New diagnostics and their potential role

in TB screening/diagnostic algorithms

31 May, 2011

Fuad Mirzayev MD, MPH

TB Diagnostics and Laboratory Strengthening unit, Stop TB Department

WHO, Geneva

2

New diagnostics and their potential role in TB

screening/diagnostic algorithms

New diagnostics and their role in TB diagnostic

algorithms

New diagnostics and their potential role in TB

screening algorithms

Year Technology Turnaround timeSensitivity

gain

Before 2007ZN microscopy

Solid culture

2-3 days

30-60 daysBaseline

2007Liquid culture / DST

Rapid speciation15-30 days

+10% compared

to LJ

2008Line Probe Assay

(1st line, R & H)2-4 days

At this time for

SS+ only

2009LED-based FM 1-2 days

+10% compared

to ZN

Conditional

2009

In-house DST

(MODS, CRI, NRA)15-30 days 1st line only

Endorsed

2010

Automated NAAT

(TB, R)90 minutes

+40% compared

to ZN;~LJ

a) early diagnosis & care; b) smear-negative TB; c) rapid MDR/XDR detection

WHO policies 2007-2010

4

MGIT LJ PCR FM ZN

102 104 105 106 107103101

1+ 2+ 3+ 4+

Xpert MTB/RIF Sensitivity Specificity

TB detection 91% 99%

Rifampicin resistance 95% 98%

5

WHO policy recommendations

1. Xpert MTB/RIF should be used as the initial diagnostic test in

individuals suspected of having MDR-TB or HIV-associated TB.

(Strong recommendation)

2. Xpert MTB/RIF may be considered as a follow-on test to microscopy in

settings where MDR-TB or HIV is of lesser concern, especially in

further testing of smear-negative specimens. (Conditional

recommendation acknowledging major resource implications)

Remarks:

• These recommendations apply to the use of Xpert MTB/RIF in sputum specimens (including pellets from

decontaminated specimens). Data on the utility of Xpert MTB/RIF in extra-pulmonary specimens are still

limited;

• These recommendations support the use of one sputum specimen for diagnostic testing, acknowledging

that multiple specimens increase the sensitivity of Xpert MTB/RIF but have major resource implications;

• These recommendations also apply to children, based on the generalisation of data from adults and

acknowledging the limitations of microbiological diagnosis of TB (including MDR-TB) in children;

• Access to conventional microscopy, culture and DST is still needed for monitoring of therapy, for

prevalence surveys and/or surveillance, and for recovering isolates for drug susceptibility testing other

than rifampicin (including second-line anti-TB drugs).

5 20 80 500-1000Samples per

shift

GeneXpert

Xpert

MTB/RIF

Xpert MTB/RIF assay

Positioning in tiered health system

SubDistrictLevel

MicroscopyLevel

CommunityLevel

ReferenceLabs

RegionalLabs

DistrictLevel

•Surveillance•Reference methods•Network supervision

Resolution testing (screening-test negativedrug resistance)

•Screening•Passive case finding•Detect and treat

•Clinical screening•Primary care

Integrated NAAT +40% /2h

LED FM +10%

LC / DST 15d/ 30d

LPA Rif / INH 2dSC / DST 30d / 60d

ZN 2-3d

LC / DST 15d / 30d

In house DST (MODS, NRA, CRI) Special settings and conditions

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Practical considerations: preferential pricing

