01-03-2013, 10:25 AM
Rapid molecular diagnosis of MDR / XDR-TB: line probe assay and beyond
[attachment=52253]
MDR and XDR-TB
• Almost half a million MDR-TB cases estimated
worldwide in 2006
• XDR-TB cases have now been confirmed in 49
countries (June 2008)
• Global XDR-TB Action Plan called for
accelerated implementation of rapid tests for
MDR-TB screening
Line probe assays (LPAs)
• Two commercial assays available
– Genotype MTBDRplus, INNO-LipA Rif.TB
– Validated for use directly from smear-positive
sputum (MTBDRplus) or from TB cultures
– Manual and automated systems
– rpoB for rifampicin resistance
– katG and inhA for isoniazid resistance
(MTBDRplus)
FIND South Africa demonstration
project
• Prospective cohort of cases/suspects
at high risk for MDR-TB
• Four provinces, each with one referral
laboratory performing rapid assays
• Genotype MTBDRplus compared with
gold standard (MGIT culture + DST)
• 20 000 sputum specimens from high
risk MDR-TB suspects
• Patient management based on rapid
assay result
• Conventional DST remains gold
standard if discrepancy with rapid
assay result
Demonstration project – preliminary data
analysis
• Patients enrolled between June and 31 Dec 2007, and
all laboratory results available on or before 31 Jan 2008.
• 10 793 sputum specimens from patients at risk for MDRTB
enrolled
• 2246 specimens tested by MTBDRplus
– 803 specimens tested directly from sputum (801
smear-positive specimens and 2 smear-negatives)
– 1443 specimens (1164 smear-negative and 279
smear-positive specimens) from positive MGIT
• Patients enrolled in 4 provinces
Results
• 92.0% (2032/2208) results were valid by MTBDRplus
assay
• 77.5% (1712/2208) results were valid by MGIT culture
and conventional DST (either MGIT DST or 7H11
proportion method)
• No significant difference in the proportion of valid
MTBDRplus results directly from sputum or from positive
MGIT cultures
• MTBDRplus gave results in 399 specimens with no DST
result (84%), 31 were MDR-TB
LPA cost
• Cost of MTBDRplus was less than conventional culture
and DST in South Africa
– Esp. direct from sputum
– From culture when % valid results considered
• Equipment costs
– $16, 000 for manual line probe assay system (excluding
equipment required for digestion-decontamination)
– Includes thermal cycler, shaking platform and waterbath, heating
block, sonicator, and microcentrifuge
• Automated GT Blot (Hain Lifescience)
– 14 352 Euro
Research needs for LPAs
• Evaluation of LPAs in algorithms in different
epidemiological settings
• Cost-effectiveness and cost-benefit of LPAs
• Use of LPAs in combination with culture for smearnegative
specimens
• Optimisation of DNA extraction methods, esp. from
paucibacillary specimens
• Specimen inactivation methods
[attachment=52253]
MDR and XDR-TB
• Almost half a million MDR-TB cases estimated
worldwide in 2006
• XDR-TB cases have now been confirmed in 49
countries (June 2008)
• Global XDR-TB Action Plan called for
accelerated implementation of rapid tests for
MDR-TB screening
Line probe assays (LPAs)
• Two commercial assays available
– Genotype MTBDRplus, INNO-LipA Rif.TB
– Validated for use directly from smear-positive
sputum (MTBDRplus) or from TB cultures
– Manual and automated systems
– rpoB for rifampicin resistance
– katG and inhA for isoniazid resistance
(MTBDRplus)
FIND South Africa demonstration
project
• Prospective cohort of cases/suspects
at high risk for MDR-TB
• Four provinces, each with one referral
laboratory performing rapid assays
• Genotype MTBDRplus compared with
gold standard (MGIT culture + DST)
• 20 000 sputum specimens from high
risk MDR-TB suspects
• Patient management based on rapid
assay result
• Conventional DST remains gold
standard if discrepancy with rapid
assay result
Demonstration project – preliminary data
analysis
• Patients enrolled between June and 31 Dec 2007, and
all laboratory results available on or before 31 Jan 2008.
• 10 793 sputum specimens from patients at risk for MDRTB
enrolled
• 2246 specimens tested by MTBDRplus
– 803 specimens tested directly from sputum (801
smear-positive specimens and 2 smear-negatives)
– 1443 specimens (1164 smear-negative and 279
smear-positive specimens) from positive MGIT
• Patients enrolled in 4 provinces
Results
• 92.0% (2032/2208) results were valid by MTBDRplus
assay
• 77.5% (1712/2208) results were valid by MGIT culture
and conventional DST (either MGIT DST or 7H11
proportion method)
• No significant difference in the proportion of valid
MTBDRplus results directly from sputum or from positive
MGIT cultures
• MTBDRplus gave results in 399 specimens with no DST
result (84%), 31 were MDR-TB
LPA cost
• Cost of MTBDRplus was less than conventional culture
and DST in South Africa
– Esp. direct from sputum
– From culture when % valid results considered
• Equipment costs
– $16, 000 for manual line probe assay system (excluding
equipment required for digestion-decontamination)
– Includes thermal cycler, shaking platform and waterbath, heating
block, sonicator, and microcentrifuge
• Automated GT Blot (Hain Lifescience)
– 14 352 Euro
Research needs for LPAs
• Evaluation of LPAs in algorithms in different
epidemiological settings
• Cost-effectiveness and cost-benefit of LPAs
• Use of LPAs in combination with culture for smearnegative
specimens
• Optimisation of DNA extraction methods, esp. from
paucibacillary specimens
• Specimen inactivation methods