Diagnosing TuberculosisOld and new tools

Anne Detjen, The Union

MicroscopyAcid-fast bacilli (AFB)

Ziehl andNeelsen (1892)

Tuberculin-Skin TestRobert Koch 1890 (Tuberculin)

Mendel (1909), Mantoux (1910)

Diagnosis of active TBDiagnosis of M. tuberculosis

infection (LTBI)

Over 100 years ago….

Microscopy remains the frontline tool for diagnosing active TB

But

New and exciting developments

Today

Microscopy

o Certain amount of bacilli needed for visibility

Diagnostic delay

Morbidity

Transmission

Sputum smear microscopy

Advantages

o Can be used at district levelo Simple and inexpensiveo Rapid detection of

infectious cases

o Smear positivity = Basis for recording and reporting of TB cases

Disadvantages

o Diagnostic delay: 5000-10,000 bacilli/ml

o Sensitivity 60-70% in HIV-uninfected adults

o Suboptimal in o HIV-infectedo Children 20%o Extrapulmonary TB (EPTB)

o Cannot distinguisho M. tuberculosis versus NTMo Dead or live M. tuberculosiso Drug-sensitive or resistant

Microscopy

o Sensitivity = correctly identified ‘sick’ peoplenumber of true positives

number of true positives plus number of false negatives

o Specificity = correctly identified healthy people

number of true negativesnumber of true negatives plus number of false positives

Measures of diagnostic accuracy

o Symptomso Chest radiography (or other imaging)o Immune response to M. tuberculosis

o Tuberculin Skin Testo Interferon-gamma Release Assayso Antibody tests

o Bacteriologic confirmation = gold standardand Drug susceptibility testing (DST) o Smear microscopyo Cultureo Nucleic acid amplicfication tests (NAATs)

What else?Approaches to diagnose TB

o Non-remitting cougho Night sweats o Fevero Fatigueo Organ-specific symptoms

Symptoms

Advantages

o Cheapo Can be done anywhere

Disadvantages

o Unspecifico No diagnosis

BUT: index of suspicion

Symptoms

o Unspecifico Certain characteristic features

o Cavitieso Lymph node enlargement in childrenoMiliary tuberculosis

o Remains pillar in diagnosis of TB in children

Chest radiography ~1910

Advantages

o Diagnosis of extent of disease and complications

Disadvantages

o Unspecifico Often difficult to accesso Equipment and personnelo Training in interpretation

Chest radiography

= Indirect assaysDetection of the host response to M. tuberculosis

o Cannot differentiate between active TB and M. tuberculosis infection (LTBI)

Immune-based Tests - Concept

o Sensitivity – false negative resultso Immune-compromised (HIV)o Severely ill (TB meningitis,

Miliary TB)o After vaccinations (e.g. measles)

or acute viral infectionso Specificity – false positive results

o BCG-vaccinatedo Infection with non-tuberculous

mycobacteria (NTM)

Tuberculin Skin Test, 1910

Advantages

o Basic test for M. tuberculosis infection

o Used for contact tracingo Risk assessment for active

TB

Disadvantages

o Not widely availableo Feasibility: Return visit

necessaryo Cross-reactivity

Tuberculin Skin Test

o Developed for detection of LTBIo Sensitized T-cells produce interferon-gamma after

stimulation with TB-specific antigenso Interferon-gamma/Interferon-gamma producing cells can be

measuredo Sensitivity similar to TST (70-90%)

o Increased in HIV-infected?o Children?

o Specificity superior to TST (>95%)o No cross-reactivity with BCG or

common NTM

Interferon-gamma Release Assays (IGRAs)

Advantages

o HIC: Superiority over TST (?)o LMIC: Value in HIV-infected,

children?

