Latent tuberculosis infection
Identifying LTBI among possible contacts
Isoniazid prophylactic therapy
Iveta Ozere
State Center of TB and Lung Diseases of
Riga Eastern Clinical University Hospital
Riga Stradins University, Department of Infectology
September 27, 2012
1
The pathway of M.tuberculosis infection
The pathway from M.tuberculosis exposure to
disease is a multistep process that partly
depends on the body’s own immune defences
 Tubercle bacilli may cause disease immediately after
becoming infected or lay persistant for long periods
 Only 5-10% of infected adult people with normal
immune system go on to develop active disease during
their life time
2
The biological nature of persistent M.tuberculosis
infection (1)
The biological nature of a persistent infection with
M.tuberculosis that may or may not cause TB disease is
discussed controversially, but still not clearly understood
 In persons with intact cell-mediated immunity collection of activated T
cells and macrophages form granulomas that limit multiplication and
spread of the organism
 For the majority of individuals with
normal immune function, proliferation
of M. tuberculosis is arrested once
cell-mediated immunity develops,
even though small numbers
of viable bacilli may remain
within the granuloma
3
The biological nature of persistent
M.tuberculosis infection (2)
Granulomas are dynamic lesions with cells
continuously dying, debris being removed, and new
cells entering
When cells are prevented from entering, the
granulomatous structure disintegrates leading to
the dissemination of its content
4
Interaction between M.tuberculosis and
HIV infection
The best-known factor driving progression of latent
infection with M.tuberculosis towards active TB disease
is human immunodeficiency virus (HIV) co-infection
 HIV-infected persons, especially those with low CD4 counts,
develop tuberculosis disease rapidly after becoming infected
with M. tuberculosis; up to 50% of such persons may do so in
the first 2 years after infection with M. tuberculosis
 Conversely an individual who has a prior latent infection with
M.tuberculosis (not treated) and then acquires HIV infection
will develop tuberculosis disease at an approximate rate of 5–
10% per year
5
Exposure, latent TB infection with
M.tuberculosis and active TB disease
Active TB disease
Clinically and radiologically
manifest disease
Latent infection with M.tuberculosis
Person have a positive reaction to the TST
and/or IGRAs test, negative bacteriologic
studies, and no clinical, bacteriological and
radiological evidence of active TB disease
Exposure
Person do have a history of exposure, but
have a negative reaction to the tuberculin
skin test and/or IGRAs
6
Active TB
disease
Exposure
and
latent
tuberculosis
infection
(Ilustrētā zinātne,2006)
7
Detection of latent infection with
M.tuberculosis (LTBI)
It is not currently possible to directly identify
tubercle bacilli from persons latently infected with
M.tuberculosis who do not have active TB disease
However, M.tuberculosis infection induces a strong
cellular immune response dominated by T-helper
cell type 1 CD4 cells, which secrete Interferon y
(IFN-y); the measurement of cellular immune
response can serve as a sensitive marker for the
presence of small numbers of dormant bacilli
8
Immunological diagnosis of
latent TB infection
Currently, two immune-based test principles
for the diagnosis of infection with
M.tuberculosis exist:
 «in vivo» tuberculin skin test
 «in vitro» Interferon-y release assays (IGRAs)
9
Tuberculin skin test
Tuberculin skin test measures cell-mediated
immunity in the form of a DTH response to
purified protein derivative (PPD) of tuberculin
 Tuberculin is a purified protein derivative (PPD)
prepared from a culture filtrate of tuberculosis bacilli by
precipitation
 Tuberculin is a crude mixture of antigens, many of
which are shared by M.tuberculosis , M.bovis, M.bovis
BCG and several species of environmental mycobacteria