and eligible countries*

Afghanistan Chile Ghana Libya Pakistan Sudan, South

Albania China Grenada Lithuania Palau Suriname

Algeria Colombia Guatemala Macedonia Panama Swaziland

Angola Comoros Guinea Madagascar Papua New Guinea Syria

Antigua and

Barbuda

Congo, Democratic

Republic of the Guinea-Bissau Malawi Paraguay Tajikistan

Argentina

Congo, Republic of

the Guinea, Equatorial Malaysia Peru Tanzania

Armenia Costa Rica Haiti Maldives Philippines Thailand

Azerbaijan Cote d'Ivoire Honduras Mali Romania Timor-Leste

Bangladesh Croatia India Mauritania Russia Togo

Belarus Cuba Indonesia Mauritius Rwanda Tonga

Belize Djibouti Iraq Mexico Saint Kitts and Nevis Tunisia

Benin Dominica Jamaica

Micronesia,

Federated States of Saint Lucia Turkmenistan

Bolivia Dominican Republic Jordan Moldova

Saint Vincent & the

Grenadines Tuvalu

Bosnia and

Herzegovina Ecuador Kazakhstan Mongolia Samoa Uganda

Botswana Egypt Kenya Montenegro Sao Tome and Principe Ukraine

Brazil El Salvador Kiribati Morocco Senegal Uruguay

Bulgaria Eritrea Korea, North Mozambique Serbia Uzbekistan

Burkina Faso Estonia Kosovo Myanmar (Burma) Seychelles Vanuatu

Burundi Ethiopia Kyrgyzstan Namibia Sierra Leone Venezuela

Cambodia Fiji Laos Nauru Solomon Islands Vietnam

Cameroon Gabon Latvia Nepal Somalia Western Sahara

Cabo Verde Gambia, The Lebanon Nicaragua South Africa Yemen

Central African

Republic Gaza and West Bank Lesotho Niger Sri Lanka Zambia

Chad Georgia Liberia Nigeria Sudan Zimbabwe

GeneXpert System4 module

with desktop – 17’000 $

with laptop – 17’500 $

Cartridge – 16.86 $

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*as of 19.02.2011

Risk based assessment for Xpert MTB/RIF

testing

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Where MDR-TB or HIV associated TB is of

lesser concern

Sputum smear microscopy remains the recommended first test for TB

diagnosis.

Pre-test screening strategies for Xpert MTB/RIF testing of all persons

suspected of having TB should be considered to optimise assay

performance, efficiency and cost and will be strongly dependent on

available resources and the TB screening and diagnostic algorithms at

country level. Chest X-ray example

TB suspects who test negative with sputum smear microscopy should

be referred (or their sputum sent) for further testing, preferably in a

facility with Xpert MTB/RIF, if there is clinical suspicion of TB and

sufficient resources are available.

Individuals with sputum smear-positive microscopy results do not need

to be tested with Xpert MTB/RIF unless they belong to the risk groups

described above.

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Xpert MTB/RIF – diagnostic test

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Xpert MTB/RIF TB Detection Rifampicin resistance

Sensitivity 91% 95%

Specificity 99% 98%

• Low bio-safety requirement

• Sensitivity close to culture

• High specificity

• Rapid (< 2 hrs)

• Portability

• Ease of use

• Running costs

• Infrastructure needs

• PPV of R resistance

depends on

prevalence of R

resistance

• R resistance ≠ MDR-TB

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Predictive values of Xpert MTB/RIF for

rifampicin resistance

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50%

PPV

NPV

Rifampicin resistance prevalence

71%

84%

90%

Sensitivity = 95%

Specificity = 98%

Management of patients with MDR-TB

Rifampicin resistance is a reliable proxy for MDR-TB in high burden

settings. Patients with confirmed resistance to rifampicin by Xpert

MTB/RIF should therefore be started on appropriate MDR-TB

treatment immediately and treatment adjusted based on the results of

further DST.

Testing cases not at risk for MDR-TB in low MDR-TB prevalence

settings will result in low PPV for rifampicin resistance, and require that

rifampicin resistance detected by Xpert MTB/RIF be confirmed by

conventional DST or LPA.

TB patients identified by Xpert MTB/RIF without rifampicin

resistance should be referred for appropriate first-line anti-TB

treatment.

If TB is not detected, the individual should be referred for further

investigations and clinical management according to national

guidelines.

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New diagnostics and their potential role in

TB screening/diagnostic algorithms

New diagnostics and their role in TB diagnostic algorithms

New diagnostics and their potential role in TB screening

algorithms

• Medical diagnosis refers to the process of attempting to determine

and/or identify a possible disease or disorder and the opinion reached

by this process that allow medical decisions about treatment and

prognosis to be made.

• Screening - the examination of a group of usually asymptomatic

individuals to detect those with a high probability of having or

developing a given disease.

The American Heritage® Medical Dictionary Copyright © 2007

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Asymptomatic

?

?

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Screening for TB and/or MDR-TB?

Wilson and Jungner criteria for screening

1. Condition is an important health problem for individual and community.

2. There is accepted treatment for patients with the disease.

3. The natural history of the disease should be adequately understood.

4. There should be a latent or early symptomatic stage.

5. There should be a suitable and acceptable screening test.

6. Facilities for diagnosis and treatment should be available.

7. There should be an agreed policy on whom to treat as patients.

8. Early treatments has more benefit than treatment started later.

9. The cost should be economically balanced.

2007 2008 2009 2010 2011 2012 2013 2014 2015 2016

Dis

tan

ce

fro

m P

ati

en

ts

Peripheral Lab

First Referral Level

Community Health Care

Abbreviations

DST: Drug Susceptibility Test

NAAT: Nucleic Acid Amplification Test

LTBI: Latent TB Infection

POC: Point of Care

MODS: Microscopic observation drug-

susceptibility

NRA: Nitrate reductase assay

CRI: Colorimetric redox indicator assay

LED: Light-emitting diode

LPA: Line probe assay

Technologies or processes endorsed by WHO

Technologies for which WHO review is in process

10-40%

70%

95%

% A

ccess a

fter 5

years

TB Diagnostics pipeline

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The TB test we need*

• Detection of active TB in adults regardless of HIV

status

• Improved diagnostic in children

• Result that allow decision on treatment initiation

• Patient can receive result on the same day

• Point-of-care: easy to perform in peripheral health

centres

• DST (preferable but not minimum requirement)

