Quantiferon-Gold implementation: Beth Israel Deaconess Medical Center/MA State TB Lab collaboration

1
IGRAs for Diagnosis of Tuberculosis 2010
Update
Nira Pollock, M.D., Ph.D. Division of Infectious
Diseases Beth Israel Deaconess Medical
Center Boston, MA May 1, 2010
2
Problems with the PPD

• False positives
• Recent BCG vaccine
• non-TB mycobacteria (NTM)
• False negatives
• 25-30 patients with active pulmonary TB
  initially negative
• Newborn/elderly, immunosuppression, renal
  failure, acute non-TB infection, etc
• unable to distinguish active disease from past
  exposure

3
Interferon-gamma Release Assays (IGRAs) basic
concepts

• Expose T cells (isolated, or within whole blood)
  to
• TB antigens (in peptide form), vs
• positive control antigen (mitogen, e.g.
  phytohemagglutinin A), vs
• negative control (e.g. saline)
• Incubate overnight
• T cells (both CD8 and CD4) previously sensitized
  to these TB antigens in vivo release IFN-?
• Mitogen stimulates cells non-specifically to
  release IFN-?? as control for general T-cell
  anergy
• Saline control defines level of background
  (should be low)
• Quantify amount of IFN-??produced under each
  condition

4
IGRAs basic concepts, cont.

• Theory overnight incubation detects sensitized
  effector T cells, i.e. already activated in
  vivo (longer incubation could activate resting
  central memory T cells also)
• ? Primarily CD4 (Mack et al, 2009)
• Like PPD, IGRAs are unable to distinguish between
  LTBI and active disease

Mack et al, TBNET consensus statement Eur Respir
J 2009
5
Quantiferon-TB-Gold (Cellestis,
Inc.)FDA-approved May 2005 for detection of LTBI
and TB disease
must incubate cells with antigen within 12
hours of collection
6
Quantiferon-TB Gold

• Peptide antigens used in assay simulate two
  proteins specific to Mycobacterium tuberculosis
  complex (MTBC M. tuberculosis, M. bovis, M.
  africanum, M. microti, M. canettii)
• ESAT-6, CFP-10 (genes coding for both are found
  within MTBC RD1 region, which is deleted in M.
  bovis BCG strain)
• Eliminates false-positives due to BCG vaccination
  and to almost all NTM (exceptions M.
  kansasii, M. marinum, M. szulgai)

7
3rd generation QFT-Gold In Tube (IT)

• FDA-approved October 2007
• NOW FORMALLY REPLACING 2nd GENERATIONcompany no
  longer making prior version!
• Specimen collection draw whole blood directly
  into three proprietary 1 mL blood collection
  tubes
• 1) TB-specific Ag (dried onto wall of tube)
• 2) Nil (-) control
• 3) Mitogen () control (dried onto wall of tube).
  
• TB-specific peptide antigens ESAT-6, CFP-10,
  TB7.7. Goal of adding extra antigen increase
  sensitivity. (Like ESAT-6/CFP-10, TB 7.7 is not
  present in BCG strains and most NTM.)

8
QFT-Gold IT (continued)

• Must not under or over-fill tube. Shake 10x
  vigorously after draw. Keep at room temp.
• Must put at 37ºC within 16h of collection.
• Incubate upright at 37ºC for 16-24h
• Tubes can then be held at 2-27ºC for up to 3 days
  prior to centrifugation (so can ship at room
  temp).
• Centrifuge 15 to separate plasma from cells,
  remove gt150 ?L plasma to assay (can store spun
  tube or plasma at 4ºC for 28 days).
• Quantify IFN-? in plasma by ELISA, as for QFT-G
• IT test format allows o/n incubation at site of
  draw (e.g. hospital or clinic), vs central
  testing center
• QFT-G IT is being done at the Hinton State Lab
  (contact them to obtain tubes and arrange
  submission) also offered at e.g. Quest

