Mady Slater, M.D. Stanford University Medical Center Division of Infectious Diseases 04/23/14 WOEMA webinar Conflict of Interest Disclosures: I have no financial relationships with commercial entities producing, marketing, reselling, or distributing health care goods or services consumed by, or used on, patients relevant to the content I am planning, developing, presenting, or evaluating.
Content Attestation I, Madeline L. Slater, hereby declare that the content for this activity, including any presentation of therapeutic options, is well balanced, unbiased, and to the extent possible, evidence-based. Objectives To distinguish active TB from latent TB infection (LTBI) To describe and compare approved diagnostic tests for LTBI To review guidelines on the usage of IGRAs and discuss clinical scenarios To describe the observed variability in serial testing; to list potential sources of variability; to describe quality assurance measures to minimize variability To outline areas of clinical uncertainty
Tuberculosis epidemiology Over 2 billion individuals are thought to be latently infected with M. tuberculosis (WHO, 2009). Lifetime risk of development of active disease from latent TB infection (LTBI) 5-10% Globally, 9 million people develop active TB annually 2 million people die annually from TB WHO 2009 Pathogenesis of Tuberculosis http://pathport.vbi.vt.edu/pathinfo/pathogens/tuberculosis_2.html
TB Pathogenesis- 3 outcomes: #1: Immune clearance #2: Latent TB Infection (LTBI) Within 2 to 8 weeks macrophages surround the pathogen and form a granuloma These cells form a barrier that keeps the bacilli contained and under control (LTBI) Not infectious Adapted from CDC TB teaching slides: Module 1 Transmission and Pathogenesis of Tuberculosis 7 TB Pathogenesis- 3 outcomes: #3: TB Disease If the immune system CANNOT keep tubercle bacilli under control, bacilli multiply and cause disease Can occur at any time, with LTBI 5-10% lifetime risk Infectious Adapted from CDC TB teaching slides: Module 1 Transmission and Pathogenesis of Tuberculosis 8
LTBI vs. TB Disease Latent TB Infection (LTBI) Inactive, contained tubercle bacilli in the body TB Disease (in the lungs) Active, multiplying tubercle bacilli in the body Chest x-ray usually normal Sputum smears and cultures negative No symptoms Not infectious Not a case of TB Chest x-ray usually abnormal Sputum smears and cultures may be positive Symptoms such as cough, fever, weight loss Often infectious before treatment A case of TB Module 1 Transmission and Pathogenesis of Tuberculosis 9 Targeted TB testing Screening should be targeted to those at higher risk of TB, NOT the general population Target populations with: Increased rates of recent TB infection Increased risk of progression to active TB Goals: Identify active TB cases Identify LTBI that would benefit from rx Surveillance
Risk of TB Infection Contacts/converters Recent immigrants Targeted TB Testing **If no risk, don t order the test- increased risk of false positives.** Residents/employees of high-risk congregate settings (corrections, nursing home, dialysis unit) Risk of TB Progression HIV Abnl CXR suggestive of prior TB < 5 years of age Foreign-born from high risk Diabetes countries (High urden countries: http://www. stoptb.org/countries/tbdata.asp) Health care workers (HCWs) Immunosuppression (prednisone, chemo, TNF lpha inhibitor) Medically underserved (homeless or marginally housed, migrant workers, street drug users, children with pare nts Other medical: silicosis, gastrectomy, low body weight/malnutrition, malabsorption, head/neck cancer, organ transplant, jejunoilieal bypass Smoking, IVDU, alcoholism TB testing in HCWs Goal: to identify and treat those truly infected to prevent progression to active TB while to avoid inappropriate treatment for LTBI with associated hepatotoxicities
HCW TB screen components Baseline testing upon hire: ymptom screening and review of risks wo step TB skin test (TST) or single Interferon Gamma Release Assay (IGRA). If new positive: CXR f previously positive, in general need documented TST or IGRA result ; Need for CXR based on local regulations. Annual testing: - Determine need based upon annual risk assessment OR local regulation TB risk screen includes: Prior TB infection/disease, treatment Prior TB testing TB symptom review Medical conditions / risk factors Sociodemographic factors HIV status
LTBI Testing -No gold standard since there is no way to microbiologically diagnose LTBI -Must use proxy of the host immunologic response to TB antigens to infer the diagnosis Diagnosis of LTBI from 1908 to Dec 2006 - TST Disadvantages - Subjective - In vivo - Adverse effects - Boosting - Affected by BCG vaccination and non-tuberculous mycobacteria - Requires two visits