Recommended in many high income countries for detection of LTBI

Disadvantages

o Costo HR and lab requirementso No value for detection of

active TBWHO 25 October 2010:

Negative policy recommendation for low and middle income countries 2010

T SPOT TM.TB QuantiFERON®-Tb Gold In-Tube

Interferon-gamma Release Assays (IGRAs)

o Would be ideal point of care test (similar to HIV rapid test)

o Current commercial versions have suboptimal accuracy(and are yet widely used e.g. India)

First negative policy recommendation WHO 2011

Antibody Detection Tests

o Solid mediao Egg-based (Löwenstein-Jensen),

Agar-based (Middlebrook)o Time to detection: 3-4 weeks

o Liquid media (WHO 2007) o E.g. Bactec 460 (radiolabelled CO2) or Mycobacterial growth

indicator tube (MGIT) 960 (fluorescent indicator)o Time to detection: 10-14 dayso Yield +10% over solid mediao More prone to contamination

o Strain specification needed (Phenotypic, Genotypic)

Bacteriologic confirmation - Culture methods

o ‘Conventional’ = Culture of M. tuberculosis in the presence of anti-TB drugs to detect growth (resistant) or inhibition of growth (susceptible)o Direct DST = from specimeno indirect DST = from positive culture

= gold standard

Drug Sensitivity Testing

Advantages

o Gold standardo Increases case-finding (30-

50%)o Earlier detection than

microscopy (10-100 bacteria/ml)

Disadvantages

o Time (incl. DST)o Costo Lab and HR requirementso Biosafety requirementso Trainingo Maintenance of equipment

Bacteriologic confirmation

o Microscopy ~ 90 Million patient examinations/year (6% in high income countries)

o 50 Million chest radiographies (2/3 in Asia)o Culture:

o 17 Million cultures, 1/3 in HICo Of cultures performed in 22 high burden countries: 75%

are done in Brazil, Russian Federationo South Africa: > 90% of cultures on African continento 2.5% of incident TB cases in Asian and African HBC

receive DST

Use of current TB diagnostics

o Existing diagnostic tools are suboptimalo Accuracy (microscopy)

oHIV-infectedoChildren

o Time to diagnosis = Transmission o Feasibility in settings with limited resources

o FinancialoHumano Infrastructure

New diagnostics are urgently needed

Conclusion

NDWG 2009

Pathway for the development of new diagnostics

o Case detectiono Diagnosis of drug resistanceo Treatment follow-upo Diagnosis of latent TB infection

Development of new tools – What will a new test be used for?

Reference Laboratory

Regional/Referral Laboratory

Microscopy Laboratory

Health clinicSoph

istic

ation

of d

iagn

ostic

Patient accessWhere in the health system?

o Depends on the epidemiologic setting and health system contexto Add-on or replacement?

Each of these indications has different needs for a test – no ‘one-fits all’ solution

Desirable: o High accuracy in all patient groups

(smear positive, smear negative, HIV-infected, children, EPTB)o Easy to perform

o Little training, user-friendlyo Biosafety

o Close to the patient – point of care

Needs assessment

The diagnostic pipeline

o Fluorescent microscopyo 10% increased yieldo Recommended for intermediate level laboratories

(100+ smears)o Light-emitting diode (LED) fluorescence

microscopyo Accuracy comparable to conventional fluorescenceo Less power, can run on batteries, bulbs long half lifeo Alternative to conventional microscopy at high- and

low-volume laboratories

Improved microscopy

LAM = Lipoarrabinomannano Cell wall component of M. tuberculosiso Promising marker of active TB, found in urineo Potential for simple, non-invasive and safe

point-of care test?o Commercial assay available

Point of care diagnostic within reach?Urinary LAM Antigen detection

Minion, ERJ 2011

o Sensitivity of early non-commercial versions higher than pooled sensitivity of commercial versions