9
(No Transcript)
10
QFT-G IT, continued

• Quantification of IFN-? ELISA, as for QFT-G
• Results readout positive, negative, or
  indeterminate
• Ideally, lab should report absolute value result
  in IU/mL, so that clinician can evaluate how
  close absolute value is to the cutoff
• Lab should also report reason for indeterminate
• Low mitogen response insufficient or
  dysfunctional lymphocytes, reduced lymphocyte
  activity due to prolonged specimen transport,
  improper specimen handling
• High background in nil control heterophile
  antibodies (interfering human anti-mouse
  antibodies), intrinsic IFN-gamma secretion (?
  recent vaccination, ? just true for some
  people--1-2 of population per Cellestis website)

11
QFT-G IT results interpretation
Note for QFT-G this value was gt50 seems that
new cutoff would generate more positives
Note for QFT-G nil cutoff was 0.7 IU/mL seems
that new cutoff of 8.0 would generate a lot fewer
indeterminates..
12
T-Spot.TB (Oxford Immunotec Elispot
technology)FDA-approved July 2008

• in vitro diagnostic test based on an
  enzyme-linked immunospot (ELISPOT) method
• enumerates M.tuberculosis-sensitized effector T
  cells responding to stimulation with a
  combination of peptides simulating ESAT-6 and
  CFP10 antigens, by capturing interferon-gamma
  (IFN-?) in the vicinity of T cells from which it
  was secreted

13
T-Spot.TB
Each spotone reactive effector T-cell
14
TSpot.TB results interpretation

• Positive (ESAT-6-Nil) and/or (CFP-10-Nil) are gt
  8 spots.
• (note this cutoff used to be 6 spots)
• Negative both (ESAT-6-Nil) and (CFP-10-Nil) are
  lt 4 spots.
• (includes values less than zero).
• Borderline (equivocal) highest (TB antigen-Nil)
  spot count is 5, 6 or 7 spots
• Collect a new specimen and retest
• Indeterminate
• nil control count is gt10 spots, OR
• mitogen control count is lt20 spots and (TB
  Ag-nil) counts are lt4 spots

15
Doing T-Spot in MA

• Oxford Immunotec has a testing facility in
  Marlborough (since July 2009) CLIA/CAP
  certified
• Specimens (blood only) must be shipped at room
  temp day of draw and have 32 hours to reach
  testing center (package insert says 8 hours, but
  Oxford has validated longer time frame) contact
  Oxford for details (tubes, shipping)

16
Assessing the accuracy of IGRAs

• General principles used to date
• Sensitivity approximated by measuring
  proportion of positive tests in patients with
  culture-confirmed active TB
• Specificity approximated by measuring proportion
  of negative tests in patients with low risk for
  TB infection
• Problem no confirmatory test exists for
  diagnosis of LTBI or culture-negative TB disease
  (no gold standard!)

17
QFT-G IT package insert (Jan 2009)

• Sensitivity in culture-confirmed active TB (all
  with lt8days treatment prior to testing)
• Japanese study (n92) QFT-G IT 93.5, QFT-G
  83.7
• Australian study (n27) QFT-G IT 88.9, QFT-G
  74.1
• US study (n44) QFT-G IT 84.1, QFT-G 77.3
• Overall sensitivity QFT-G IT 89, QFT-G 81
• Specificity in subjects at low reported risk for
  TB infection (US study subjects had no reported
  TB risk factors, and none had BCG history)
• Overall specificity QFT-G IT 99.2, QFT-G
  99.8, TST 99.1

18
QFT-G IT package insert (Jan 2009)

• Cautions that the performance of the USA format
  of QFT-G IT has not been extensively evaluated
  in
• Individuals who have impaired or altered immune
  function such as HIV infection/AIDS, s/p
  transplantation managed with immunosuppressive
  treatment, patients on immunosuppressive drugs
  (e.g. corticosteroids, methotrexate,
  azathioprine, cancer chemotherapy)
• Patients with the following clinical conditions
  diabetes, silicosis, chronic renal failure,
  hematological disorders (e.g., leukemia and
  lymphomas), and other specific malignancies
  (e.g., carcinoma of the head or neck and lung).
• Individuals younger than age 17 years
• Pregnant women

19
Review of TSpot.TB FDA approval document/PI (July
2008)

• Sensitivity in culture-confirmed active disease
  (n183)
• 95.6 using gt6 spots, 90.7 using gt8
  spots.
• Specificity (used individuals with no TB risk
  factors and negative TST) (n306)
• 97.1 using gt6 spots, 99.0 using gt8 spots
  (i.e. if equivocal (5,6, or 7 spots) are
  counted as negative).
• Equivocal or borderline result (TB Ag-nil
  5,6, or 7 spots) represents the area of overlap
  between results obtained for culture-confirmed
  positive samples and low risk TB negative samples
• Note Oxford Immunotec website (4/12/10) quotes
  95.6 sensitivity and 97.1 specificity, but
  these are for gt6 spot cutoff, whereas current
  version uses gt8 spot cutoff and equivocal range.

