Diagnosis of Tuberculosis Diagnosis of Tuberculosis 2010 2010 New Tools, Tricks, Thinking? New Tools, Tricks, Thinking? John Bernardo, M.D. John Bernardo, M.D. Pulmonary Section, Pulmonary Section, Boston University School of Medicine Boston University School of Medicine Massachusetts Department of Public Health Massachusetts Department of Public Health Objectives Objectives • Primary Priority: Diagnosis of Tuberculosis, 2010 • Target the Reservoir: Identify Latent TB Infection History History • 26 y/o F physician from S. Asia – Pos TST (22mm) on pre-employment evaluation – Exam and CXR: neg – Offered treatment for LTBI, but declined • “It’s my BCG – in my country everyone has a positive test” • 8 months later presents with fatigue/malaise, cough x 4+ wk, fever – MD prescribed antibiotic (Levaquin ® ) • Symptoms improved – did not clear -- then returned • 2 MD visits later (and 2 more courses abx later): Saskatchewan Lung Association
15
Embed
Diagnosis of Tuberculosis 2010 Objectives New Tools ...globaltb.njms.rutgers.edu/downloads/courses/Section 4a - Dx of TB.pdf · in Context • Older gentleman from homeless shelter
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Diagnosis of Tuberculosis Diagnosis of Tuberculosis 20102010
New Tools, Tricks, Thinking?New Tools, Tricks, Thinking?
John Bernardo, M.D.John Bernardo, M.D.Pulmonary Section, Pulmonary Section,
Boston University School of MedicineBoston University School of MedicineMassachusetts Department of Public HealthMassachusetts Department of Public Health
ObjectivesObjectives
• Primary Priority: Diagnosis of Tuberculosis, 2010
• Target the Reservoir: Identify Latent TB Infection
HistoryHistory
• 26 y/o F physician from S. Asia– Pos TST (22mm) on pre-employment evaluation– Exam and CXR: neg– Offered treatment for LTBI, but declined
• “It’s my BCG – in my country everyone has a positive test”
• 8 months later presents with fatigue/malaise, cough x 4+ wk, fever– MD prescribed antibiotic (Levaquin®)
• Symptoms improved – did not clear -- then returned
• 2 MD visits later (and 2 more courses abx later):
Saskatchewan Lung Association
OOPSOOPS
Sputum 4+ smear positive
MTD+: MTb Complex
Diagnosis of TB, 2010Diagnosis of TB, 2010Some things change; Some donSome things change; Some don’’tt
• Diagnosis follows “Suspicion”• When should we “Think TB”?
– Who is at risk for TB?– Is TB presenting differently than in the past?– How do we make the diagnosis? – And … are there new ways to improve
diagnostic capacity?
Diagnosis: Define Groups atDiagnosis: Define Groups at--RiskRiskEpidemiology of recent cases
• In US– Majority of cases is non-US born; from high prevalence countries– Community-specific (e.g., homeless, substance abusers, Haitians, …)– Children from high-prevalence groups
• Medical risk factors (if infected)– HIV 7-10%/yr– Diabetes ? 4%/yr – ESRD 10-20%/yr– Immunosuppressive therapies – including Organ transplant recipients,
anti-TNF-α agents, chronic steroids– Age
• Recent transmission versus reactivation
Elderly US-born still appear (born when TB still widely endemic) Still a problem; usually represent reactivation disease
Diagnosis of TBDiagnosis of TB
• History (personal)• Symptoms
– Specific to system involved• e.g., cough (pulmonary), chest pain (pericardial), …
–– 3030--90% for sputum90% for sputum–– Least sensitive detection method: detects 10Least sensitive detection method: detects 1044
AFB/ml (improved w fluorescent stain to 10AFB/ml (improved w fluorescent stain to 1033/ml)/ml)•• Specificity: poorSpecificity: poor•• Advantages: Advantages:
