pasado y presente en el diagnóstico de la infección ......pasado y presente en el diagnóstico de...
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Pasado y presente en el diagnóstico de
la infección tuberculosa latente
J. DomínguezServei Microbiologia. Institut d’Investigació Germans Trias i Pujol
Badalona, Barcelona. ([email protected])
XVI Taller Internacional sobre Tuberculosis
UITB-2012
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LTBI diagnosis: Tuberculin skin test
o TST has been until now the only tool available for the diagnosis of
LTBI and is commonly used as complementary test for diagnosis of
active TB.
o Intradermal reaction test.
o TST attempts to measure cell-mediated immunity in the form of a
delayed-type hypersensitivity response to PPD.
o PPD contains more than 200 antigens that are widely shared among
mycobacteria other than M. tuberculosis, including the vaccinal strain
of Mycobacterium bovis BCG and many NTM.
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o 4th August 1890. R. Koch. X International Medicine Congress. Berlin
o 15th November 1890. German Medicine Journal.
o Between 1890-1891 doubtful curative effect.
o January 1891. Description of the substance production (Koch lymph,
Koch fluid, Bacillinum, Kochin).
o February 1891. The label of the product was: Tuberculin
o 1906 C. Von Pirquet demonstrated that the reactivity of the tuberculin
evidenced a previous contact with the bacteria
o Classical studies using tuberculin has allow to establish ratio of
infected individuals, and also the % of patients who developed active
TB at some time during their life.
Tuberculin origin
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LTBI diagnosis: Tuberculin skin testMain drawbacks
Low specificity
o Individuals sensitised by previous exposure to NTM or vaccinatedwith BCG respond immunologically to PPD.
Low sensitivity
o Low sensitivity in detecting LTBI in individuals with a high risk ofprogression to active TB: immunosuppressed patients (especiallywith deficient cellular immunity) and young children.
Logistical problems
o Errors in the administration and subjective reading of the results.
o Second reading visit. Some patients do not return to the readingof the TST result.
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LTBI diagnosis: IFN-γ releasedassays (IGRAs)
In vitro detection of IFN-γ released by sensitised T cells afterspecific M. tuberculosis antigens stimulation.
P. Andersen. Lancet 2000
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Moving LTBI diagnosis from clinical departments to laboratory.
A more accurate diagnosis.
LTBI diagnosis
2002
Tuberculin skin testing IGRAs
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LTBI diagnosis: IFN-γ assaysSpecific antigens
ESAT-6, CFP-10 and TB7.7
Proteins coded in the region of difference 1 and 11, which are
present in M. tuberculosis but not in any BCG strain nor in themajority of NTM.
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Comparison between TST and IGRAs
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Collection of blood sample
(3ml) in QFN tubes containing
MTB antigens
T-SPOT.TB QFN-G-IT
1/2
ho
ur
(h)
ha
nd
s-o
n t
ime
fo
r 1
sam
ple
4 h
ha
nd
s-o
n t
ime
fo
r 2
0 s
am
ple
s
No
ha
nd
s-on
time
1 h
ha
nd
s-o
n t
ime
fo
r
1 to
20
sa
mp
les
1 h h
an
ds-o
n tim
e
for 1 to
20
sam
ple
s
Overnight incubation
First day
Second day
ELISPOT
Count spots by naked eyeor using a plate reader
Centrifugation of tubesto harvest the IFN-gamma released
ELISA
Read the concentration of
IFN-gamma by means
of an automated reader
Collection of blood sample (8ml)
and centrifugation
Count PBMCs using a counting chamber
Addition of 250,000 cells per wellwith the MTB specific antigens
Isolation of PBMCs and washing
Overnight incubation
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Higher specificity than TST
in BCG-vaccinated patients
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Association with the degree of
exposure to a patient with active TB
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Association with the degree of
exposure to a patient with active TB
De Souza-Galvao M. 2012.
