title: Potential of two nucleic acid amplification assays for quantifying mycobacterial load in respiratory and non-respiratory specimens: a prospective study.
abstract: Quantification of bacillary load plays a critical prognostic role in tuberculosis patients. This study evaluated the potential of the Cepheid GeneXpert (GX) MTB/RIF and the BD ProbeTec system as quantitative assays. The time to positivity (TTP) measured by the Mycobacterial Growth Index Tube system was compared to the cycle threshold (Ct) of GX MTB/RIF and the Metric Other than Acceleration (MOTA) scores generated by the ProbeTec system. Out of 714 samples examined, 44 culture confirmed cases were identified. The Ct values in 21 respiratory samples showed a high linear fit with the TTP in liquid culture (Spearman's correlation coefficient r = 0.9, P value < 0.0001), which was not the case in 23 non-respiratory samples. In both types of specimens, the MOTA scores did not correlate with the TTP in liquid culture. This indicates the suitability of GX as a quantitative measurement of mycobacterial load in respiratory but not non-respiratory specimens.
authors.affiliation: Department of Medical Microbiology, College of Medicine, University of Dammam, Alkhobar 31952, Saudi Arabia. Electronic address: amalnimr@ud.edu.sa.
authors.forename: Amani Mansour
authors.initials: AM
authors.lastname: Alnimr
authors.affiliation: Department of Medical Microbiology, College of Medicine, University of Dammam, Alkhobar 31952, Saudi Arabia; Department of Medical Microbiology and Immunology, College of Medicine, Alexandria University, Alexandria, Egypt.
authors.forename: Manal Ismail
authors.initials: MI
authors.lastname: Hassan
mesh_terms: D058491:Bacterial Load; D001431:Bacteriological Techniques / Q000379:methods*; D001992:Bronchoalveolar Lavage Fluid / Q000382:microbiology; D004269:DNA, Bacterial / Q000302:isolation & purification*; D006801:Humans; D008168:Lung / Q000382:microbiology; D008198:Lymph Nodes / Q000382:microbiology; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification*; D021141:Nucleic Acid Amplification Techniques / Q000379:methods*; D011379:Prognosis; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013048:Specimen Handling; D013183:Sputum / Q000382:microbiology; D014376:Tuberculosis / Q000175:diagnosis*
chemical_list: D004269:DNA, Bacterial
keywords: GeneXpert; ProbeTec; Time-to-positive culture; Tuberculosis