–– Detection of potentially Detection of potentially infectiousinfectiouscasescases
–– May be used to monitor treatmentMay be used to monitor treatment
–– Better than smear: 10 Better than smear: 10 –– 100 AFB/ml can be detected100 AFB/ml can be detected–– 80 80 –– 90% of US cases are culture positive90% of US cases are culture positive
•• Specificity: excellent Specificity: excellent (the Gold Standard)(the Gold Standard)
•• Advantage:Advantage:–– Rapid identification Rapid identification once growing once growing (gene probes) (gene probes) –– Confirms diagnosis (if positive)Confirms diagnosis (if positive)–– Can use for drug susceptibilities (adds weeks)Can use for drug susceptibilities (adds weeks)–– Can use to monitor treatmentCan use to monitor treatment
•• Time: 7Time: 7--21 days21 days•• Sensitivity: variesSensitivity: varies•• Specificity: very good to excellentSpecificity: very good to excellent•• Advantage:Advantage:
–– More rapid identification of organism (gene probes)More rapid identification of organism (gene probes)–– Confirms diagnosis (if positive)Confirms diagnosis (if positive)–– Can use for rapid drug susceptibilities (simultaneous)Can use for rapid drug susceptibilities (simultaneous)
•• Two tests approved by FDA: MTD and Two tests approved by FDA: MTD and AmplicorAmplicor–– MTDMTD approved for smearapproved for smear--pos or pos or negneg sputum/respiratory secretionssputum/respiratory secretions
•• False positive: contaminants; patient on treatmentFalse positive: contaminants; patient on treatment•• False negative: inhibitors of the reaction; low volumeFalse negative: inhibitors of the reaction; low volume
•• Predictive value is influenced by MD index of suspicion and Predictive value is influenced by MD index of suspicion and population testedpopulation tested
•• Still need cultureStill need culture–– Identification & drug susceptibility testing (DST)Identification & drug susceptibility testing (DST)
•• Recommended for initial sputum in new, Recommended for initial sputum in new, realreal suspectssuspects–– Should become Standard of CareShould become Standard of Care
Unlikely that M.tbwill be grown from sample (if controlled for inhibitor)
CDC: MMWR, 1/16/09
Rapid Molecular Detection of Drug ResistanceMolecular Beacon (rt-PCR-based) Assays*
Rapid Molecular Detection of Drug ResistanceRapid Molecular Detection of Drug ResistanceMolecular Beacon (Molecular Beacon (rtrt--PCRPCR--based) Assays*based) Assays*
if no mutation is detected in target region →fluorescence
if target contains mutation, beacon will not anneal → no fluorescenceE. Desmond,
CA State Laboratory
* not FDA-approved
Genes Associated with INH and RMP Resistance
• Rif resistance– rpoB core region (>95%)
• INH resistance– katG, inhA, ahpC, ndh (~85%)
E. Desmond, CA State Laboratory
Rapid Molecular Testing for Rifis available from CDC-TB Lab
Identification of Identification of M.tbM.tb by Differential DNA Fluorescence Stainingby Differential DNA Fluorescence StainingUsing Flow CytometryUsing Flow Cytometry
Courtesy: N. Pearlmutter, H. Shapiro
Courtesy: N. Pearlmutter, H. Shapiro
A Minimalist Imaging CytometerA Minimalist Imaging Cytometer
Latent TB Infection
Primary TB in a Child
- Delayed-type Hypersensitivity develops 8-10wk post-infection: TST or IGRA-positive
Latency of M. tuberculosis
• Environment of granuloma favors altered metabolism:• Low pO2• Reduced CHO• High Fat
• Replication time >>> 20hr.• Loss of acid fast staining properties• Mechanism(s) unknown
• Genetic switch?