20
TSpot.TB FDA approval/PI (July 2008) clinical
studies

• Goal include subjects from all major risk
  groups indicated for TB screening by CDC
  guidelines (including those with potential for
  false positive/negative TST)
• TSpot.TB vs TST evaluated in typical candidates
  for routine LTBI screening, with various risk of
  exposure and progression (n1403) (NOTE used gt6
  spot cutoff)
• Included 328 HIV, 229 recent contacts, 122
  drug-induced immunosuppression, 97 IVDU, 108 DM,
  195 ESRD. Many BCG-vaccinated and foreign-born.
  93 children/adolescents.

21
TSpot.TB FDA approval/PI clinical
studiesaggregate results (not by clinical
subgroup)

• After controlling for the other variables,
  positive results for both T-SPOT.TB and TST were
  significantly associated with history of prior TB
  infection.
• A positive result for T-SPOT.TB was significantly
  associated with contact with infectious TB and
  birth in a TB endemic country no such
  association observed for TST.
• A positive TST was associated with BCG
  vaccination no such association observed for
  T-SPOT.TB
• A negative TST was associated with being
  immunocompromised no such association observed
  for T-SPOT.TB
• TSPOT.TB results were not impacted by age

22
TSpot.TB FDA approval document/PI (continued)

• Notes theoretical cross-reaction (false-positive
  test) with M. kansasii, M.szulgai, M. marinum, M.
  xenopi, M gordonae (latter two not mentioned in
  QFT-G IT PI). However, actual data obtained in a
  very small of patients12 with MAC (all
  negative with TSpot), 1 with xenopi (positive), 4
  with gordonae (all positive), 1 with kansasii
  (positive). (note no marinum..)
• The performance of this test has not been
  adequately evaluated with specimens from
  individuals younger than age 17 years, in
  pregnant women and in patients with hemophilia

23
Direct comparisons of QFT-G IT, TSpot.TB, and
TST meta-analysis

• Diel et al, Chest 2010
• Evaluated comparative sensitivity in studies of
  subjects with active TB confirmed by culture
  and/or PCR and/or histologic evaluation, treated
  for lt2 weeks
• Evaluated comparative specificity for LTBI in
  studies of subjects who were healthy, native
  residents of low-incidence countries without any
  previously known exposure to TB, irrespective of
  BCG vaccination status.
• Evaluated indeterminate rates (though no apparent
  distinction between indeterminates due to high
  background, vs low mitogen)
• Included studies that evaluated immunosuppressed
  subjects
• Note cutoff for TSpot.TB was gt6 spots in all
  included studies, which as discussed is different
  than FDA-approved version

24
Diel et al metaanalysis, cont

• Pooled sensitivities in active TB
• TST 69.9
• QFT-G IT 81.
• Note that in studies done in developing
  countries, sensitivity was 74.3, vs 84.5 in
  developed countries. (Is this difference due to
  HIV co-infection, malnutrition, or other
  factors?)
• TSpot.TB 87.5.
• Majority of studies done in developed countries
  sensitivity in that subgroup was 88.5
• Pooled specificities in low-risk subjects
• QFT-G IT (5 studies) 99.2
• TSpot.TB (3 studies) 86.3
• Pooled rates of Indeterminates
• QFT-G IT 2.1. In immunosuppressed subgroup
  4.4
• TSpot.TB 3.8. In immunosuppressed subgroup
  6.1