10
Immunologic basis for the tuberculin
reaction
 T cells sensitised by prior infection are
recruited to the skin site and release
lymphokines
 Lymphokines induce induration through
local vasodilatation, oedema, fibrin
deposition and recruitment of other
inflammation cells to the area
 Typically the reaction to tuberculin begins
5 to 6 hours after injection, causes maximal
induration at 48 to 72 hours, and subsides
over a period of days
11
Tuberculin skin test by Mantoux method
 Basis of reading is the presence or
absence of induration, which may be
determined either by palpation alone
or palpation and the ball-point
method
 The diameter of induration should be
measured transversely to the long
axis of the forearm and recorded in
mm
12
Drawbacks of TST
Low specificity in Bacille Calmette-Guerin (BCG)
vaccinated individuals due to cross-reactivity of PPD
antigens between BCG and M.tuberculosis
Poor sensitivity in patients with suppressed or
immature cellular immunity (HIV infection,
iatrogenic immunosuppression, or young children)
Two visits required
13
Interferon-y release assays (IGRAs) (1)
Background information on IGRAs
 The cytokine interferon-y (IFN-y) is produced by different cells of
the immune system: CD4 T-cells, CD8 T-cells and Natural Killer
cells
 IFN-y is considered to play an important role in the elimination of
M.tuberculosis by activating the production of reactive oxygen
and nitrogen intermediates in macrophages, which in turn are
involved in the destruction of bacterial pathogens
 T-cells specifically recognizing M.tuberculosis antigens ,
particularly CD4 cells, produce IFN-y essential for the activation of
M.tuberculosis infected macrophages, which upon activation, can
target M.tuberculosis bacilli and control their growth
14
Interferon-y release assay (IGRAs) (2)
Background information on IGRAs
 Genes encoding the production of ESAT-6 and CFP-10 are
deleted from BCG region 1(RD1), and are not present in most
non-tuberculosis mycobacteria (exceptions are M.kansasii,
M.szulgai, M.flavescens, and M.marinum). These antigens
are highly specific indicators of M.tuberculosis infection
 IGRAs are blood-based tests assessing the presence of
effector and memory immune response directed against the
M.tuberculosis specific antigens
 In persons with M.tuberculosis infection, effector/memory T
cells (particularly CD4) produce interferon–γ (IFN- γ) in
response to M.tuberculosis specific antigens ESAT-6, CFP 10,
and in one of the available tests, the TB7.7 antigen
15
Commercially available IGRAs
 QuantiFERON-TB Gold In-Tube assay (QFT-GIT)
 detects the level of IFN-y produced in response to the
M.tuberculosis specific antigens ESAT-6, CFP-10, and
TB7.7, and uses the enzyme-linked immunosorbent assay
(ELISA) detection method
 T-SPOT.TB assay
 measures the number of IFN-y producing T-cells in
response to M.tuberculosis antigens ESAT-6 and
CFP-10, and is based on the enzyme-linked
immunosorbent spot (ELISPOT) assay
16
T-SPOT.TB test
Negative control
Positive control with FHA
Antigen CFP-10
Antigen ESAT-6
17
Immune response of the infected
macrophage
Infected
macrophage
IL-12
Tly
IFN-γ
Activation of
macrophages
18
Advantages and disadvantages of IGRAs
 IGRAs detect the presence of persistent cellular immune
response towards the M.tuberculosis-specific antigens ESAT6, CFP-10 and TB7.7, which are known to be absent in most
of the non-tuberculosis mycobacteria (except M.flavescens,
M.marinum, M.kansasii and M.szulgai) as well as in BCG
strains
 IGRAs are not confounded by previous BCG vaccination and
will be less likely to be confounded by an individuals
previous exposure to non-tuberculosis mycobacteria
 IGRAs cannot distinquish between active TB and LTBI
19
Comparison of performance of Mantoux test and IGRAs
A.Lalvani, M.Thillai. Diagnosis of tuberculosis: principles and practise of using interferon-y release assays (IGRAs).
Breathe, 2009, 5 (4): 303-309.
