Monday Gardam Screeningtb

8/12/2019 Monday Gardam Screeningtb

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Screening for

Tuberculosis

Screening for

Tuberculosis

Michael Gardam

TB Clinic,

Toronto Western Hospital

Annual risk is not constant

Riskofdevelopingactivedisease

Years after exposure

High Risk PeriodHigh Risk Period


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Risk factors for infection

Exposure Risk factors

Born in high-risk country

Occupation (e.g.healthcare worker)

Serious travel to high-risk country

Close contact of known active case

Age

Immunosuppression (HIV)

Estimated new TB cases (all

forms) per 100 000 population

No estimate

0-24

50-99

300 or more

25-49

100-299

Risk factors for progression

Canadian Standards, 2008


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nfection versus !isease

Latent Infection Active Disease

Burden oforganisms

Low Low-High

Symptoms None None-florid

Transmissibility Never infectious Often infectious ifpulmonary

Mantoux Usually positive Often positive

CXR 95% normal May be abnormal,Infiltrates, cavities

Therapy Optional preventativetherapy

4 drugs pendingsensitivities

TB screening

Warning: skin testing can be confusing"


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Screening guidance

#nl$ screen if $ou plan on doing something%ith the results

f looking for infection or disease, onl$ screen

those that ha&e a reason to be infected

Screening lo% pre&alence populations %ill result in

a high proportion of false positi&e results

Screening modalities

Chest radiograph screening detects'

(cti&e pulmonar$ disease

Those at high risk of de&eloping acti&e disease

Will miss most people with latent infection

Tuberculin skins testing and Interferon

Gamma Release Assays (IGRAs detect'

)atent infection


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Purified Protein !eri&ati&e

aka PP!, Tuberculin

!ifferent formulations used Contains appro*imatel$ + antigens

Man$ antigens are shared bet%een differentm$cobacteria

M tuberculosis comple*

M bovis

!CG strain of M bovis

-n&ironmental m$cobacteria

Contraindications

Se&ere reactions in

the past

Pre&ious documented

positi&e

-*tensi&e skin disease

Recent significant

&iral illness

"ot Contraindications

Pregnanc$

Recent &accination %itha killed &accine

BCG &accination histor$

Pre&iousl$ positi&e butnot documented

Children

Ho% to read a test

Measure induration using the pen techni.ue

n Canada' trans&erse diameter

n the /S, a&erage of the longitudinal and

trans&erse diameters

0 1mm is positi&e if'

2no%n recent contact

Significantl$ immunocompromise

Has fibronodular disease on their chest film

0 3 mm is positi&e for e&er$bod$ else


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Tuberculin skin test measurement

nterobser&er &ariabilit$ 4+51 mm6 ntra7obser&er &ariabilit$ 43587359 mm6

Biologic &ariabilit$ 4:8mm6

A change in up to #mm between tests can

$ust be due to %ariability&

Sensiti&it$ and specificit$

Sensiti&it$ cited as 9;< for latent TBinfection in health$ indi&iduals

!ecreased in immunocompromised

Sensiti&it$ closer to ;< for acti&edisease

Specificit$ influenced b$ BCG&accination, other m$cobacterial

e*posure

Boosting

#ccurs %ith remote BCG, at$pical

m$cobacteria, M. tuberculosis e*posure

Common 4178


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(ge at BCG &accination

and positi&e TSTs

nfanc$' no difference in positi&it$ bet%een&accinated and un&accinated after 1 $ears

Primar$ school' 317+1< remain positi&e after

3 $ears

nduration = 3>mm unlikel$ to be BCG

Iseman, 2000

18mm

Wh$ + step tests?

Perform a + step if'

@ou plan on testing the person again e5g5 atthe time of first hire

@ou %ant to increase the sensiti&it$ as muchas possible


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Con&ersion

!ifferent definitions'A mm' more sensiti&e, less specific

Ma$ be difficult to interpret gi&en &ariabilit$

3 mm' more specific, less sensiti&e

Best interpreted in conunction %ithepidemiolog$

e5g5, healthcare %orker in contact %ith acti&e case

Michael Gardam April 27,2005

Re&ersion

/p to >< of positi&e adults %ill becomenegati&e on repeat testing

More common in adults

More common in those %ith moderate siedinduration

More common in those %ith boosting -speciall$ if boosted after 8 or more serial tests

'ninterpretabletry not to retest

Summar$

Reading and interpreting skin tests is not so

simple5

This %as supposed to be fi*ed b$ nterferon

Gamma Release (ssa$s


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nterferon Gamma Release (ssa$s

4GR(s6

DE7based tests

Gardam et.al. Lancet ID

nterferon7gamma release assa$s

4GR(s6

FuantiE-R#D Gold

-)S(

T7Spot5TB

-)SP#T


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(ntigens used in latest GR(s

T%o M. tuberculosis proteins are used in theassa$s'

-arl$ secreted antigenic target 4-S(T7A6

Culture filtrate protein 3 4CEP736

Compare %ith =+ antigens in Tuberculin

Specific antigens for TB?

-S(T7A and CEP73 are also found in'

M. leprae

Wild t$pe M. bovis 4not the BCG strains6

M. marinum

M. kansasii

M. szulgai

M. flavescens

Reasonably common

in Canada

(d&antages of GR(s

More specific than the TST 4dont react to BCG

and most other non7TB m$cobacteria6

#nl$ 3 &isit re.uired

Do boosting phenomenon T7Spot5TB is more sensiti&e than the TST in

immunocompromised


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Hemodial$sis patients

Passalent et. al., CJASN 2006

!isad&antages

Same general issues as the TST in

immunocompromised i5e5 the$ dont %ork as

%ell

-*pensi&e, often patients must pa$ for them

)imited a&ailabilit$

Ha&e same issues %ith re&ersion as the TST

The risk of de&eloping acti&e TB in the settingof a positi&e GR( is unclear

!iscordant results

TST , GR( I

Secondar$ to BCG or false negati&e GR(?

TST 7, GR(

Poor sensiti&it$ of the TST or false positi&e GR(?

)ou cannot tell with certainty


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!iscordant results in lo% risk, BCG

&accinated population

!iscordant results in moderate or high

risk, BCG &accinated populations

GR( Summar$

(t present, the role for GR(s is relati&el$limited

testing lo% risk populations %ho ha&e recei&edBCG

mmunocompromised populations 4T7Spot5TB6

TST is generall$ the preferred test in Canada

Conclusions

Chest radiograph screening is best as an initial

assessment for pulmonar$ TB

TSTs and GR(s are best for detecting latent

infections

nterpreting TSTs is complicated

GR(s ha&e some ad&antages but are not

panaceas


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Monday Gardam Screeningtb

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