25
IGRA performance in specific groups of interest
26
e.g. contacts of active TB cases

• Overall consensus, IUATLD NAR meeting, Vancouver,
  2007 overall both IGRAs performing well (and
  comparably) in contact investigations
• Tspot.TB and QFT-G (including IT version) results
  correlate better than TST results with exposure
  to MTB1, 2
• Direct comparison TSpot.TB vs QFT-IT vs TST,
  20093 both IGRAs appeared to indicate LTBI more
  accurately than TST, and IGRAs agreed well
• Suggests that IGRAs may be as or more sensitive
  than TST for recently acquired infection (in
  immunocompetent)

(1 Richeldi, AJRCCM 2006 2 Arend et al, AJRCCM
2007 3 Diel et al, Chest 2009)
27
e.g. HIV Data mixed can use IGRAs, but watch
for indeterminates, particularly at low CD4

• QFT-G IT e.g. Brock et al, 2006, Denmark
  indeterminates correlated with low CD4 (24 in
  pts with CD4lt100).
• ELISPOT assays1 overall perform better than TST.
  E.g. Dheda et al, 2005 T-Spot.TB in
  HIV-positive pts w/o other TB risk factors
  technical performance independent of CD4 count.
  However, another study found more indeterminates
  with Tspot vs QFT-G (Stephan et al, 2008)
• Tspot may be more sensitive than QFT-G in this
  population (Mandalakas et al, 2008, small study
  in S. African patients)

1Kimura et al 1999 Chapman et al, 2002 Carrara
et al, 2004, Dheda et al 2005
28
HIV, continued

• Diagnosis of active TB in HIV
• QFT-G IT might be a sensitive tool for
  detection/prediction of active TB in HIV
  (Aichelburg et al, CID 2009), or NOT (Aabye et
  al, PLoSONE 2009)
• Cattamanchi et al, BMC ID 2010 TSpot.TB in 236
  HIV active TB suspects in Uganda mean CD4 of
  49. 126 patients diagnosed with active TB by
  culture. 10 of subjects had insufficient
  mononuclear cell counts for TSpot assay. Of
  remainder
• 25 had indeterminate results
• IGRA sensitivity was 73
• Proportion of positive test results was similar
  across CD4 count strata
• IGRA results did not meaningfully alter the
  probability of active TB in patients with
  negative sputum smears
• If IGRA sensitivity might be lower in HIV
  subjects (vs immunocompetent) with active TB
  (recall also Diel metaanalysis), what does this
  mean re sensitivity for LTBI?

29
Immunocompromised patients

• IGRAs (vs TST) do allow optimization of
  experimental conditions in vitro, e.g. incubation
  time or adjustment of cell numbers, allowing
  potential for higher sensitivity. However,
  studies are as usual limited by lack of gold
  standard for LTBI.
• Overall IGRAs seem to work, but true sensitivity
  for LTBI unknown.
• In earlier studies, QFT-G had higher rate of
  indeterminates (low mitogen control) than
  TSpot.TB (Ferrara et al, AJRCCM 2005 (Italy)
  Piana et al, AJRCCM 2006 (Italy) Ferrara et al,
  Lancet 2006 (Italy))
• More recent metaanalysis (Diel et al, 2010)
  rates of indeterminates (note reason for
  indeterminate not defined) in immunosuppressed
  subgroups
• QFT-G IT 4.4
• TSpot.TB 6.1
• Occasional case reports of IGRAs being used to
  help with Dx of active TB in TST-negative
  immunosuppressed patients
• Disturbing case report of person who was QFT-G
  negative before liver transplant AND in setting
  of post-transplant active (Cx-positive) pulmonary
  TB (Codeluppi et al, 2006)

30
e.g. health care workers (HCW) depends where you
are and what question you ask. For example

• Japan (Harada, 2006) QFT-G vs TST
• 95 s/p BCG. 93 TSTgt10mm, vs 10 QFT-G.
  QFT-G results were a/w LTBI risk factors, while
  TST results were not.
• Rural India (Pai, 2005) QFT-IT vs TST
• 50 positive by either test, 31 by both
• Russia (Drobniewski, 2007) QFT-IT
• QFT-IT was positive in 8.7 of medical/non-medical
  students, 39.1 of all doctors/nurses, 46.9 of
  TB doctors and nurses
• Denmark (Soberg, 2007) QFT-G vs TST
• ID dept employees 34 TST, 1 QFT-G. 89 of
  TST were BCG-vaccinated.
• Urban US (Pollock, 2008) QFT-G
• In TST newly hired employees with increased risk
  of having LTBI (large PPD, residence in highly
  endemic area, recent or remote contact,
  conversion, CXR findings c/w old TB, patient
  care) 28 QFT-G, 70 QFT-G-
• Many more.mostly descriptive (TST results vs
  IGRA results)

