<str<strong>on</strong>g>Guidel<strong>in</strong>es</str<strong>on</strong>g> <strong>on</strong> <strong>the</strong> Preventi<strong>on</strong> <strong>and</strong> C<strong>on</strong>trol <strong>of</strong> <strong>Tuberculosis</strong> <strong>in</strong> Irel<strong>and</strong> 2010HSE/HPSCRecommendati<strong>on</strong>s for <strong>the</strong> use <strong>of</strong> IGRAIGRA use should be c<strong>on</strong>sidered <strong>in</strong> c<strong>on</strong>juncti<strong>on</strong> with a cl<strong>in</strong>ical <strong>and</strong> public health risk assessment. If available,IGRA can be used for <strong>the</strong> diagnosis <strong>of</strong> LTBI <strong>in</strong> <strong>the</strong> follow<strong>in</strong>g sett<strong>in</strong>gs.C<strong>on</strong>tact trac<strong>in</strong>g (see chapter 8)• The TST (Mantoux test) should be used as <strong>the</strong> first l<strong>in</strong>e test for <strong>the</strong> diagnosis <strong>of</strong> LTBI <strong>in</strong> c<strong>on</strong>tacts<strong>of</strong> <strong>in</strong>fectious TB cases <strong>and</strong> o<strong>the</strong>rs c<strong>on</strong>sidered to be at high risk <strong>of</strong> LTBI. Those with positive TSTresults should be c<strong>on</strong>sidered for IGRA test<strong>in</strong>g, if available (see figures 8.1 & 8.2)• IGRA may be c<strong>on</strong>sidered <strong>on</strong> a case by case basis <strong>in</strong> adults <strong>and</strong> children as per <strong>the</strong> generalrecommendati<strong>on</strong>s <strong>in</strong> secti<strong>on</strong> 8.7. 60Pre-placement screen<strong>in</strong>g <strong>of</strong> HCWsIn new HCWs who are asymptomatic for TB <strong>and</strong> have a low pre-test probability <strong>of</strong> LTBI, IGRA, if available,can be used to c<strong>on</strong>firm a positive TST result. Pers<strong>on</strong>s with a positive IGRA should be c<strong>on</strong>sidered fortreatment <strong>of</strong> LTBI (see chapter 9).New entrant screen<strong>in</strong>gAlthough <strong>the</strong> use <strong>of</strong> IGRA <strong>in</strong> screen<strong>in</strong>g new entrants has not clearly been dem<strong>on</strong>strated to date, <strong>the</strong> use <strong>of</strong>IGRA can be c<strong>on</strong>sidered:• As a c<strong>on</strong>firmatory test <strong>in</strong> those <strong>in</strong>dividuals with a positive TST• In screen<strong>in</strong>g new entrants with c<strong>on</strong>comitant c<strong>on</strong>diti<strong>on</strong>s that <strong>in</strong>crease <strong>the</strong> <strong>in</strong>dividual’s risk <strong>of</strong>reactivati<strong>on</strong> <strong>of</strong> LTBI (chapter 9).For <strong>in</strong>dividuals commenc<strong>in</strong>g <strong>on</strong> immunosuppressive <strong>the</strong>rapy, i.e. tumour necrosis factor-α (TNF-α)antag<strong>on</strong>ists.• IGRA, if available, can be used as an adjunct to screen<strong>in</strong>g <strong>in</strong> additi<strong>on</strong> to a medical history, chestX-ray <strong>and</strong> TST.IGRA, if available, can be c<strong>on</strong>sidered as <strong>the</strong> sole test for LTBI <strong>in</strong> <strong>the</strong> situati<strong>on</strong> outl<strong>in</strong>ed below:• When screen<strong>in</strong>g large numbers <strong>of</strong> <strong>in</strong>dividuals as part <strong>of</strong> a public health <strong>in</strong>vestigati<strong>on</strong> where logisticissues make repeated visits for sequential test<strong>in</strong>g impractical. 54Recommendati<strong>on</strong>:For c<strong>on</strong>tact trac<strong>in</strong>g, <strong>the</strong> TST (Mantoux test) should be used as <strong>the</strong> first l<strong>in</strong>e test for <strong>the</strong>diagnosis <strong>of</strong> LTBI <strong>in</strong> c<strong>on</strong>tacts <strong>of</strong> <strong>in</strong>fectious TB cases <strong>and</strong> o<strong>the</strong>rs c<strong>on</strong>sidered to be at high risk <strong>of</strong>LTBI. Those with positive TST results should be c<strong>on</strong>sidered for IGRA test<strong>in</strong>g (see figures 8.1 &8.2). IGRA may be c<strong>on</strong>sidered <strong>on</strong> a case by case basis <strong>in</strong> adults <strong>and</strong> children as per <strong>the</strong> generalrecommendati<strong>on</strong>s <strong>in</strong> secti<strong>on</strong> 8.7. 