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RECENT ADVANCES IN DIAGNOSIS OF TUBERCULOSIS

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RECENT ADVANCES IN DIAGNOSIS OF TUBERCULOSIS

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TRADITIONAL TESTS AND RECENT DIAGNOSTIC MODALITIES FOR TUBERCULOSIS WITH EMPHASIS TO MOLECULAR DETECTION TECHNIQUES, DRUG SENSITIVITY ASSESMENT IN INDIAN PERSPECTIVE

TRADITIONAL TESTS AND RECENT DIAGNOSTIC MODALITIES FOR TUBERCULOSIS WITH EMPHASIS TO MOLECULAR DETECTION TECHNIQUES, DRUG SENSITIVITY ASSESMENT IN INDIAN PERSPECTIVE

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RECENT ADVANCES IN DIAGNOSIS OF TUBERCULOSIS

  1. 1. RECENT ADVANCES IN DIAGNOSIS OF TUBERCULOSIS CHAIRPERSON: PROF. KRISHNENDU ROY SPEAKER: ANGAN KARMAKAR (JUNIOR RESIDENT)
  2. 2. Approach towards microbiological diagnosis of TB
  3. 3. FLUORESCENT MICROSCOPY • increased sensitivity • LED microscopy advantages? • low power consumption • no dark room requirement disadvantages? • dye toxicity
  4. 4. RAPID CULTURE METHODS • BACTEC 460 (Middle brook7H9 broth) • Mycobacteria growth indicator tube (MGIT)
  5. 5. ADVANTAGES OF MGIT • all type of specimens • continuously monitored • positive signals over 10-12 days • non-radiometeric • cheaper than BACTEC
  6. 6. DST using rapid culture method MODS • microscopic-observation drug-susceptibility assay • antituberculous drug containing Middle brook 7H9 broth • growth (cord formation) detected using inverted light microscope • time to detection- 7 days • sensitivity 95% & specificity 100%
  7. 7. IFN-γ release assays • in vitro assays • whole blood incubated with TB antigens • measures interferon (IFN-γ) released by sensitized T cells • measures immune reactivity to M.tb
  8. 8. QuantiFERON TB Gold • combines IFN-γ release technology with the diagnostic power of synthetic TB-specific peptides (ESAT-6 and CFP-10) to provide the best available method of diagnosing TB infection • FDA-approved for the detection of LTBI, 2001.
  9. 9. Analysis of IGRA report Positive IGRA • person has been infected with TB bacteria. additional tests are needed to determine if the person has latent TB infection or TB disease Negative IGRA: • latent TB infection or TB disease is not likely
  10. 10. MOLECULAR METHODS • uncultivable or difficult to culture • HIV infected patients • rapid result • quantitative information (viral load) • susceptibility testing (drug resistance) without culture
  11. 11. • may not differentiate active infection as DNA from a dead organism during antibiotic treatment can be detected and amplified by PCR • High cost
  12. 12. Nucleic acid amplification tests • amplify M. tuberculosis-specific nucleic acid sequences using a nucleic acid probe • sensitivity at least 80% in most studies • Require 10 bacilli/ml of given sample • specificity 98% to 99%.
  13. 13. Molecular methods used in NAAT For amplification • Polymerase chain reaction • Transcription mediated amplification • Loop mediated isothermal amplification • Ligase chain reaction • Real time PCR For detection: • Electrophoresis • Line probe assay • Real time detection
  14. 14. Xpert MTB/RIF • detects M. tuberculosis & rifampicin resistance conferring mutations • unprecedented sensitivity-smear negative, culture positive specimens • provides results directly from the sputum within 100 minutes • Endorsed by WHO since 2011
  15. 15. Xpert MTB/RIF from different samples SAMPLE SENSITIVITY SPECIFICITY Sputum 88% 99% Lymph node aspirate 84.9% 92.5% CSF 79.5% 98.6% Pleural fluid 43.7% 98.1% Gastric lavage/aspirate 83.8% 98.8% Source: WHO policy update for Xpert MTB/RIF(2013)
  16. 16. Line probe assays • PCR/hybridization technique to identify Mycobacterium Tuberculosis • identify drug-resistant strains by detecting the most common single nucleotide polymorphorisms associated with resistance
  17. 17. GenoType®MTBDR/MTBDRplus Detects: • Genotype • RIF resistance • INH resistance
  18. 18. • In-house PCR tests are widely used in the developing countries • The line probe assays (LPA) are suitable only for national or regional level laboratories because of its complexity and bio safety requirements
  19. 19. Molecular DST- candidates? • Patients suspected or at high risk of having drug- resistant TB • very ill patients • HIV infected patients • who do not get better while taking standard first- line therapy
  20. 20. Lateral flow urine lipoarabinomannan (LF-LAM)assay • From urine of active TB patients • Endorsed by WHO in 2015 • Only for HIV patients- seriously ill/ low CD4 count
  21. 21. WHO policies
  22. 22. Cost of diagnostic tests TESTS ZN microscopy LED-FM microscopy Gene Xpert MTB/RIF Line probe assay Solid culture Liquid culture COST in INR 50 100 600 1500 250 600 Source: Medicine update 2016 (Association of Physicians, India)
  23. 23. “Unite to end TB” (World TB day 2016 theme)

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