C-200. Detection of Mycobacterium tuberculosis in Respiratory and Non-Respiratory Clinical Specimen Using the BACTEC MGIT960 Culture and DNA Strand Displacement Amplification (SDA) Assay

M. A. M. El-Sweify1,2, M. A. Soliman3;
1Faculty of Med., Suez Canal Univ., Egypt, Riyadh, SAUDI ARABIA, 2KFMC-FOM, Riyadh, SAUDI ARABIA, 3Al-Iman Gen. Hosp., MOH, Riyadh, SAUDI ARABIA.

Background: NAATs provide significant tools for diagnosis of pulmonary TB (PTB); but thier efficacy in diagnosis of extrapulmonary TB (EPTB) is still questionable. Isolation of Mycobacterium tuberculosis (MTB) with antibigram are advantages which favor use of culture. We aimed to evaluate a combined use of BDProbeTec ET strand displacement amplification (SDA)(Beckton Dickenson, MD, US) and the BACTEC MGIT960 culture (as gold standard) (BD, MD, US) for MTB diagnosis in respiratory and non-respiratory clinical specimens. Methods: We collected 60 sputum and 54 non-respiratory samples: FNA(30), pus(6), CSF(10) and pleural fluid(8) from patients with clinical suspicion of TB. Samples were initially Z-N stained and screened for AFB. FNA specimens were Diff-Quik stained and examined for cytologic evidences of TB lesion. Specimens were cultured in MGIT tubes after decontamination/concentration procedure. Instrument-positive, AF-positive MGIT were subcultured to L-J slants. Growth was identified as MTB by niacin, nitrate and catalase tests. 114 specimens were analyzed by SDA as instructed by manufacturer, considering MOTA cutoff of 3400 for samples, and 5000 for IAC. Assays results were compared to clinical findings and some specimens were retested, when required. Data analysis was done in SSPS ver.14. Results: SDA identified MTB in 43/60 PTB and in 17/54 EPTB specimens. With PTB, SDA showed senisitivity of 93%, specificity 88%, PPV 95%, NPV 82% and diagn. accuracy 92%. For EPTB specimens, SDA sensitivity was 83%, specificity 94%, PPV 88%, NPV 92%, and diagn. accuracy 91%. SDA sensitivity was lower in AF-negative samples. On testing FNA, sensitivity (100%) and specificity (89%) of SDA were higher than other EPTB specimens. Conclusion: SDA and culture techniques could complement each other to achieve higher sensitivity and specificity than either tests alone. The 2 methods complement each other. Combined assays efficiently excluded MTB in patients with AF-positive samples when MOTT was suspected, and confirmed MTB in a number of suspected, culture-negative samples. SDA provided rapid diagnosis of MTB and higher sensitivity for diagnosis of EPTB in FNA, and was poorly sensitive in PF and CSF samples.