• Need to aim to a NON-sputum sample base test

*MSF led POC TB test consultation, 2009

Test specification Minimum required value Xpert MTB/RIF specificationsComparison with

minimum requirementMedical decision Treatment initiation Treatment initiation. Selection of regimen Exceeded

Sensitivity for smear-positive culture-positive† PTB in adults

≥95% 99.8% (95% CI: 99.0–100; three Xpert MTB/RIF assays compared with culture†)

Satisfied

98.2% (95% CI: 96.8–99.0; one Xpert MTB/RIF assay compared with culture†)

Sensitivity for smear-negative culture-positive† PTB in adults

60–80% 90.2% (95% CI: 84.9–93.8; three Xpert MTB/RIF assays compared with culture†)

Satisfied

72.5% (95% CI: 42.4–79.9; one Xpert MTB/RIF assay compared with culture†)

Specificity in adults without TB ≥95% 98.1% (95% CI: 96.6–98.9; three Xpert MTB/RIF assays compared with culture)

Satisfied

99.2% (95% CI: 98.1 –99.6; one Xpert MTB/RIF assay compared with culture)

Sensitivity for all types of 80% compared with culture No data available No data

TB in children 60% for probable TB

Specificity in children 95% compared with culture No data available No data

90% for probable TB

Time to results ≤3 hours 2 h Exceeded

Throughput 20 tests per day by one laboratory staff member

Total hands-on time of 2 min Satisfied

Total daily throughput depends on the size of the instrument

Specimen type Adults: urine, oral, breath, venous blood and sputum

Sputum Satisfied

Children: urine, oral and capillary blood

May work with other samples except for venous blood

Sample preparation Maximum of three steps Two steps: sputum liquefaction followed by loading of sample into cartridge

Exceeded

Ability to use approximate volumes Cartridges can handle a variety of starting volumes Satisfied

Preparation that is not highly time sensitive

Preparation not highly time sensitive Satisfied

Biosafety level 1 Biosafety level 1 Satisfied

Comparison of Xpert® MTB/RIF characteristics

with the proposed minimum set of specifications

for point-of-care diagnostic tests for TB.

Table adapted from

Expert Rev Mol Diagn. 2010 Oct;10(7):937-46.

Xpert(®) MTB/RIF for point-of-care diagnosis of

TB in high-HIV burden, resource-limited

countries: hype or hope?

Van Rie A, Page-Shipp L, Scott L, Sanne I, Stevens

W.

The criteria were developed at a March 2009 workshop organized by Médecins Sans Frontières.

Test specification Minimum required value Xpert MTB/RIF specificationsComparison with

minimum requirement

Number of samples One sample per test No batching of samples needed Satisfied

Readout Easy to read; simple ‘yes’, ‘no’ or ‘invalid’ answer

Simple and color coded Satisfied

Readable for at least 1 h Readout stored on a computer Satisfied

Waste disposal Simple burning, no glass, environmentally acceptable

Plastic reagent tubes can be recycled, cartridges canbe incinerated

Satisfied

Controls Positive control included in test kit Positive control included in test kit Satisfied

Reagents All reagents in a self-contained kit All reagents in a self-contained kit Satisfied

Kit contains a sample collection device and water (if needed)

Kit contains a pipette to transfer liquefied sputum from container to cartridge

Satisfied

Storage/stability Shelf-life of 24 months, including reagents

Maximum shelf-life of 14 months Not satisfied

Stable at 30ºC and at higher temperatures for shorter time periods

Reagents stable at temperatures >30ºC for a short time. System operates in temperatures of 15–30ºC

Satisfied

Stable in high humidity environments System works in ambient humidity of of 10–95% Satisfied

Instrumentation‡ Instrument with no maintenance required

Requires annual maintanance Not satisfied

Fits in a backpack The smallest, one cartridge version comes with a laptop and fits in a backpack

Satisfied

Power requirement Can work on battery power systems, but cannot yet work on battery power

Low power requirement compared with other PCR Not satisfied

Training 1 day maximum training Approximately 1 day of training required Satisfied

Can be performed by any health worker

No special skills required other than basic computer skills

Satisfied

Cost <US$10 per test after scale-up Currently USD16.86 per cartridge May not be satisfied

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