20
Summary sensitivity of IGRAs and the tuberculin skin test
Diagnostics
Subiect
Summary
sensitivity (95% CI)
Sensitivity range
QFT-G
TB patients, adult
0,80 (0,78-0,82)
0,62-0,95
QFT-G-IT
TB patients, adult
0,74 (0,69-0,78)
0,64-0,93
QFT-G/G-IT
TB patients, child
0,82 (0,75-0,87)
0,53-1,00
T.SPOT
TB patients
0,90 (0,86-0,93)
0,83-1,00
QFT-G/G-IT, T-SPOT
HIV-infected
patients
0,70 (0,60-0,79
0,63-0,85
TST
Healthy subiects
0,77 (0,71-0,82)
0,57-1,00
C.G.Erkens, M.Kamphorst, I.Abubakar et al. Tuberculosis contact investigation in
low prevalence countriwes: a European concensus. Eur Respir J, 2010; 36: 925-949
21
Latent infection with M.tuberculosis (LTBI)
 Whether LTBI depends on the presence of living
mycobacteria is presently unclear
 From the operational point of view, latent
infection with M.tuberculosis may best be
defined as a state of persistent immune
response to prior acquired M.tuberculosis
antigens without evidence of clinically manifest
tuberculosis
U.Mack, G.B.Migiori, M. Sester et al. LTBI: latent tuberculosis infection or lasting immune
responses to M.tuberculosis? A TBNET consensus statement. Eur Respir J, 2009;33:956973
22
Identifying LTBI in people living with HIV having possible
contact with TB (1)
Tuberculin skin test
 TST relies on a competent immune response to identify people with latent
M.tuberculosis infection
 Reaction to a tuberculin skin test and the presence of a granulomatous
reaction in tissues requires a functional Th1 cytokine response
 In HIV-infected persons the sensitivity of the TST is markedly diminished
especially as the CD4 count declines
 During active TB, the tuberculin skin test is positive (> 5 mm diameter in
the absence of previous BCG vaccination and > 10 mm diameter in those
who have been vaccinated with BCG) in 30% of HIV-infected patients with
a CD4 cell count < 200/mm3, and in 50% of those who present with
> 200/mm3
L. Aaron, D. Saadoun, I. Calatroni et al. Tuberculosis in HIV-infected patients: a
comprehensive review. Clinical Microbiology and Infection, 2004; 10 (5): 388-398.
23
Identifying LTBI in people living with HIV having
possible contact with TB (2)
WHO. Guidelines for intensified tuberculosis case-finding and
isoniazid preventive therapy for people living with HIV in resourceconstrained settings. 2010.
Key recommendations
TST is not a requirement for initiating
Isoniazid preventive therapy (IPT) in
people living with HIV in resource
constrained settings
Strong recommendation, moderate quality
of evidence
24
Identifying LTBI in people living with HIV having
possible contact with TB (3)
 Multiple studies in people living with HIV demonstrate that
IPT is more effective in people with a positive TST than in
those with a negative test
 The use of TST could reduce the number of patients
receiving IPT and the numbers needed to treat to prevent
one case of active TB
 Given that TST-positive patients benefit more from IPT than
those who are TST negative, the TST test can be used when
feasible
 People living with HIV who are TST negative should be assessed on
case-by-case basis for their individual risk of TB exposure and the
added advantage of the provision of IPT
WHO. Guidelines for intensified tuberculosis case-finding and isoniazid preventive therapy
for people living with HIV in resource-constrained settings. 2010.
25
Identifying LTBI in people living with HIV having
possible contact with TB (4)
WHO. Guidelines for intensified tuberculosis case-finding and isoniazid
preventive therapy for people living with HIV in resource-constrained
settings. 2010.
Key recommendations
People living with HIV who have a positive TST
benefit more from IPT; TST can be used where
feasible to identify such individuals
Strong recommendation, high quality of evidence
26
Identifying LTBI in people living with HIV having
possible contact with TB (5)
Interferon-gamma release assays (IGRAs)
 The performance of IGRAs is compromised among
people living with HIV compared to those without HIV
 Significantly higher rates of indeterminate test results
are found with QFT-G-IT test in persons with HIV
compared to persons without HIV, and in persons with
low CD4 cell counts compared to persons with higher
CD4 cell counts
 Sensitivity of IGRAs are markedly reduced among
patients with low CD4 counts
WHO. Guidelines for intensified tuberculosis case-finding and isoniazid preventive
therapy for people living with HIV in resource-constrained settings. 2010.
27
Identifying LTBI in people living with HIV
having possible contact with TB (6)
WHO. Guidelines for intensified tuberculosis case-finding and
isoniazid preventive therapy for people living with HIV in resourceconstrained settings. 2010.
