Rapid DST for TB ine Xpert MTBRIF M
Rapid DST for TB • ine Xpert MTB/RIF M. Tb positive RMPresistant M. Tb negative RMP susceptible Line Probe Assay (LPA) M. tb H, R sense H resist ��������� MDR 2 HRZE/4 HR R resist H, R resist NTM
Gene. Expert for TB • Advantages : • Short turn-around time of 2 hours • Simple because all are ready to use • High sensitivity to detect RMP resistant • Can be used to diagnose TB • Dis-advantages : • Detect only RMP resistant • High cost • Cost of instrument maintenance
Xpert MTB/RIF (Gene. Expert) • Gene. Expert principle • Hemi-nested PCR technique • Real-time PCR • Amplify rpo. B gene of RMP • Detecction of rpo. B mutation by probe BEACON in the same reaction • All reaction of PCR occurred in a cartridge , no any reagent is prepared • Fully automated
Should Rapid DST Be Done in Every New Patient Test : Sensitivity 96% Specificity 99% Prevalence MDR 2% Prevalence MDR 15% Phenotype MDR + total Rapid Pos 19 10 29 144 9 153 Neg 1 970 971 6 841 847 Total 20 980 1000 150 850 1000 PPV 65. 5% NPV 99. 9% PPV 94. 1% NPV 99. 3%
Line Probe Assay Method
BMC Infect Dis 2010
Rapid Drug Susceptibility Test (DST) • Indication for rapid DST • Risk factor(s) to carry drug resistance strains ( MDR rate >15%) • Closed contact to MDR-TB patient and develop TB • Smear positive after 3 months of treatment • Before changing regimen or adding any drug to treatment regimen • Suspected of NTM infection in smear positive patient
Definition of Poly-drug and MDR • Poly-drug : strain of M. tuberculosis that resist to two or more drugs and must not be resisted to Isoniazid and Rifampicin • MDR-TB : strain of M. tuberculosis that resist to Isoniazid and Rifampicin whether it resist to other drugs or not
Definition of XDR and TDR • XDR : strain of MDR-TB which also resisted to any one member of fluoroquinolones and one of injected anti-TB drugs : kanamycin, amikacin, capreomycin • PDR : strain of MDR-TB which also resisted to second line drug more than XDR • TDR : strain of MDR-TB which also resisted to six classes of second line drug (not international definition)
Diagnosis of DR/MDR/XDR-TB • Clinical signs and symptoms are not specific • Chest X-ray is not specific • Sputum examination should be positive at the time of diagnosis of M/XDR • Diagnosis of DR/MDR/XDR is based on result of drug susceptibility test • Standard susceptibility test take time of 8 -12 weeks to get result • Rapid DST is recommended by WHO but is only for INH and RMP
Identification of Mycobacteria • วธมาตราฐานในการ identification - ใช biochemical tests ใชเวลา 3 -6 เดอน - ม reproducibility ตำ • วธมาตราฐานใหม rapid identification - ใชวธทาง genotype ด sequence ของ DNA - ใชระยะเวลา 1 -2 วน
ผปวย ชาย ไทย อาย 59 ป (578031) • 18 กมภาพนธ 2557 Smear –ve, Culture –ve • 1 เมษายน 2557 Smear –ve, Culture –ve • 3 มถนายน 2557 Smear –ve, Culture –ve • 26 สงหาคม 2557 Smear –ve, Culture –ve • 23 กนยายน 2557 Smear –ve, Culture –ve • 21 ตลาคม 2557 Smear +ve, Culture +ve • 16 ธนวาคม 2557 Smear +ve, culture +ve • 30 มกราคม 2558 DST ตลาคม 2557 เปน M. tuberculosis sensitive ตอยาทกตว
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