MTB/RIF Ultra was developed to improve on the sensitivity of the original MTB/RIF assay for detecting tuberculosis (TB), especially in smear-negative and HIV-associated cases. MTB/RIF Ultra uses multiple genetic targets and has a lower limit of detection, resulting in improved sensitivity. It can detect TB at very low bacillary levels and has categories for trace results that may need confirmation with a second specimen. MTB/RIF Ultra performance for rifampicin resistance detection is similar to the original assay. Proper recording of patient category and results is important for correct interpretation. Countries need monitoring plans as they transition cartridge types to track impact.

1. Xpert® MTB/RIF Ultra
Information

2. Why was MTB/RIF Ultra developed
MTB/RIF assay challenges:
• Sensitivity in smear negatives and HIV associated TB low
• 60-70% - sub-optimal
• Sensitivity for Rif resistance determination
• Limitations: May miss some Rifs

3. MTB/RIF MTB/RIF Ultra
Diagnosis MTB complex MTB complex
Resistance Detects rifampicin resistance
as a surrogate for MDR-TB
Detects rifampicin resistance as
a surrogate for MDR-TB
Amplification for TB
detection
Single target: rpoB core
region
Multi-copy target: RpoB core
region
Insertion elements: IS6110 +
IS1081
Resistance detection Real-time PCR
5 probes bind to RpoB gene
Melting curve
4 probes bind to RpoB gene
Sputum input 2ml 2ml
PCR reaction 25ul 50ul
Assay TAT 112min 65-87min
Limit of detection 131cfu/ml 16cfu/ml
Cost 9.98USD 9.98USD
Short pieces of DNA,
occurs multiple times
in genome, conserved
in MTBC

4. Melting curve analysis: If a mutation is present, dsDNA (probe + TB DNA) dissociates sooner than if
‘normal’ DNA present
Temperature
Fluorescence
Mutant
’Normal’
Mixed population
The range of Tm is known for mutant
and normal
Tm mutant TB Tm normal TB
Principle of detection

5. Results for Ultra MTB categories
Category MTB/RIF Xpert Ultra Interpretation
Not detected X X No TB detected
High X X TB detected
Med X X TB detected
Low X X TB detected
Very low X X TB detected
Trace X Trace amounts MTB detected
MTB not detected = neither of multi-copy target probes are positive but SPC is positive (valid)
MTB detected = one or both probes for multi-copy target are positive and at least two rpoB
probes positive

6. New category: MTB trace
• A new result category on Gx
• Trace = Improved sensitivity = Lowest bacillary burden detected
• One or both probes for multi-copy targets are positive with Ct <37
and no more than one RpoB probes have a Ct<40
Considerations for interpretation of trace results:
• In HIV-positives, children and EPTB = TB positive
• If in a patient with no-risk of HIV or previous history of TB = repeat
test on new specimen
• if trace detected on repeat = TB positive

7. Results for Rifampicin
Semi-Quant
category
Xpert MTB/RIF Xpert Ultra
High, Med, low Rif resistance detected /not
detected
Rif resistance detected / not
detected/ indeterminate
Very low Rif resistance detected/ not
detected /indeterminate
Rif resistance detected/ not detected/
indeterminate
MTB trace detected Rif indeterminate
Rif susceptible = all four RpoB probes have identifiable melt temperatures in wild type (normal)
profile
Rif resistance = all four RpoB probes have identifiable melt temperatures and at least one is a
mutant profile

8. Performance of Ultra vs MTB/RIF
FIND multi-site evaluation
• N=1520 adult pulmonary TB suspects
• Overall, Ultra = 5% higher sensitivity
• Especially in smear-neg/culture pos and HIV-pos
• Overall, Ultra = 3% lower specificity
• Especially in patients with history of TB who may have ’dead’ bacteria still in
system
• Lab cross-contamination
• Therefore, if result is a Trace detected – repeat with new specimen
• Sensitivity for Rif detection similar to MTB/RIF at ~100%

9. Considerations for implementation
• Cartridges visually identical except for label: MTB/RIF vs Ultra
• Shelf-life currently @8months
• By Q3 2017 expected to be 12months
• Targeted shelf-life = 24months
• Gx software requirements:
• Dx systems: 4.7b or higher required
• Infinity systems: 6.4b or higher
• Can be used on Omni platform

10. Clinical Recording and reporting
• Current guidelines apply:
• Ultra can be used as initial diagnostic for all adults and children with symptoms of
pulmonary TB
• Can also be used in selective EPTB specimens: CSF, lymph nodes and tissues
Considerations:
• Critical that clinicians can monitor which assay was done
• Request forms/or Gx test notes/ or reporting system: Critical to capture patient
category due to differences in interpretation of results (trace)
• Categories: PLHIV, children, EPTB
• If a trace detected –request a 2nd specimen
• Also need a specimen numbering system to monitor repeat tests

11. Note: Different algorithm followed for
trace results depending on patient
category – therefore important to:
• Incl patient category
• Prompt request for 2nd specimen
• Label 2nd specimen for same
patient
Ref: GLI. Planning for country transition to Xpert® MTB/RIF Ultra Cartridges. April 2017

12. Key indicators required for countries to monitor transition
process
• Site readiness (software upgrade, training and documentation)
• Stock levels of Xpert MTB/RIF and Ultra
• Availability of Ultra in regions or at sites, as per schedule
• # of Xpert MTB/RIF and Ultra tests performed
• # of cartridges expiring before use
* Additional lab indicators:
• # and proportion of trace calls by patient category
• # and proportion of patients whose 1st specimen produces a trace call and
receives a repeat test
• # and proportion of patients who receive repeat test and result is MTB
detected/Rif R

13. Clinical impact monitoring
• Total #of TB cases diagnosed, disaggregated by patient group (e.g., PLHIV,
children, extrapulmonary TB)
• # and proportion of bacteriologically confirmed TB cases, disaggregated by
patient group
• # and proportion of bacteriologically confirmed TB cases with DST results for
rifampicin
• # and proportion of patients who are initiated on treatment according to the
national algorithm

14. References
• GLI. Planning for country transition to Xpert® MTB/RIF Ultra Cartridges. April 2017
• WHO. Meeting Report of a Technical Expert Consultation: Non-inferiority analysis of Xpert MTB/RIF Ultra
compared to Xpert MTB/RIF. 2017
• WHO. Frequently asked questions about the WHO Technical Expert Consultation findings on Xpert® MTB/RIF
Ultra. March 2017