Key recommendations
Based on the available evidence, the Guidelines
Group concluded, that IGRA are not
recommended to screen people living with HIV
for eligibility to receive IPT
28
Isoniazid preventive therapy for
people living with HIV (1)
There are two important strategies for
preventing active TB disease in people living
with HIV:
early initiation of ART and
Isoniazid preventive therapy
29
Isoniazid preventive therapy for people living
with HIV (2)
Rationale of IPT of LTBI
 Of the currently available antituberculosis drugs, Isoniazid has the
highest early bactericidal activity against rapidly growing tubercle bacilli
 Mutants resistant to antituberculosis drugs are known to emerge
spontaneously through alterations of chromosomal genes. For Isoniazid,
such mutants are sought to arise in one in 107 to 109 cell divisions,
resulting in one effectively resistant M.tuberculosis bacillus in 106 of the
bacillary population
 The propensity for emergence of resistance might be less with the much
lower bacillary load as is the case with latent infection with
M.tuberculosis
30
Isoniazid preventive therapy for people living
with HIV (3)
WHO. Guidelines for intensified tuberculosis case-finding and isoniazid
preventive therapy for people living with HIV in resource-constrained
settings. 2010.
Key recommendations
Providing IPT to people living with HIV does not
increase the risk of developing Isoniazid
resistant TB
Strong recommendation, moderate quality of
evidence
31
Isoniazid preventive therapy for people living
with HIV (4)
Active TB disease
Clinically and radiologically
manifest disease
Latent infection with M.tuberculosis
Preventive treatment
LTBI
Person have a positive reaction to the TST
and/or IGRAs test, negative bacteriologic
studies, and no clinical, bacteriological and
radiological evidence of active TB disease
Exposure
Post-exposure treatment
of presumed infection
Person do have a history of exposure, but
have a negative reaction to the tuberculin
skin test and/or IGRAs
32
Isoniazid preventive therapy for people living
with HIV (5)
 Treatment with Isoniazid for 6-12 months reduced the risk of
tuberculosis by 60% over two years or longer in HIV noninfected patients
(Smieja M, Marchetti C, Cook D et al. Isoniazid fro preventing tuberculosis in non-HIV
infected person. Cochrane Database Syst rev 2010; 1:CD000171)
 A 12 months course of Isoniazid reduced the incidence rate
of TB from 7,5 to 2,2 per 100 person-years among HIVinfected subjects. In subgroup analysis, there was significant
reduction among TST-positive subjects, but not among TSTnegative subjects
(Whalen CC, Johnson Jl, Okwera A et al. A trial of three regimens to prevent tuberculosis
in Ugandan adults infected with the human immunodeficiency virus infection who are at
high risk for tuberculosis. N Engl J Med 1997; 337:315-320)
33
Isoniazid preventive therapy for people living
with HIV (6)
 A completed course of IPT in PLHs with a positive TST
prevents up to 60-70% of active TB disease cases for a period
that ranges from 6 to 18 months
Quigley MA, Mwinga A, Hosp M, et al. Long term effect of preventive therapy for
tuberculosis in a cohort of HIV-infected Zambian adults. AIDS 2001: 15:215-222.
 ART and IPT, when used together, may have an additive
effect and decrease TB incidence by 50-80%
Golub JE, Saraceni V, Cavalcante SC, et al. The impact of antiretroviral therapy and isoniazid
preventive therapy on tuberculosis incidence in HIV-infected patients in Rio de Janeiro, Brazil.
AIDS 2007;21:1441-1448.
34
Isoniazid preventive therapy for people living
with HIV (7)
 The optimal duration of Isoniazid for the prevention of
tuberculosis in HIV-seropositive individuals is unclear.