LAM Assays – Systematic review

o Microscopic Observation Drug Susceptibility (MODS)

o Using liquid mediumo Non-commercial, manual culture methodo Detection of

oM. tuberculosiso INH and RIF resistance

o Time to detection 7-14 days

www.modsperu.org

Simplified culture methods

o Simpleo Less expensiveo Modest training

requirementso Combines detection of

M. tuberculosis and DST

o Not standardizedo Local variations in

methodologyo Quality assuranceo Biosafety

WHO 2011: Recommended for MDR suspects as interim alternative

MODS

o Genotypic detection of M. tuberculosiso Allows for screening of common resistance-

causing mutationso Various commercial and

non-commercial NAATs have beenaround for >15 yearso Excellent specificityo Clinical sensitivity depends on bacterial

concentration: 50-80% in smearnegative

Nucleic Acid Amplification Tests (NAAT)

o Manual NAATo Detection of

oM. tuberculosiso INH and RIF resistance

o based on DNA strip technology. Three steps: DNA extraction, PCR and reverse hybridization

Recommended for detection of MDR TB on smear+ samples

Line Probe Assays (WHO 2008)

Advantages

o Results within hourso Fast detection of INH, RIF

resistanceo Excellent sensitivity and

specificity compared to conventional culture

Disadvantages

o Biosafety level 2 or 3o Limited use in

o HIV-infectedo Childreno (on positive cultures)

o Conventional culture (and DST) still needed for smear negative

Line Probe Assays

o Real-time PCR assayo Fully automated: No prior specimen processing

and DNA extraction neededo Detects M. tuberculosis and RIF resistanceo Highly accurate in smear + (99%) and smear -

(>80%) as well as HIV-infectedo Sensitivity for RIF resistance 95.1%, Specificity

98.4%o Results within 2 hours

Xpert MTB/RIF (WHO 2010)

Xpert MTB/RIF

Boehme et al. NEJM 2011

Potential for point of care test?• Cost• Electric supply

WHO policy statement:• Xpert MTB/RIF as initial diagnostic test in MDR suspects

or HIV-infected TB suspects• Follow-on test to microscopy in MDR or HIV low-burden

settings, further testing of smear negative samples District, Sub-district Level

Xpert MTB/RIF

• Exciting development in the area of new diagnostics

• Challenges:– Cost– Adoption at country level– Implementation and scale up

Still not optimal for– Vulnerable populations: Children– Extrapulmonary TB

Conclusions

Infants 43 %

Toddlers (1-5 years) 24 %

Adolescents (11-15 years) 15 %

Adults 5-10 %

Children 57-85%

modified from Sharma SK Lancet Infect Dis 2005; Marais Int J Tuberc Lung Dis 2004

Populations at risk - children

o Children account for approximately 15% of the annual incident cases globallyo Up to 40% of caseload in some areas

o TB in children contributes to global child morbidity and mortality

TB in children – a global challenge

Diagnostic challenges:o Different disease presentationo Difficulty to produce sputum

Alternative: gastric acido Paucibacillary TB

Diagnosis relies on composite of exposure history, symptoms, X-ray

TB diagnosis in children

Method Characteristics adults

Fluorescence microscopy/LED FM

• Improved sensitivity compared to light microscopy (5-10%)

MODS • Simple, rapid, inexpensive

NAAT• Multiple Commercial/In-house assays• Variable performance

LPA•High accuracy•Recommended in smear positive

Xpert MTB/RIF

Good performance in smear negative

Urine LAM•Highly variable•Improved sensitivity in HIV-infected

Volatile organic compounds

• Few data• Sub-optimal accuracy in adults (breath)

Method Characteristics adults Children

Fluorescence microscopy/LED FM

• Improved sensitivity compared to light microscopy (5-10%)

No data

MODS • Simple, rapid, inexpensive Very few data (2 studies)

NAAT• Multiple Commercial/In-house assays• Variable performance

• Few data

LPA•High accuracy•Recommended in smear positive

No data

Xpert MTB/RIF

Good performance in smear negative One study published

Urine LAM•Highly variable•Improved sensitivity in HIV-infected

No data

Volatile organic compounds

• Few data• Sub-optimal accuracy in adults (breath)