60IGRA performance <strong>in</strong> immunocompromised populati<strong>on</strong>sThere are few studies <strong>on</strong> <strong>the</strong> sensitivity <strong>and</strong> specificity <strong>of</strong> IGRA <strong>in</strong> immunocompromised populati<strong>on</strong>s. TSTsensitivity is modest to poor <strong>in</strong> <strong>the</strong>se populati<strong>on</strong>s. The sensitivity <strong>of</strong> T-SPOT.TB appears to be ma<strong>in</strong>ta<strong>in</strong>ed<strong>in</strong> immunocompromised <strong>in</strong>dividuals <strong>and</strong> appears to have a higher rate <strong>of</strong> positivity than TST. QuantiFer<strong>on</strong>studies have not dem<strong>on</strong>strated this. 60 In <strong>the</strong> immunocompromised pers<strong>on</strong> (adult or child), <strong>the</strong> TST shouldbe <strong>the</strong> <strong>in</strong>itial test used to detect LTBI. If <strong>the</strong> TST is positive, <strong>the</strong> pers<strong>on</strong> should be c<strong>on</strong>sidered to have LTBI.However, <strong>in</strong> light <strong>of</strong> <strong>the</strong> known problem <strong>of</strong> false negative TST results <strong>in</strong> immunocompromised populati<strong>on</strong>s,a cl<strong>in</strong>ician still c<strong>on</strong>cerned about <strong>the</strong> possibility <strong>of</strong> LTBI <strong>in</strong> an immunocompromised pers<strong>on</strong> with an <strong>in</strong>itialnegative TST result may perform an IGRA test. If <strong>the</strong> IGRA test is positive, <strong>the</strong> pers<strong>on</strong> might be c<strong>on</strong>sideredto have LTBI. If <strong>the</strong> IGRA result is <strong>in</strong>determ<strong>in</strong>ate, <strong>the</strong> test should be repeated to rule out laboratory error.If <strong>the</strong> sec<strong>on</strong>d test is negative, <strong>the</strong> cl<strong>in</strong>ician should suspect anergy <strong>and</strong> rely <strong>on</strong> <strong>the</strong> pers<strong>on</strong>’s history, cl<strong>in</strong>ical-19-
<str<strong>on</strong>g>Guidel<strong>in</strong>es</str<strong>on</strong>g> <strong>on</strong> <strong>the</strong> Preventi<strong>on</strong> <strong>and</strong> C<strong>on</strong>trol <strong>of</strong> <strong>Tuberculosis</strong> <strong>in</strong> Irel<strong>and</strong> 2010HSE/HPSCfeatures <strong>and</strong> o<strong>the</strong>r laboratory results to make a decisi<strong>on</strong> <strong>on</strong> <strong>the</strong> likelihood <strong>of</strong> LTBI. Ei<strong>the</strong>r IGRA test may beused, however, <strong>the</strong>re is evidence that <strong>the</strong> T-SPOT.TB assay may be more sensitive that <strong>the</strong> QuantiFer<strong>on</strong> test<strong>and</strong> this will be especially relevant for immunocompromised populati<strong>on</strong>s. 60While <strong>the</strong> approach <strong>of</strong> accept<strong>in</strong>g ei<strong>the</strong>r test result (TST or IGRA) as positive will improve <strong>the</strong> sensitivity<strong>of</strong> detect<strong>in</strong>g LTBI <strong>in</strong> immunocompromised populati<strong>on</strong>s, <strong>the</strong>re are no data support<strong>in</strong>g <strong>the</strong> efficacy <strong>of</strong>preventive <strong>the</strong>rapy <strong>in</strong> TST negative but IGRA positive <strong>in</strong>dividuals. Thus <strong>the</strong> cl<strong>in</strong>ician must weigh <strong>the</strong>potential benefit <strong>of</strong> detect<strong>in</strong>g more pers<strong>on</strong>s with positive test results aga<strong>in</strong>st <strong>the</strong> lack <strong>of</strong> evidence for <strong>the</strong>benefit <strong>of</strong> preventive <strong>the</strong>rapy <strong>in</strong> such pers<strong>on</strong>s.Potential boost<strong>in</strong>g <strong>of</strong> IGRA by previous TSTPrevious guidel<strong>in</strong>es by CDC state that <strong>the</strong> results <strong>of</strong> IGRA are not <strong>in</strong>fluenced by previous TST. 51 Studiesby Leyten et al 66 <strong>and</strong> Richeldi et al 67 report no boost<strong>in</strong>g phenomen<strong>on</strong> follow<strong>in</strong>g <strong>the</strong> evaluati<strong>on</strong> <strong>of</strong> T-SPOT.TB assay. Some studies however, have reported boost<strong>in</strong>g <strong>of</strong> <strong>the</strong> QuantiFERON-TB Gold® In –Tube assayresults when taken 6 to 8 weeks after a TST. 68;69 Although <strong>the</strong>se studies have limitati<strong>on</strong>s, <strong>the</strong>re are animalstudies suggest<strong>in</strong>g that TST might boost subsequent measurements <strong>of</strong> <strong>in</strong>terfer<strong>on</strong> gamma. 