31
Patients approaching TNF-alpha blocker therapy

• The problem many have underlying diseases or
  are on immunosuppressive medications which can
  compromise TST sensitivity. But how sensitive
  are the IGRAs in this group? Again, limited by
  lack of a gold standard.
• E.g. Laffitte et al, Br J Dermatol 2009
  retrospective study of TST vs T-Spot.TB in 50
  patients with psoriasis considering TNF-alpha
  blocker (in Switzerland)
• Positive TSpot was strongly a/w presumptive Dx of
  LTBI (by risk factors), while TST was not
• 20 of subjects had positive TST and negative
  TSpot and were NOT treated for LTBI no
  reactivation detected with median f/u of 64 weeks
  (but note, small numbers overall)
• E.g. Diel et al, Pneumologie 2009 (German
  recommendations) due to expectation of false
  negative AND false positive TST in these
  patients, they recommend highly specific IGRA
  instead (but what about IGRA sensitivity??)

32
Children

• Lewinsohn, Lobato, and Jereb, Curr Opin
  Pediatrics 2010
• Overall, performance of IGRAs equivalent or
  superior to that of the TST, but evidence
  supports usage of IGRAs in children aged 5 years
  or older only (insufficient evidence re
  performance in younger kids, and sensitivity
  poorly defined in that group)
• In kids gt5, IGRAs preferred over TST when
  specificity is paramount or when patients might
  not return for TST reading
• Kids lt5 TST preferred
• E.g. Bianchi et al, Pediatr Infect Dis J 2009
• QFT-G IT was positive in 15 of 16 (93.8)
  children with active pulmonary TB
• Among IGRA children (excluding active TB), TST-
  were significantly younger than TST children (so
  could IGRA be more sensitive than TST in younger
  kids?)

33
Are CFP-10, ESAT-6, /- TB7.7 sufficient for
comprehensive detection of LTBI?

• Overall in contact investigations, sensitivity
  of IGRATST, and IGRAs correlate better with TB
  exposure
• For active TB, sensitivity of IGRAs or gt to TST
• Could IGRAs be sensitive to recent/active
  infection, but not remote infection? (Pollock et
  al, ICHE 2008)

34
Relying on IGRAs for making clinical decisions
how much caution should we use at this point?

• if we base Tx decisions on IGRA results alone,
  many individuals with clinical risk factors
  historically considered suggestive of true LTBI
  will suddenly be exempt from treatment. Is this
  good or bad?
• AND, some of these risk factors have historically
  been associated with increased reactivation risk
  (e.g. PPDgt15 mm, recent immigration from high
  risk country, various CXR findings)
• But can IGRAs actually distinguish those at
  higher reactivation risk? Should we only care
  about the IGRA?

35
Studies of predictive value of IGRAs

• Hard to do studies of predictive value of
  positive IGRA for development of active
  TBtypically, ethically would need to consider
  treatment of LTBI if IGRA.
• E.g. Diel et al, AJRCCM 2008, Germany evaluated
  rates of progression to active TB in close
  contacts (immunocompetent) within 2 years of
  contact screening.
• 11 of contacts were QFT-G IT, vs 40 TST (gt5
  mm).
• 41 QFT-G IT subjects refused LTBI treatment 6
  (14.6) developed active TB. 219 TST subjects
  refused treatment 5 (2.3) progressed to active
  TB. Concluded that QFT-G IT is a more accurate
  indicator of LTBI than the TST and provides at
  least the same sensitivity for detecting those
  who will progress to active TB.
• Vs. e.g. Kik et al, Eur Respir J 2009 looked at
  immigrants who were close contacts of smear TB
  cases, all found to have TST gt5 mm during contact
  investigation followed for 2 years.
• PPV for progression to TB disease was comparable
  and LOW for QFT-G IT (2.8), T-Spot TB (3.3),
  TSTgt10 mm (3.1), TST gt15 mm (3.8)