No data

New diagnostics in children

Policy

NDWG 2009

New diagnostics –from concept to public health implementation

WHO

WHO policy formulation

New diagnostics recent WHO policy recommendations

o 2007: Liquid culture and DST o 2008: Line probe Assayo 2010: Xpert MTB/RIFo 2011:

oNon-commercial culture and DST (MODS)o LED microscopyoNegative recommendation commercial

serodiagnostic tests o IGRAs

Limited data on patient outcomes and impact

High accuracy ≠ positive changes in outcomes

Challenges in developing policy guidance

o Functioning of new tool in different epidemiologic settings

o Functioning of new tool within diagnostic algorithms

o Cost effectivenesso Impact on health system and patientso Operational issues: training, maintenance, ,

supply chains, storage, waste management

Little information on

o WHO recommendation as basis for consideration

o Data from own or similar epidemiologic setting e.g. Brazil requests in-country validation and cost-effectiveness data

o Question remains: which tool or which combination of new tools

o Will there be another, better tool soon?

vanKampen PLoS One 2010

How does a country decide what to do?

o Negotiated reduced cost (WHO & FIND)o Rapid implementation documento Interim algorithmso Close monitoring of roll-out

http://www.who.int/tb/laboratory/mtbrifrollout/en/index.html

o TREAT TB: Monitoring of research

Global support – example Xpert

o Each policy document lists a number of open research questionso Test-specifico General related to implementation and impact

oCost effectivenesso Functioning of new test within health systemso Functioning within diagnostic algorithms (combination

of steps and tools)o Impact on patients (Cost, access)

Research – open questions

o Delay policy process?o Accompanying implementation process

o Optimize implementationo Inform national and global policy

o Different risk groups and disease manifestationso HIV-infectedo Childreno Extrapulmonary TB

Research

A framework for policy-relevant research – impact assessment

o Evaluation of new tools o under program conditionso as part of diagnostic strategies

o The impact of new diagnostic approaches should be measured on their ability to increase case detection. o Acceptable levels of sensitivity and specificityo Affordability (to the health system – and patients)o Accessibility (e.g. to all TB suspects)

o Impact on the society

Support decision making process for National TB Programs on which, when and how to implement new tools

Layer of Assessment

Layer 1:EFFICACY

ANALYSIS

Layer 2:EQUITY ANALYSIS

Layer 3:HEALTH SYSTEM

ANALYSIS

Layer 4: SCALE UP

ANALYSIS

Layer 5: POLICY ANALYSIS

Layer of Assessment

Kinds of question(s) being answered

Layer 1:EFFICACY

ANALYSIS

How well does new test work in terms of accuracy? How many additional cases will be identified?How many additional cases will actually start treatment / achieve cure / avoid

death?

Layer 2:EQUITY ANALYSIS

Who benefits from new test? (ambulant vs hospitalised, poor/less poor, men/women, adults/children)

Why do these benefits accrue? (level health system in which tests are deployed, change time to issue of results, change in patient costs)

Layer 3:HEALTH SYSTEM

ANALYSIS

What are the human resource implications of introducing the test? (training, number and cadre of staff)

What are the infrastructure implications? (equipment, lab layout, safety installations)What are the procurement implications? (reagents, consumables, documentation)What are the implications for quality assurance? (internal and external)

Layer 4: SCALE UP

ANALYSIS

What are the projected impacts of going to scale with the test? ega) cost savings to patients in relation to incomeb) cost savings to health providers / the health systemd) Effects on transmission of improved infection control as a result of test introduction

Layer 5: POLICY ANALYSIS

What other similar technologies are available or likely to become available?How do similar existing or emerging technologies compare in their projected

performance within each of the layers above?

Bertie Squire and Gillian Mann, Liverpool School of Tropical Medicine

Impact Assessment framework

o Exciting new diagnostics have been developedo Many open questions remain as to

o how these new diagnostics work in health systemso how they influence patient outcomes

o Need for more researcho Still needed:

o point of care diagnostics testo Better diagnostics for

Conclusions

Thank you!