70;71 This issuerequires fur<strong>the</strong>r <strong>in</strong>vestigati<strong>on</strong>. Due to <strong>the</strong>se c<strong>on</strong>cerns, it is recommended by both <strong>the</strong> HPA <strong>and</strong> <strong>the</strong> PublicHealth Agency <strong>of</strong> Canada that <strong>the</strong> IGRA test should be undertaken at <strong>the</strong> time <strong>of</strong> read<strong>in</strong>g <strong>the</strong> Mantouxresults. 54;60Serial test<strong>in</strong>gThere are <strong>in</strong>sufficient data to <strong>in</strong>form recommendati<strong>on</strong>s <strong>on</strong> serial test<strong>in</strong>g with IGRA. Studies <strong>of</strong> serial test<strong>in</strong>g<strong>of</strong> <strong>in</strong>dividuals with ei<strong>the</strong>r LTBI or TB disease do not show a clear pattern. In some studies, IGRA resp<strong>on</strong>ses<strong>in</strong>creased, 72 decreased 73 or showed no change. 74 Fur<strong>the</strong>r studies are needed.Diagnosis <strong>of</strong> active TB diseaseIGRA should not be used <strong>in</strong> <strong>the</strong> first <strong>in</strong>stance for <strong>the</strong> diagnosis <strong>of</strong> active TB disease <strong>in</strong> ei<strong>the</strong>r adults orchildren <strong>and</strong> should not replace <strong>the</strong> appropriate microbiological <strong>and</strong> molecular <strong>in</strong>vestigati<strong>on</strong>.Culture rema<strong>in</strong>s <strong>the</strong> gold st<strong>and</strong>ard for <strong>the</strong> diagnosis <strong>of</strong> TB disease as it provides a def<strong>in</strong>itive diagnosis <strong>and</strong>permits <strong>the</strong> identificati<strong>on</strong> <strong>of</strong> drug resistance. IGRA have no benefits <strong>in</strong> known pulm<strong>on</strong>ary TB cases withbacteriological/molecular c<strong>on</strong>firmati<strong>on</strong>.Recommendati<strong>on</strong>:IGRA tests should not be used <strong>in</strong> <strong>the</strong> first <strong>in</strong>stance for <strong>the</strong> diagnosis <strong>of</strong> active TB disease.Appropriate microbiological <strong>and</strong> molecular <strong>in</strong>vestigati<strong>on</strong>s rema<strong>in</strong> <strong>the</strong> gold st<strong>and</strong>ard.However, <strong>in</strong> some patients (adults <strong>and</strong> children) with TB, it is not possible to isolate M. tuberculosis fromcl<strong>in</strong>ical specimens or to obta<strong>in</strong> cl<strong>in</strong>ical specimens, despite <strong>the</strong> <strong>in</strong>dividual hav<strong>in</strong>g symptoms, signs <strong>and</strong>/or radiological changes c<strong>on</strong>sistent with <strong>the</strong> diagnosis <strong>of</strong> TB. In <strong>the</strong>se circumstances, a positive IGRA may<strong>in</strong>crease c<strong>on</strong>fidence <strong>in</strong> <strong>the</strong> diagnosis. In those with symptoms or signs compatible with but not <strong>in</strong>dicative<strong>of</strong> <strong>the</strong> diagnosis <strong>of</strong> TB, a positive IGRA test may suggest more str<strong>on</strong>gly <strong>the</strong> possibility <strong>of</strong> a TB diagnosis. 54However, <strong>the</strong> f<strong>in</strong>al decisi<strong>on</strong> should be based <strong>on</strong> cl<strong>in</strong>ical judgment. 54 60 IGRA tests cannot dist<strong>in</strong>guishbetween active TB <strong>and</strong> LTBI. 60Advantages <strong>of</strong> IGRA tests• It <strong>on</strong>ly requires <strong>on</strong>e visit from <strong>the</strong> patient compared to two visits for a TST• IGRA dem<strong>on</strong>strate improved specificity over <strong>the</strong> TST i.e. <strong>the</strong> proporti<strong>on</strong> identified as disease free<strong>and</strong> <strong>the</strong> reduced cross-reactivity with BCG vacc<strong>in</strong>e <strong>and</strong> most NTM means that pers<strong>on</strong>s are less-20-
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