Tuberculosis (TB), an infectious disease caused by Mycobacterium tuberculosis complex (MTC), remains one of the leading causes of death in the world. In Korea, the current prevalence of multidrug-resistant TB (MDR-TB) poses a major problem. The most common method for diagnosing TB in developing countries is sputum smear microscopy; however, the sensitivity of this test is relatively low and it usually requires well-trained laboratory staff. Cultures of MTC require up to several weeks in sophisticated facilities, such as Biosafety Level 3. Effective diagnostic techniques are necessary to control TB. In Korea, we evaluated a loop-mediated isothermal amplification (LAMP) assay targeting the hspX gene (TB-hspX-LAMP) of MTC. For clinical evaluation, culture confirmation, smear microscopy and TB-hspX-LAMP were performed on 303 sputum specimens obtained from suspected TB patients in Korea. The sensitivity, specificity, positive predictive value and negative predictive value of TB-hspX-LAMP were 71.1, 98.8, 91.4 and 95.1 %, respectively, compared with TB culture, which is the gold standard for diagnosis of TB. In contrast, the comparable values of smear microscopy were 24.4, 98.1, 68.8 and 88.2 %, respectively. Therefore, we concluded that TB-hspX-LAMP was superior to the use of smear microscopy for the detection of MTC in sputum specimens in clinical settings in Korea.
INTRODUCTIONTuberculosis (TB), an airborne infectious disease caused by Mycobacterium tuberculosis complex (MTC, Mycobacterium tuberculosis, Mycobacterium bovis, Mycobacterium africanum, Mycobacterium microti, Mycobacterium caprae, Mycobacterium canetti, Mycobacterium pinnipedii) (Behr et al., 1999; CDC, 2009), still remains one of the leading causes of death by infectious diseases worldwide. In 2013, 9 million people developed TB throughout the world; 1.5 million of this group died from it, of which 360 000 were human immunodeficiency virus-positive (WHO, 2014).Early, accurate diagnosis of MTC is important for the control of TB (Brodie & Schluger, 2005). The most common method for diagnosing TB in developing countries is sputum smear microscopy (George et al., 2011). Smear microscopy offers the advantages of rapid detection time and simplicity. However, the sensitivity of smear microscopy is relatively low and it requires well-trained laboratory staff.Culture methods can detect as few as 100 Mycobacterium cells per 1 ml specimen (Hofmann-Thiel et al., 2010) and TB culture is still considered the gold standard for the et al., 2003). The LAMP reaction produces stem-loop DNA structures with several inverted repeats and cauliflower-like structures with multiple loops. The products of amplified LAMP reactions can be measured by a change in the turbidity of the reaction mixture because magnesium pyrophosphate accumulates in the reaction mixture as a byproduct of the amplification reaction.The LAMP assay has several exceptional features compared with other TB diagnostic tools.(1) The LAMP assay uses four different primers to identify six distinct regions on...