• Lifetime risk of Reactivation
- Tubercle bacilli - “dormant”- Usually positive TST/IGRA- No symptoms- Normal Examination- Normal chest radiograph- NOT infectious- Sputum smears and cultures are negative
- Not a “case” of TB
Latent TB InfectionATS/CDC LTBI Recommendations:*
Diagnostic Testing and Treatment
Target testing to TB high risk- Contacts, medical conditions, homeless, prisoners- Recent immigrants, TST-neg w recent travel, underserved
Do NOT test- Low-risk persons- Known TST-pos- Recent (6wk) live virus vaccination (TST)
Populations for LTBI therapy- High TB-risk (including over 35), including recent immigrants- High TB-risk pregnant women
TST+ (IGRA+) and risk stratification ≡ “infected”Process:
- Hx, PE, and CXR for infected individuals- If NO evidence of disease: LTBI
** AJRCCM, April, 2000AJRCCM, April, 2000
Frequency of Screening
Whom should be retested, and how often?– Depends on ongoing risk of TB exposure
– Re-test your patients who have extended travel to high risk areas or other possible exposures (e.g., healthcare workers with potential TB exposure)
The New Immigration Process A Giant Step
• IMMIGRANTS, REFUGEES, and TBScreened in country of origin: – Evaluated for active TBactive TB
•• CXR, sputum smear/cultureCXR, sputum smear/culture•• Complete treatment prior to leavingComplete treatment prior to leaving
– Children (<15 y/o) undergo skin testing • In the US
– Those applying for an adjustment of status are evaluated for LTBI but treatment is not mandatedtreatment is not mandated
• Not evaluated:– Visitors, students, temporary workers, undocumented
CDC
Administering the TST
Create wheal6-10mm diam.
Reading the Skin TestReading the Skin Test
• Read @ 48-72 hours• Must be measured by
a professional TRAINEDTRAINED to read TB Skin Tests
• Size of the “bump” is measured, recorded in mm
10mm10mm
5mm5mm
15mm15mm
Interpretation of TSTDepends on patient risk
Size of TST
Who should be considered positive?
> 5 mm 1. Immunosuppressed person, especially HIV+2. Close contact of infectious TB case 3. Lesion on CXR consistent with old TB
> 10 mm 1. From a high incidence group (e.g., from area where TB is endemic such as certain countries, prisons, nursing homes, homeless shelters; intravenous drug users; medical risks)
2. Recent TST converter (defined: 2 yr; >10mm increase)> 15 mm 1. No known risk factors for TB
BCG - Bacille Calmette Guerin
• Derived from a strain of M. bovis• Not accepted/recognized in U.S. as
protection against TB• Not standardized vaccine• Efficacy studies range from 0-80% • Can confound tuberculin skin test
– But consider patient to be TB infected if TST positive
• In vitro assays for cell-mediated immunity to M. tuberculosisantigens– Utilize whole blood– Measure release of IFN-γ by circulating T lymphocytes following
stimulation with TB antigens (specific)• QuantiFERON®-TB approved by FDA in 2001 as “… an aid to
the diagnosis of TB infection.”• QFT-Gold test US FDA approved in 2005• QFT-Gold in-Tube test approved 2007• T Spot®-TB test approved 2008• Revised Guidelines, June, 2010
Interpreting IGRA ResultsInterpreting IGRA Results
• Negative: Same interpretation as negative TST• Positive: Same interpretation as positive TST
– Medical evaluation and chest x-ray are still needed to exclude TB disease and confirm LTBI
• Indeterminate: Test failure– Repeat test
• Borderline: (T-Spot® only) – Repeat test
CDC: MMWR, 6/25/10
Advantages of IGRAs
• Single patient visit• IGRA draw does not “boost” subsequent IGRA tests
– But TST may boost subsequent IGRA
• Less likely positive in BCG-vaccinated: Specificity• “Objective” read-out• Results available in 1-2days• Cost benefits (??)• Culture- and ethnic-naïve
Limitations of IGRAs• Limited data in many groups, such as those with
impaired immune function and children (<5 y/o)• High indeterminate results, poor reproducibility
shown in some studies• No good definition of conversion
– Currently: negative → positive ≡ conversion
• The ability of IGRAs to predict risk of progression to TB disease has not been determined – May be different than in those with a positive TST
• As with TST, IGRAs may be useful as a diagnostic aid within certain clinical contexts – Use judgment when interpreting these tests