LowTransmissibilityofMycobacteriumtuberculosisBasedonTimetoDetec6onfromPa6entswithanIni6alSputumPosi6vebyLiquidCulturebutNega6vebyNucleicAcidAmplifica6onTes6ngandAcid-FastBacilliStainSaahirKhan1,AudreyNakasone2,MinooGhajar3,MariamZhowandai3,SunitaPrabhu3,RickAlexander3,JulieLow4,EllenaPeterson2,andLauriThrupp1,2,5

1DivisionofInfec6ousDiseases,2ClinicalMicrobiologyLaboratory,5EpidemiologyandInfec6onPreven6on,UniversityofCaliforniaIrvineHealth,Orange,California3PublicHealthLaboratory,4TuberculosisControlDivision,OrangeCountyHealthcareAgency,SantaAna,California

Background

Tradi6onalguidelinesforde-isola6onofsuspectedpulmonaryTBcasesrequirethreerespiratoryspecimenscollectedandtestednega6vebyacid-fastbacilli(AFB)staining1,2(basedonstudiesshowingnega6veAFBindicateslowerorganismburdenandtransmissionrisk5,9)butrequirepa6entstospendtwoormoredaysincostlyairborneisola6onrooms3.

Ofconcernwiththisapproach,30-50%ofspecimensfromcultureposi6vepulmonaryTBcaseshavenega6veAFBstain4,and17%ofnewcasetransmissionsareacquiredfromAFB-nega6vecases5.

Recently,useofnucleicacidamplifica6ontests(NAAT)hasincreasedsensi6vityforTBdiagnosis6,promp6ngstudiessugges6ngde-isola6onaaeronespecimenwithnega6veAFBstainandnega6veNAAT5,6,11.

However,thisstrategymays6llmiss10-20%ofculture-posi6veAFBnega6vespecimens,promp6ngrecentguidelinessugges6ngtwospecimenswithnega6veNAATberequiredforde-isola6on7,8.

O’sheaetal.foundthat6metodetec6on(TTD)inliquidcultureof9ormoredaysindicatedlowertransmissionriskbederthanAFBstain10.

Figure1.Transmissionratesandpropor6onofsecondarycasesofac6vediseaseandlatentinfec6on(LTBI)stra6fiedby6me-to-detec6on.ReprintedfromO'Sheaetal.,ClinInfectDis,2014.

TTDhasnotyetbeenexaminedalongwithAFBstainandNAATtodetermineifTTDaddssubstan=vesupporttotheconceptofde-isola=onaAeronespecimennega=vebyAFBandNAAT.

PrincipalAim

ToevaluatewhetherpredictedTTD,incombina=onwithAFBandNAATtoiden=fylowriskcasesofsuspectedpulmonaryTB,supportsthegoalofde-isola=onaAeronespecimennega=veforAFBandNAAT

Methodology

Retrospec6veanalysisofacohortofall117pa6entstestedatU.C.IrvineHealth(UCI)from2013to2014and670pa6entstestedatOrangeCountyHealthCareAgency(OCHCA)in2014iden6fiedatotalof94Mtbculture-posi6vefirstrespiratoryspecimens(34atUCI,60atOCHCA).

EachspecimenwasassessedbyAFBgradewithKinyounstain,TTDinMGITculture,andNAATresultbyCepheidXpertonfresh(OCHCA)orstoredfrozen(UCI)rou6neconcentrates.

Figure2.KinyounstainforAFB(lea),MGITforliquidculture(middle),andCepheidXpertforNAAT(right).

Weanalyzedcorrela6onbetweenAFBgradeandTTDusingPearsoncorrela6oncoefficientwithStudent’st-testforgroupcomparisons.

Results

TimetoDetec=on,AFBGrade,andNAATResultfor94MtbCulture-Posi=veFirst-RespiratorySpecimens

Figure3.Timetodetec6onincultureversusAFBgradeandNAATresultfor94specimensanalyzed,stra6fiedintolowriskoftransmissionwithTTD>9daysandhighriskoftransmissionwithTTD<9days.

Among94totalspecimens,61specimens(65%)wereposi6vebyAFBstainandNAAT,andanaddi6onal21(22%)wereposi6vebyNAATalone,leaving12specimensofinterest(13%)thatwereposi6vebyMtbsolidculturebutnega6vebybothAFBstainandNAAT.

Figure4.94specimensanalyzedbyAFBgrade,NAATresult,andTTDwerestra6fiedintoahightransmissionriskgroup(pink)withposi6veAFBstainorposi6veNAATorTTDlessthan9daysandalowtransmissionrisk

group(blue)withnega6veAFBstain,nega6veNAAD,andTTDgreaterthanorequalto9days.

All12specimenswithnega6veAFBstainandNAAThadTTDof9daysorgreaterindica6nglowerriskofMtbtransmission(seeFigure3onlea).

TTDhasstronginverselinearcorrela6onwithAFBgrade(ρ=0.62).

Figure5.Mean6metodetec6onwithcorrela6ontosputumAFBgrade(errorbarsrepresentSEM)

Discussion/Conclusion

Nega6veAFBstainandNAATpredictTTDof9daysorgreater,allofwhichindicateloworganismburdenpredic6nglowtransmissionrisk.

Thesefindingssupportearlyde-isola6onaaeronespecimenwithnega6veAFBstainandNAATsincetheculture-posi6vesubsetofthesepa6entsallhadTTDof9daysorgreaterindica6nglowtransmissionrisk.

Addi6onally,inves6ga6onsofcontactswithprolongedexposureslikelyoveres6matetransmissionriskinhospitalseongswithbriefexposures.

UCInowallowsremovalofairborneisola6onforsuspectedpulmonaryTBcases(withoutcavi6es,miliarypadern,orimmunosuppression)aaeronespecimennega6vebybothAFBstainandNAAT.

***

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MtbCulturePosi6ve94(100%)

AFBStainPosi6ve61(65%)

AFBStainNega6ve33(35%)

MtbNAATPosi6ve21(22%)

MtbNAATNega6ve12(13%)

MtbTTD>9Days12(13%)

MtbTTD<9Days

0

Abstract57911

0

10

20

30

40TimetoDetec=o

n(Days)

AFBGrade:negneg1+2+3+4+TotalNAATResult:negposposposposposN=94

higherrisk

lowerrisk

NAAT TTD Smear Total0 1+ 2+ 3+ 4+

Nega6ve <9days 0 0 0 0 0 0 12≥9days 12 0 0 0 0 12

Posi6ve <9days 1 1 3 8 10 23 82≥9days 20 12 15 11 1 59Total 33 13 18 19 11 94

Rela6veRiskofTransmission:TTD>9days=0.4410

AFBnega6ve=0.19-0.225,9

lowerrisk higherrisk

TTD=-3.5*(AFB)+23DoublingTime=25hours

0

5

10

15

20

25

0 1+ 2+ 3+ 4+MeanTimetoDetec=o

n(Days)

SputumAFBGrade

References