36
Predictive value of IGRAs, cont

• E.g. Hill et al, PLoS One 2008, The Gambia risk
  of progression to active TB after positive
  ELISPOT (similar to TSpot) or TST in case
  contacts, over 2 year period. Noone got
  preventive therapy, per local guidelines.
• Rates of progression in ELISPOT was similar to
  rates in TST.
• Because initial ELISPOT and TST were each
  positive in just over half of secondary cases,
  while 71 were initially positive by one or the
  other test, they concluded that positivity by
  either might be the best indication for
  preventive treatment.
• Note there were clearly some NEW infections over
  study time period (discordant genotyping between
  index and secondary case isolates) so this really
  confuses this study.
• San Francisco IGRA experience--?? Not seeing
  spike in TB cases after switching to IGRA only
  for TB screening programs..

37
Our clinical response to all this data We feel
great about the IGRA. Were just not sure what
to do with all the IGRA-

• We dont assume (for now) that a negative IGRA
  rules out LTBI. Perhaps, in future, we can be
  confident that it doesor, at least, that it
  rules out high baseline reactivation risk.
• Consider offering treatment to certain high-risk
  populations even with a negative IGRA result
• 1. Patients with medical risk factors placing
  them at higher risk of TB reactivation if they do
  have LTBI, i.e. HIV, chronic oral steroid
  treatment, TNF-alpha blocker treatment, renal
  insufficiency, diabetes, some malignancies.
• 2. recent TB contact (debatable, given good IGRA
  performance in contact studies)
• 3. PPD conversion (gt10 mm increase) in past 2
  years (also debatable, given performance in
  contact studies)
• 3. Abnormal CXR potentially consistent with old
  TB in significant burden (e.g. large scar,
  nodule, after r/o with smear/culture)

38
FAQ Do positive IGRA results turn negative with
TB or LTBI treatment?

• Multiple studies on this topic data mixed, but
  general consensus is NO, not reliably.
• E.g. local study Pollock et al, ICHE 2009 HCW
  treated for LTBI with 9 months INH still had
  positive QFT-G after treatment.
• Suggested approach to this issue based on current
  data
• IGRA results should not be used to assess the
  effectiveness of recent or remote treatment
  courses for TB/LTBI many (if not most)
  individuals will continue to test positive after
  standard therapy
• Do not assume that an individual who reports
  prior TB/LTBI therapy but still tests positive by
  IGRA has not been appropriately treated in the
  past
• Neither providers nor patients should expect
  reliable changes in IGRA results after standard
  treatment

39
Serial testing with IGRAs

• Primarily relevant to HCW or other individuals
  requiring annual screening
• Multiple issues to think about
• reproducibility of test results in a given
  individual tested repeatedly over time, without
  intervening exposures to TB
• appropriate definition of reversion/conversion
• optimal test cutoffs
• (e.g. initially raised by Pai et al, 2006,2009,
  India)

40
From QFT-G IT package insert

• The magnitude of the measured IFN-g level cannot
  be correlated to stage or degree of infection,
  level of immune responsiveness, or likelihood for
  progression to active disease.

41
Reproducibility of IGRA results in serial testing

• E.g. Detjen et al, Clin Vaccine Immunol 2009 27
  S. African HCW, tested with QFT-G IT on day 1 (2
  tests, by different operators) and day 3 (1
  test).
• 6/27 had discordant results of some kind
• variability in the magnitude of IFN-gamma
  responses between assays performed for a given
  individual
• most variability seen in assays that were
  obtained from an individual on two different
  days.
• Conclusion This intra-individual variability
  could influence interpretation of serial
  measurements
• E.g. Van Zyl-Smit, AJRCCM 2009 26 S. African
  subjects repeated IGRAs (T.SpotTB, QFT-G IT) 4x
  over 21D prior to TST (to assess within-patient
  variability), and then again on days 3,7,28, 84
  post-TST (to assess for boosting of IGRA by TST).
• Pre-TST tests 7/26 had spontaneous
  conversions/reversions (6 for TSpot, 1 for QFT-G
  IT). 95 of variability was 3-spot or 80
  IFN-gamma response variation on either side of
  baseline valuescould be useful for interpreting
  conversions/reversions