Both a 6-months regimen and a 12-months regimen are
effective , but none of the trials directly compared
isoniazid regimens of different durations
(C.C. Leung, H.L. Rieder, C. Lange and W.W. Yew. Treatment of latent infection with
Mycobacterium tuberculosis: update 2010. Eur Respir J, 2011;37: 690-711)
 The protection of Isoniazid treatment in HIV-infected
persons appears to be short lasting (1-2,5 years)
(C.C. Leung, H.L. Rieder, C. Lange and W.W. Yew. Treatment of latent infection with
Mycobacterium tuberculosis: update 2010. Eur Respir J, 2011;37: 690-711)
35
Isoniazid preventive therapy for people living
with HIV (8)
Isoniazid prophylaxis was safe but ineffective as
preexposure prophylaxis against TB in HIV-infected
and HIV-uninfected children
Shabir A. Madhi, Sharon Nachman, Avy Violari, Soyeon Kim, Mark F.Cotton, Raziya
Bobat, Patrick Jean-Philippe, George McSherry, Charles Mitchell. Primary Isoniazid
pprophylaxis against Tuberculosis in HIV-Exposed Children. N Engl J Med 2011;
365:21-31.
36
Isoniazid preventive therapy for people living with HIV (9)
WHO. Guidelines for intensified tuberculosis case-finding and isoniazid
preventive therapy for people living with HIV in resource-constrained settings.
2010.
Key recommendations
Adults and adolescents living with HIV who have an unknown or
positive TST status and are unlikely to have active TB should receive
at least six months of IPT as part of a comprehensive package of HIV
care. IPT should be given to such individuals irrespective of the
degree of immunosuppression, and also to those on ART, those who
have previously been treated for TB and pregnant women.
Strong recommendation, high quality of evidence
Isoniazid at 300 mg/day remains the drug of choice for
chemotherapy to prevent TB in adults living with HIV.
37
Isoniazid preventive therapy for people living with HIV (10)
WHO. Guidelines for intensified tuberculosis case-finding and
isoniazid preventive therapy for people living with HIV in resourceconstrained settings. 2010
Key recommendations
 Adults and adolescents living with HIV who have an unknown or
positive TST status and are unlikely to have active TB should
receive at least 36 months of IPT.* IPT should be given to such
individuals irrespective of the degree of immunosuppression, and
also to those on ART, those who have previously been treated for
TB and pregnant women
Conditional recommendation, moderate quality of evidence
* The consideration for implementation should include the local context
such as the epidemiology of TB and HIV, and setting with the highest rates
of prevalence and transmission of TB among people living with HIV
38
Isoniazid preventive therapy for people living with HIV (11)
WHO. Guidelines for intensified tuberculosis case-finding and isoniazid preventive
therapy for people living with HIV in resource-constrained settings. 2010
Key recommendations
 All children living with HIV who are more than 12 months of age and who are
unlikely to have active TB on symptom-based screening, and have no contact
with TB case should receive 6 months isoniazid preventive therapy
(10 mg/kg/day) as part of a comprehensive package of HIV prevention and care
services
Strong recommendation, moderate quality of evidence
 Children living with HIV who are less than 12 months of age, only those children
who have contact with TB case should receive 6 months of Isoniazid preventive
therapy, if the evaluation shows no TB disease
Strong recommendation, low quality of evidence
 All children living with HIV who have successfully completed treatment for TB
diseases should receive Isoniazid for an additional six months
Conditional recommendation, low quality of evidence
39
3.4.5. What must be
considered when deciding
to initiate an isoniazid
preventive therapy
programme in a country?
40
3.4.5. What must be considered when deciding to initiate an
isoniazid preventive therapy programme in a country? (1)
Ministries of health and national AIDS and TB control
programmes should consider both technical and programmatic
issues when assessing their readiness to implement and
monitor an IPT programme in a country. These points include:
 How well does the proposed clinical, symptom-based algorithm in the
country predict TB disease? Is it possible that persons with active TB disease
are missed, and if so, how many are there? What is the role of chest
radiography in finding persons with active TB disease who would have
otherwise been missed. The answers to these questions are essential in
order to minimise the number of persons with active TB disease in whom
isoniazid monotherapy may lead to the development of isoniazid resistance
 Even in high TB burden settings, not everyone has latent TB infection. In this
country, is it appropriate to start IPT (in all age groups) without a TST?
41
3.4.5. What must be considered when deciding to initiate an
isoniazid preventive therapy programme in a country? (2)
 A positive TST indicates infection with M.tuberculosis but does no
differentiate between infection and active disease. A false-positive TST
could result from previous BCG vaccination or exposure to
environmental mycobacteria. A negative TST result does not exclude TB
disease. Persons with severe immune suppression from HIV may not
react to a TST even if they do have TB. Interferon-gamma release assays
(IGRAs) cannot differentiate between TB disease and latent infection
either and are not recommended due to lack of data
 In deciding the optimal duration of IPT, there should be a grasp of the
relative importance of re-infection versus re-activation among TB cases.