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Higher number of positive results
in immunosuppressed patients
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IGRAs are less afected
by the immunosuppression than TST…
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Latorre I. ERS. Amsterdam 2011
…although they are also affected
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They followed a cohort of 954 contacts during 4 years. Among the 147 that did not
receive treatment with a positive QFN, 19 (12.9%) developed active TB,
while only 17 out of 551 (3,1%) with a TST>5mm developed active TB.
Positive and negative predictive value
Diel R. AJCCM 2010
Among the 824 contacts that did not receive treatment and with a negative QFN,
none of them progressed to disease, confirming the high NPV of the test.
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Bakir. AIM 2008
908 children from contacts studies were included. During a period of 1.3 years of follow-up,
children with positive T-SPOT.TB had a risk of developing TB between 3 and 4 times higher
than patients with a negative T-SPOT.TB.
However, ratios of progression for T-SPOT-TB and TST were similar (3.86 vs 3.28).
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Positive and negative predictive value
The PPV using commercial IGRAs was 2.7%,
compared with 1.5% for the TST (P<0.0001)
The PPV increased to 6.8% and 2.4%
for IGRAs and TST, respectively,
when only high-risk groups were considered
(P=0.0001)
The NPV for progression
for IGRAs was 99,7%,
and of 99.4% for the TST
(P=0.01)
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668 Contacts
Follow-up during
30 months
284LTBI
TST positive and/orQFN positiveProphylaxis
98QFN & TST negativesPrimary prophylaxis
(in all cases a negative resultwas obtained two moths later)
286No LTBI
TST & QFN negatives,or positives but no
candidates x prophylaxis
8 active TB (All have
QFN i TST positive)
QFN-G-IT
• VPP=15%
• VPN=100%
PT
• VPP = 3%
• VPN = 99%
Positive and negative predictive value
Altet N. Submited 2012.
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Remote infection?
147 HCWs
95 with
previous positive TST
T-SPOT.TB
(%)
POS45
(47.4)
NEG49
(51.6)
IND1
(1.1)
QFN-G-IT
(%)
POS34
(35.8)
NEG59
(62.1)
IND2
(2.1)
In 24 HCWs with both
IFN-gamma tests
negatives and non BCG
vaccinated PST was
performed (%)POS
2(20)
Test invalid in
14 cases
NEG8
(80)
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IGRAs are not useful for diagnosing active TB
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Diagnosis of active TB
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Monitorization of the treatment
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0 6 12 18 24 300
500
1000
1500
2000
Follow up, months
ES
AT
-6-s
pe
cif
ic I
FN
-g
SF
C /
10
6 P
BM
C
0 6 12 18 24 300
500
1000
1500
2000
Follow up, months
CF
P-1
0-s
pe
cif
ic I
FN
-g
SF
C /
10
6 P
BM
C
ESAT-6 CFP-10
There is a high inter-individual variability in the
celular response and in the amount of IFN-γ
released, during the treatment, and in addition, in a
substancial proportion of patients the results of the
IGRA remain positive althouhg they have finished
the treatmentMillington. J.Immunol 2007
Monitorization of the treatment
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Conclusions
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• Exposure and risk factor
association
• Higher specificity (no affected by BCG). Reduce unnecessary
prophylaxis.
• PPV higher/similar than TST and very good NPV
• Less afected by
immunosuppressor
treatments
IGRAs
• Improve positive predictive
value: differentiate between
those persons who will
develop TB and those who will not.
• Remote vs. recent infection
• Infection vs. active TB
• Monitoring of the treatment
• Severe immunosuppression
Waiting for the future…
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The next generation of IGRAs
I have
a dream !
IGRAS
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POSITIVE CONTROL
NEGATIVE CONTROL
SPECIFIC REMOTE
INFECTION ANTIGENS
SPECIFIC RECENT
INFECTION ANTIGENS
SPECIFIC ACTIVE TB ANTIGENS
PACIENT REMOTELY INFECTED
PACIENT RECENTLY INFECTED
PACIENT WITH ACTIVE
TB