index tests in reference to a primary microbiologic gold standard (positive mycobacterial culture of sputum or bronchoalveolar lavage fluid), and measured their likely clinical impact on additional
tuberculosis cases detected among those not prescribed initial TB treatment.
Results: Of 211 patients enrolled, 170 (81%) were HIV-seropositive, with median CD4+ T-cell count 78 cells/mL (interquartile
range 29-203). Among HIV-seropositive patients, 94 (55%) reported taking co-trimoxazole prophylaxis and 29 (17%)
reported taking antiretroviral therapy. Seventy-five patients (36%) had culture-confirmed TB. Sensitivity of MTD was 39%
(95% CI 28–51) and that of secA1 was 24% (95% CI 15–35). Both tests had specificities of 95% (95% CI 90–98). The MTD test
correctly identified 18 (24%) TB patients not treated at discharge and led to a 72% relative increase in the smear-negative
case detection rate.
Conclusions: The secA1 and MTD nucleic acid amplification tests had moderate sensitivity and high specificity for TB in a
predominantly HIV-seropositive population with negative sputum smears. Although newer, more sensitive nucleic acid
assays may enhance detection of Mycobacterium tuberculosis in sputum, even currently available tests can provide
substantial clinical impact in smear-negative populations.|
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