If the former is responsible for the majority of cases, lifelong IPT may
becoma a consideration. On the other hand, lifelong and even shorter
IPT courses pose several challenges regarding treatment adherence
among PLHs who are well and have no symptoms of TB disease.
42
3.4.5. What must be considered when deciding to initiate an
isoniazid preventive therapy programme in a country? (3)
 Does the TB or HIV programme take responsibility for IPT implementation?
The current WHO recommendation is that national AIDS control
programmes (NAPs) manage IPT as one aspect of the HIV care package that
is provided in HIV care sites. However, NAPs should coordinate closely with
the national TB control programmes (NTPs) for the procurement of isoniazid,
because of its use for preventing TB in close contacts of persons with TB,
especially children under the age of fives years (an activity that is NTPs
responsibility)
 Does the country have the human and logistical resources to embark on
developing and scaling up an IPT programme, especially if the current cure
rate for TB cases has not yet reached international targets and/or if ART
coverage is not yet universal?
 Is there a budget for isoniazid? Who will order it and ensure that adequate
stocks of single-dose isoniazid are available? In addition, pyridoxine should
also be stocked for persons taking IPT
 Does the country have a recording and reporting system for an IPT
programme?
43
Thank You for attention
Questions?
44
References
1.
C.G. Erkens, M. Kamphorst, I. Abubakar, G.H. Bothamley, D. Chemtob, W. Haas, G.B. Migiliori, H.
Rieder, J.P. Zellweger and C. Lange. Tuberculosis contact investigation in low prevalence countries:
a European concensus. Eur Respir J, 2010; 36: 925-949
2. A.Lalvani, M.Thillai. Diagnosis of tuberculosis: principles and practise of using interferon-y release
assays (IGRAs). Breathe, 2009; 5 (4): 303-309.
3. Europea Centre for Disease Prevention an s Control. Use of interferon-gamma release assays in
support od TB diagnosis. Stockholm: ECDC; 2011.
4. L.Aaron, D. Saadoun, I.Calatroni, O.Launay, N.Memain, V.Vincent, G.Marchal, B.Dupont,
O.Bouchaud, D.Valeyre, O.Lortholary. Tuberculosis in HIV-infected patients: a comprehensive
review. Clinical Microbiology and Infection, 2004; 10 (5): 388-398.
5. WHO. Guidelines for intensified tuberculosis case-finding and isoniazid preventive therapy for
people living with HIV in resource-constrained settings. 2010.
6. Selwyn PA, Hartel D, Lewis VA, et al. A prospective study of the risk of tuberculosis among
intravenous drug users with human immunodeficiency virus infection. N Engl J Med 1989; 320:
545-550.
7. C.C. Leung, H.L. Rieder, C. Lange and W.W. Yew. Treatment of latent infection with Mycobacterium
tuberculosis: update 2010. Eur Respir J, 2011;37: 690-711.
8. Golub JE, Saraceni V, Cavalcante SC, et al. The impact of antiretroviral therapy and isoniazid
preventive therapy on tuberculosis incidence in HIV-infected patients in Rio de Janeiro, Brazil.
AIDS 2007;21:1441-1448
9. Quigley MA, Mwinga A, Hosp M, et al. Long term effect of preventive therapy for tuberculosis in a
cohort of HIV-infected Zambian adults. AIDS 2001: 15:215-222.
10. Shabir A. Madhi, Sharon Nachman, Avy Violari, Soyeon Kim, Mark F.Cotton, Raziya Bobat, Patrick
Jean-Philippe, George McSherry, Charles Mitchell. Primary Isoniazid prophylaxis against
Tuberculosis in HIV-Exposed Children. N Engl J Med 2011; 365:21-31.
11. U.Mack, G.B.Migiori, M. Sester et al. LTBI: latent tuberculosis infection or lasting immune
responses to M.tuberculosis? A TBNET consensus statement. Eur Respir J, 2009;33:956-973
45