IGRAs entered the scene in 2006-2007 with a lot of promise. A 21st Century Solution for Latent TB Detection Many medical centers have switched to IGRAs for LTBI screening QFT-GIT Advantages -1 step testing -Automated -Improved specificity in BCG vaccinated and individuals with nontuberculous mycobacterial infection -Likely more cost-effective -No boosting QFT-GIT Disadvantages -Blood draw -Performance data in long term studies lacking -Caution in young children, immunocompromised/hiv -Serial testing showing high variability
IGRA Interpretation Memory T cell CD 4 IFN-γ + Antigen presenting cell APC QFT-ELISA quantifies IFNgamma T-SPOT- Elispot detects activated memory T cells ESAT6 CFP-10 TB7.7 Test Positive Negative Grey zone Ind. QFT 0.35 IU/ml* <0.35 IU/ml* None Controls fail: -High nil -Low mitogen T-spot TB 8 spots* < 8 spots* 5 spots* Same * (TB Ag - Nil) and assumes appropriate control responses
What is the QFT assay? The QFT assay is comprised of 3 tubes: -Antigen: inside of tube is coated with TB-specific antigens -Nil: contains heparin and serves as a negative control. -Mitogen: contains phytohaeamagluttinin (PHA) and serves as positive control providing information about correct blood sample handling and the immune status of pt ELISA is performed in all 3 tubes to measure the Interferon-gamma level (IU/ml) ***QFT result (IU/ml)= Antigen-Nil*** How do IGRAs perform? Key performance characteristics of any diagnostic: -Sensitivity (true positive proportion identified) -Specificity (true negative proportion identified) HOWEVER, ability to assess performance limited by lack of gold standard for LTBI diagnosis -Most accepted method is testing populations with known characteristics (ie active TB patients for sensitivity estimates and low risk individuals for specificity estimates)
Accuracy of the current LTBI diagnostics Sensitivity (%) Specificity (%) TST 89 85 T.SPOT.T 90 88 B QFT 81 99 Mazurek MMWR 2010. CDC 2010 MMWR IGRA Recommendations IGRA preferred Persons with likely poor return rate for TST reading Persons who have received BCG vaccine
CDC 2010 MMWR IGRA Recommendations IGRA or TST recommended (without preference) Recent contacts to person infected with TB Periodic screening of HCWs While routine testing with both TST and IGRA is not recommended, consider both if If the initial test is negative AND There is high risk of infection, progression, or poor outcomes (HIV positive, < 5 years of age, immunocompromised) There is high clinical suspicion of active TB If the initial test is positive AND There is need for additional evidence to encourage compliance It is a healthy person with low risk of both infection and progression
TST vs. IGRA: What to do with discordant results Avoid using two tests for TB screening TST(+) / IGRA( Foreign born with BCG and no severe immunocompro mising condition attribute to BCG - Caveat: abnormal CXR consistent with old TB + risk factor for progression to disease, consider treatment U.S. born with no risk factors for exposure or risk factors for progression may be NTM colonization TST vs. IGRA: What to do with discordant results TST( / IGRA(+) Foreign born with BCG and no severe immunocompro mising condition consider repeat IGRA if near cutoff point, e.g. TB Ag i l < 0.7 U.S. born with no risk factors for exposure or progressi on epeat IGRA If discordant TST/ IGRA and severe immunocompromising condition, offer LTBI treatment If severe immunocompromising condition and if TST I GRA and
What about indeterminates? The 2 main causes of indeterminate results are: Lack of incubating the samples properly (such as not incubating the sample at all or over incubating) Insufficient mixing of blood collection tubes Other less common causes are outlined below: Recent patient illness Recent vaccinations Lymphocytes responding indiscriminately (recent patient bouts with poison ivy, rheumatoid arthritis, etc.) Lack of response to phytohaemagglutinin (occurs in less than 1 in 1,000 patients) Storage of filled blood collection tubes outside the recommended temperature range (22 C ± 5 C) prior to 37 C ± 1 C incubation Insufficient lymphocytes Inability of the patient s lymphocytes to generate IFN-γ Quantiferon Package Insert If the QFT result is indeterminate Repeat the test If the repeat is indeterminate, then IGRA can t be used for clinical decision making, except to assume that the patient is probably anergic. Other tests (ie TST), clinical information, TB risk factors and risk of progression must be used instead.
