Diagnostics of Tuberculosis

An insight into Gene Expert

Dr. Muhammad Yahya NooriAssistant Professor

Department of Pathology

Focal Person for Provincial Tuberculosis Reference Lab Sindh

DIMC

DUHS

Tuberculosis

Second only to HIV/AIDS

One in three humans carries the Bacilli

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The Cost

2013

1.5 Million Deaths

9 Million New Cases

Drug Sensitive TB

$100-500/case

MDR TB

$9000-48000/case3

Pakistan

Burden of Disease

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Pakistan

New Cases

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Diagnosis of tuberculosis

Latent Infection Active tuberculosis

Smear examination

Solid and liquid culture

Identification

Susceptibility testing methods

TST

IFN- techniques

Molecular methods

-Detection

-Identification

-Detection of resistance

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finddiadnostics.org

Example of Rif-Sensitive Profile – 5 probes are

positive

MTB/Rif Assay design

Molecular

Beacon

Target

Hybrid

Each probe is labeled with a different fluorophore,

permitting simultaneous detection of the presence

of wild type.

The MTB assay target is the 81 bp region (RRDR) of the rpoB gene.

SPC

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Xpert MTB/RIF Assay

Satisfactory results were obtained in the studies

that were performed in 2010:

• Sensitivity in smear-positive culture-positive specimens:

99%

• Sensitivity in smear-negative culture-positive specimens:

90%

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WHO Evaluation on Xpert MTB/RIF Assay-2011

• Average detection time:– Solid culture: >30 days

– Liquid culture: 17 days

– Microscopy: 1 day

– Xpert MTB/RIF: <1 day

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WHO Evaluation on Xpert MTB/RIF Assay-2011

• Xpert MTB/RIF assay:– Analytical sensitivity: 5 genome copies/purified

DNA

or 131 cfu/ml sputum

(10-100 cfu/ml sputum for culture)

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Processing

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Xpert MTB/RIF Assay Meta-Analysis Study

• Average sensitivity for detection of rifampicin resistance: 94.1%

• Average specificity for detection of rifampicin resistance: 97.0%

• Average sensitivity in extra-pulmonary specimens: 80.4%

• Average specificity in extra-pulmonary specimens : 86.1%

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Current Practices

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All smear Positive new

treatment cases that remain +ve

two months after treatment

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All Hospitalized patients who

have presumptive TB

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Presumptive smear negative

cases at high volume centers

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Health care workers with TB

symptoms

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First line treatment failures

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MDR-TB contacts

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TB/HIV

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History of ATT

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Thank you

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