42
Effect of TST on IGRA results

• QFT-G IT package insert in U.S. specificity
  study (individuals with no reported TB risk
  factors), a subset of subjects were retested 4-5
  weeks after initial QFT-G IT/TST. Agreement
  between 2 QFT-G IT tests was 98.5 (out of 530
  subjects, 5 went pos?neg, and 3 went neg?pos.)
• Van Zyl-Smit, AJRCCM 2009 26 S. African
  subjects after baseline IGRAs (T.SpotTB, QFT-G
  IT), repeated IGRAs on days 3,7,28, 84 post-TST
  (to assess for boosting of IGRA by TST).
• Post-TST tests 8 subjects boosted above
  defined baseline variability by day 7, but not
  day 3. 2 initially IGRA-negative subjects
  converted to IGRA-positive.
• Conclusion safe to do QFT-G IT or TSpot within
  3 days of performing TST (i.e. on day of TST
  read).
• Cohort as a whole showed some persistently
  elevated IFN-gamma responses up to day 84 after
  TST, though some individuals had returned to pre-
  TST levels by day 28.(So what are implications
  for long-term boosting effects, e.g. in those
  receiving annual testing?)

43
Effect of TST on IGRA, continued

• Review by van Zyl-Smit et al, PLoSOne 2009 13
  studies
• Studies used different TU for TST, different time
  points for IGRAs after TST, and varied re
  initial TST/IGRA status of individuals
• 5 studies concluded boosting of IGRA by TST did
  NOT occur in 4/5, earliest timepoint of repeat
  IGRA was 28 days-9 months after TST. In 5th,
  IGRA was repeated only on day 3 after TST.
• 7 studies demonstrated TST-induced boosting
  of IGRA responses in 5/7, repeat IGRA was done
  within 21 days after TST.
• Conclusions
• Boosting more pronounced in IGRA-positive (i.e.
  sensitized) individuals, but also occurred in a
  smaller but not insignificant proportion of
  IGRA-negative subjects
• Time frame of repeat IGRA is key. TST appeared
  to affect IGRA responses only after 3 days, and
  may be issue particularly between days 7-28
  boosting effect may apparently persist for up to
  3 months and then wane, but evidence for this is
  weak.

44
Preliminary (unpublished) data from a 4-site
(U.S.) collaborative study of serial IGRAs in HCW

• Longitudinal study of HCW undergoing routine
  testing for LTBI overall low risk for TB
  acquisition at work
• 15 born in high-burden country
• 10 s/p BCG
• 0.4 HIV, 3 DM, 2 other immunocompromise
• Baseline 2-step TST, QFT-G IT, TSpot.TB
• IGRAs done BEFORE placement of 1st TST
• Repeat all 3 tests at 6, 12, and 18 months

Slides obtained from Dr. John Bernardo, BMC
45
Baseline Results in subjects with no prior ()
TST or LTBI treatmentn 2083
TST QFT T-SPOT
Positive 43 (2.1) 76 (3.7) 108 (5.2)
Negative 2040 (97.9) 2007 (96.3) 1907 (91.6)
Borderline 68 (3.3)
p lt 0.0001 compared to the TST (borderline
T-Spots categorized as negative)
46
6 month Follow-up
Conversion Reversion
TST 6 / 1503 (0.4) 11 / 21 (52.4)
QFT-GIT 56 / 1516 (3.7) 28 / 56 (50)
T-SPOT 52 / 1473 (3.3) 47 / 85 (55.3)
Conversion (-) baseline () 6 month Reversion
() baseline (-) 6month
Total Baseline Positive 43 TST, 76 QFT-GIT,
108 T-SPOT
47
12 month Follow-up
Conversion Reversion
TST 1 / 362 (0.3) n/a
QFT-GIT 9 / 384 (2.3) 7 / 11 (63.6)
T-SPOT 3 / 356 (0.8) 10 / 16 (62.5)
Conversion (-) baseline (-) 6 month () 12
month Reversion (-) baseline () 6month (-)
12 month
48
Some take-home points