Additional clinical IGRA pearls IGRAs should not be used to monitor response to TB therapy; studies in this area are inconsistent. The CDC and WHO advises against the use of both IGRAs and TST for diagnosis of active TB. IGRAs cannot accurately predict the risk of infected individuals developing active TB disease There is limited evidence on timing of IGRA conversions. Most evidence show IGRA conversions occur within four to eight weeks after exposure but conversion after three months has been reported QFT Reproducibility Serial testing is the largest market for the QFT. -Annual HCW screening -Some contact investigations -TB vaccine trials FDA approval for serial testing based on running samples from 8 individuals 3 times
QFT Conversions In serial testing, conversions are defined as negative positive at a threshold of 0.35 IU/mL (no consideration of magnitude of change) Reversions are positivenegative Van Zyl-Smit et al, 2009 CDC guidelines in 2005 recommended use of IGRAs for HCW screening with: no published data on serial testing no independent, peer-reviewed literature on IGRA reproducibility
Since 2006, >50 studies have assessed IGRAs in HCWs Thorax 2012 Early adopters of IGRAs for HCW screening in the US are reporting interesting challenges (and some hospitals are coming up with their own interpretational criteria and cut-offs!)
Reproducibility of QFT-IT in HCW Prospective study of >2000 HCWs (CDC Task Order 18 study): TST = 0.9 % QFT = 6.1% T-SPOT = 8.3% conversion rate Largest study of 9155 HCWs (Slater et al, AJRCCM 2013): TST = 0.4% Historical rate QFT = 4.3% conversion rate Coversions 2% to 15% Reversions 20% to 80% Canadian study in HCWs (Zwerling et al. PLoS ONE 2013): TST = 0% QFT = 5.3% Pai conversion and Elwood Can raterespir J. 2012 Dorman et al. AJRCCM 2014 Slater et al. AJRCCM 2013 Updated CDC Recommendations 2005 CDC recommendations: An IGRA or a TST may be used without preference for periodic screening of persons who might have occupational exposure to M. tuberculosis (e.g., surveillance programs for health-care workers). 2010 updated recommendations: Reiterates the above but cautions the disadvantages include a greater risk of test conversion due to false-positive IGRA results with follow-up testing of low-risk health-care workers who have tested negative at prior screening.
QFT serial test results for all Stanford HCWs during the study period. Slater et al, AJRCCM 201 QFT serial test results for HCWs with conversion on annual testing and subsequent short-term QFT repeat testing (within 60 days)
New Cut-off? 1.0 If cut-off is raised to 1IU/ml, short-term reproducibility is improved from 55% to 78% BUT 51% of persistent positives are missed (assumption: persistent positive individuals truly have LTBI) Within-subject QFT variability studies are emerging (independent of manufacturers)
Identified sources of IGRA Variability - Pre-analytical - Analytical - Manufacturing - Immunological Image from Banaei, Clinical Microbiology Reviews Cover Image, in press QFT identified sources of variability - Pre-analytical - Skin disinfection - Blood volume - Shaking of tubes - Incubation delay - Incubation temp - Incubation duration - Plasma storage - Analytical - ELISA - Immunologic - Infection - Antibiotics - Diet - TST boosting - Time of blood draw - Manufacturing - Endotoxin contamination
Manufacturing defects: The QFT-GIT Surveillance Graph Showing Daily Positive Rate at Stanford Elevated rate noted TBAg lot discontinued Within-subject Comparison of QFT Results 31% vs 5% n=463 Slater et al JCM 2012
FDA informed via CDC. Investigation Outcomes Cellestis conducted an internal investigation and could not reproduce our findings. We could not culture viable organisms. Highlighted the importance of surveillance of positive rates Cellestis improved their quality control program resulting in the recall of endotoxin contaminated tubes An additional episode occurred July-October 2013 Slater et al, JCM 2012 Slater et al, CID 2014 Known significant source of variability: Incubation delay TB Response Following Immediate and Delayed Incubation Per protocol, incubation delay 0-16 hour range n=128 Doberne et al JCM 2011
Analytical Sources of variability Refer to fluctuations in measurements due to random errors caused during the ELISA- no way to minimize these with technique. Most ELISA-based diagnostics account for the variability with an indeterminate zone when interpreting results Surprising that QFT has dichotomous cutoff Multiple studies have shown considerable withinrun, between-run, and between-laboratory variability in results, producing discordant results when QFT value is near the cut-off Metcalfe et al AJRCCM 201 QFT research-next steps With individual sources of variability identified, the composite effect on QFT results should be identified Currently testing an optimized protocol -Improve reproducibility -Quantify the within subject variability to guide QFT interpretation
Conclusions If IGRAs are being used for HCW screening, re-evaluate TB risk factors and risk of progression in new conversions. If low risk, retest. Be aware of concern of missing true LTBI if an increased cutoff is used. If large scale QFT testing is being done, consider implementing a surveillance of rates of positive and indeterminate results. Incubate QFT specimens as soon as possible after draw Await more data to guide improved interpretation criteria for QFT Acknowledgements Stanford University Niaz Banaei, MD Upi Singh, MD Julie Parsonnet, MD Occupational health clinic staff Financial Support Stanford SPARK/ Global Health McGill Madhukar Pai, MD, PhD
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