Advances in Dx of TB

Advances in Dx of TB - Advances in the Diagnosis of...

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Advances in the Diagnosis of Tuberculosis Gyanendra Agrawal
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19 century Until now (2007) still relying on direct smear (>10 4 bacilli/) culture (4-6 wks)
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Scope • Advances in microscopy • Advances in culture methods • Advances in IGRAs • Advances in NAA techniques • Advances in drug susceptibility testing • Advances in epidemiologic techniques
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Advances in bacilloscopy
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More sensitive (fluorescence microscopy on average 10% more sensitive p<0.001) Sensitivity greater in low grade positives Similar specificity (mean difference 0%;p=0.21) Takes less time Little difference between different flourescent staining techniques Limited data in HIV-TB coinfected pts. – available evidence suggests FM may be promising in this population Lancet Infect Dis 2006; 6:570–81
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Sputum processing methods • Cytocentrifugation • Bleach method – liquefaction of sputum with sodium hypochlorite and centrifugation • Treatment of sputum samples with zwitterionic detergent (carboxy-prophylbetaine (CB18)
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Sputum treated with bleach or NaOH and concentrated by centrifugation is more sensitive Sputum subjected to overnight sedimentation preceded by treatment with ammonium sulphate or bleach, is, on average, more sensitive, based on a small number of studies Specificity for processed smears is similar to that for direct smears Insufficient data to indicate whether the gains in sensitivity described above will also apply in patients with HIV infection Lancet Infect Dis 2006; 6:664–74
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Advances in culture methods
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Rapid culture methods • BACTEC system • MycobactGrowth Indicator Tube(MGIT) • MB/BacT system • Septi-check AFB method • ESP culture system II • Microscopic observation of broth/slide cultures
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BACTEC System • Radiometric method 14 C labeled palmitic acid added to liquid 7H12 medium • Detects M tb by metabolism rather than growth 14 CO 2 produced detected by specialized eqpt • Growth index (GI) measured • Results available in 7-14days (87-96%) Ind. J. Tub., 2003, 50,133
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MGIT • Mycobacteria growth indicator tubes • Capable of analyzing 960 specimen • Growth detection based on AFB metabolic O 2 utilization • Results available in 7-14 days • Cost effective for high load microbiology- labs
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MB/BacT system • Non radiometric continuous monitoring system • Automated • Based on colorimetric detection of CO 2 • Slightly longer time than BACTEC system (11.6 days vs 13.7 days) • Prone to contamination
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ESP culture system II • Based on detection of pressure changes in sealed broth culture bottle by gas production or consumption • Used in combination with solid medium not as a stand alone system
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Microscopic observation of broth culture • Rapid detection method • Relatively inexpensive • Suitable for endemic countries with high disease burden • Requires P2 Bio-safety cabinets • Relatively high technical skill required
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MODS assay • Microscopic observation drug susceptibility
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Advances in Dx of TB - Advances in the Diagnosis of...

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