• IGRAs should not be used alone to exclude the Dx
  of active TB
• In particular, sensitivity in question for
  extra-pulmonary TB1
• IGRAs cannot distinguish between active and
  latent TB
• IGRAs may remain positive even after appropriate
  treatment of active or latent TB.
• Sensitivity for diagnosis of LTBI is impossible
  to calculate, given absence of a gold standard
  for this Dx. Exercise caution when interpreting
  negative IGRA results in individuals with major
  risks for TB reactivation.
• A negative result must be considered with the
  individuals medical and historical data relevant
  to probability of M. tuberculosis infection and
  potential risk of progression to tuberculosis
  disease, particularly for individuals with
  impaired immune function. (QFT-G IT package
  insert, 2009)

1. Dewan et al, CID 2007
49
Some take-home points, cont.

• Specificity of IGRAs is very high, but
  occasionally you will see a patient with NO
  apparent TB risk factors and a positive IGRA
  result.
• Check absolute value to see if they are close to
  cutoff for positive
• would repeat, if negative repeat again as
  tie-breaker..
• Again, consider who should be tested in the first
  place, and who shouldnt
• It is still not clear how well IGRAs will perform
  in serial testing situations (e.g. HCW) or what
  the true impact of TSTs on subsequent IGRAs
  actually is. Can we trust conversions if IGRAs
  are used for annual testing in relatively low
  risk settings? Would those conversions be
  stable if we waited 6 months and retested?

50
December, 2005 CDC guidelines for use of QFT-G

• CDC recommends that QFT-G may be used in all
  circumstances in which the TST is currently used,
  including contact investigations, evaluation of
  recent immigrants, and sequential-testing
  surveillance programs for infection control
  (e.g., those for health-care workers).
• left open the possibility that "QFT-G sensitivity
  for LTBI might be less than that of the TST,"
  while acknowledging that the lack of a
  confirmatory test would make this difficult to
  assess
• "each QFT-G result and its interpretation should
  be considered in conjunction with other
  epidemiologic, historic, physical, and diagnostic
  findings."

51
New CDC recs for use of IGRAs in
developmentcoming in 2010!!??

• Likely to advocate broad use (including in annual
  testing), and use in place of TST, rather than as
  confirmatory test.
• My opinion if we are going to make clinical
  decisions based on IGRA results, then we need to
  focus on estimating IGRA sensitivity/NPV for LTBI
  and also potentially revisit the clinical
  guidelines regarding increased reactivation risk.
  What will we do with TST/IGRA- individuals who
• Have various forms of relative immunocompromise,
  or are going to become immunocompromised (e.g. by
  transplant, TNF-alpha blockers)?
• Are recent immigrants from endemic areas?
• Have CXR findings consistent with past TB (and
  which CXR findings, specifically, matter?)

52
MACET recommendations on use of IGRAs 6-13-08

• Recent contacts IGRAs seem to perform well
  (good sensitivity and correlation with TB
  exposure) can use IGRA or TST
• Immunocompromised two groups
• Pre-immunocompromisation (awaiting transplant,
  going on TNF-alpha blocker or steroids, etc)
  use both tests, Tx if either positive
• Already immunocompromised (including HIV) same
  recommendations

53
MACET recs 2008, cont.

• Recent immigrants panel unable to reach
  consensus, as negative test does not appear to
  rule out LTBI, and some of this population could
  be recently infected. Clinical f/u after testing
  is optimal.
• HCW same caveats as above. Agreed that either
  IGRA or TST could be used. Those with key
  reactivation risk factors who are IGRA negative
  should have clinical f/u if possible.

54
MACET recs 2008, continued

• Children limited data, no recommendations
  (could update, given recent analyses suggesting
  good performance in kidsgt5)
• Low-risk individuals given low pre-test
  probability, test results difficult to interpret.
  Best to NOT test with either IGRA or TST.
• Adults with recent BCG IGRAs can be helpful
  given high specificity
• Active TB can use IGRA to rule IN infection
  (either latent or active), but NOT to rule OUT
  active disease (given limits to sensitivity)