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The TB Risk Assessment

The TB Risk Assessment . VDH TB Control and Prevention Program 2011. Why do a TB risk assessment?. Identify those in need of further testing for TB disease Meet job or program requirements Identify those who would benefit from treatment for latent TB infection, thus preventing TB disease.

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The TB Risk Assessment

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  1. The TB Risk Assessment VDH TB Control and Prevention Program 2011

  2. Why do a TB risk assessment? • Identify those in need of further testing for TB disease • Meet job or program requirements • Identify those who would benefit from treatment for latent TB infection, thus preventing TB disease

  3. Persons at Risk for Developing TB Disease • Those who have been recently infected • Those with clinical conditions that increase their risk of progressing from LTBI to TB disease Persons at high risk for developing TB disease fall into 2 categories:

  4. Recent Infection as a Risk Factor • Close contacts to person with infectious TB • Skin test or IGRA converters (within past 2 years) • Recent immigrants from TB-endemic regions of the world (within 5 years of arrival to the U.S.) • Children ≤ 5 years with a positive TST • Residents and employees of high-risk congregate settings (e.g., correctional facilities, homeless shelters, health care facilities)

  5. Increased Risk for Progression to TB Disease • A history of prior, untreated TB or fibrotic lesions on chest radiograph suggestive of past TB • Underweight or malnourished persons • Injection drug users • Those receiving TNF-α antagonists for treatment of rheumatoid arthritis or Crohn’s disease • Persons with certain medical conditions such as HIV, DM, CRF/dialysis, silicosis, organ transplant, CA of head/neck, gastrectomy or jejunoilial bypass

  6. TB Screening or TB Testing • For more than a decade it has been recognized that the TST is less sensitive in low risk populations • TB Screening, where a patient is asked a variety of questions by a health care provider, is a more sensitive way to identify who needs further testing. Ask about: • Symptoms • Risk for acquiring TB infection • Risk for progressing to TB disease if infected

  7. Occupations Where TB Screening is Acceptable • Assisted living employees • Foster care parents • Day care employees • School employees • Residential school attendees *TST or IGRA is indicated if there is a risk factor on the risk screen A chest x-ray is indicated for positive TST or IGRA A full diagnostic work-up is needed if symptoms consistent with TB

  8. Who can sign the “free from TB” statement? • Physician • Public Health Nurse or Clinician • Physician’s Assistant or Nurse Practitioner if for Adult Day Care

  9. Who needs the TST or IGRA? (regardless of risk screening) • Health care workers • Students preparing for health care careers • Adult day care participants • Anyone who will be serially tested with TST or IGRA • All persons before taking any TNFα antagonist drugs (Remicade, Humira, Enbrel, Kineret, Rituxan, etc.)

  10. Diagnosis of TB Infection:Mantoux TB Skin Test (TST) • One way to evaluate for TB infection • Is the preferred type of skin test (vs. tine or multi-puncture tests) • Is useful in: • Screening people for TB infection (contacts and targeted testing) • Examining those with symptoms of TB disease

  11. The Tuberculin Skin Test or TST

  12. The tuberculin skin testing (TST) • In use for more than 100 years (1890) • 0.1 ml of 5 tuberculin units of purified protein derivative (PPD) administered intradermally • Evaluated (read) 48 to 72 hours after administration • Cross reacts with other mycobacteria, including BCG vaccine • A history of BCG vaccine is not a contraindication

  13. TST Result: False Positive • Possible causes • Non-tuberculousmycobacteria • BCG vaccination • Routinely administered to children in countries where TB is prevalent • Not a contraindication for the administration of the TB skin test • Wanes over time ; if TST is + likely due to TB infection if risk factors present

  14. TST Result: False-Negative • Causes include • Anergy / immune suppression • Recent TB infection (within past 10 weeks) • Very young age (younger than 6 months old) • Incorrect administration and storage of test solution • Live-virus vaccination within 4-6 weeks • Overwhelming TB Disease • Poor TST administration technique

  15. Administering Mantoux TST • Ask about any history of previous positive TST • Inject 0.1 ml of 5 tuberculin units of liquid tuberculin, intradermally, using a 27 gauge needle with bevel up • Use the volar surface of forearm when possible • May use the scapular area if forearm • Produce a wheal 6 to 10 mm in diameter • Advise no creams, band-aids, scratching • May shower or swim • Record the site, lot number, date and time of administration, and person giving the test

  16. Reading the Mantoux TST • Examine the patient’s arm 48-72 hours after the tuberculin is injected • Assess the injection site for erythema (redness) and induration (swelling that can be felt) by lightly palpating the area • Measure the diameter the indurated (raised area only, across the forearm, recording in millimeters (do not measure the erythema) • Record the date, time, size of induration in millimeters, interpretation (positive or negative), and follow-up recommended

  17. Interpreting the TST Results • Interpretation takes into account the patient’s individual risk factors for TB infection and progression to disease • Cut points for positivity are at 5, 10, and 15 mm • It is necessary to know the patient’s history (TB risk assessment) to determine an individual patient’s TST interpretation

  18. Interpretation of the TST:Persons Positive at > 5 mm • People with HIV infection • Close contacts of people with infectious TB • Persons with fibrotic chest x-ray findings suggestive of prior TB disease • Patients with organ transplants • Persons immunosuppressed for other reasons (on TNF-a drugs, or the equivalent of >15 mg/day of prednisone for 1 mo. or longer)

  19. Interpretation of the TST: Persons Positive at > 10 mm • Recent immigrants (< 5 years) • Injection drug users • Residents and employees of high-risk congregate settings • Mycobacteriology laboratory personnel • People with clinical conditions that place them at high risk (those listed on risk screen) • Children < 4 years old • Infants, children and adolescents exposed to adults in high-risk groups

  20. Interpretation of the TST: Persons Positive at > 15 mm • An induration of 15 or more millimeters is considered positive in any person, including persons with no known risk factors for TB. • Targeted skin testing programs should only be conducted among high-risk groups.

  21. Reading the TST • Educate patient and family regarding significance of a positive TST result • Positive TST reactions can be measured up to 7 days after administration • Negative reactions must be read between 48-72 hours after administration

  22. Other Issues in Skin Testing • Booster Phenomena • ability to react to tuberculin may wane with time • a TST may prompt new antibody production • a second TST detects this “boosted,” increased response • Two-step testing – two TSTs, 1 to 3 weeks apart • Use with groups who will have repeated TSTs as part of infection control programs • Avoids a “boosted” test classified as new positive, which could reflect undetected transmission

  23. Interferon Gamma Release Assay – the TB blood test or IGRA

  24. Basic Principles of IGRA testing • Peripheral blood lymphocytes from a person suspected of having tuberculosis infection are exposed to antigens (different from those in PPD/more specific) from Mycobacterium tuberculosis • If person has been infected with M. tuberculosis, lymphocytes will respond by producing IFN-γ • The tests measure the total IFN-γ produced (QFT-GIT) or number of cells that produce IFN-γ (T.Spot TB)

  25. Interferon Gamma Release Assays – The TB blood tests • An equally acceptable choice for TB infection testing • Preferred for those with Hx of BCG vaccination – no cross reactivity with BCG vaccine • Do cross react with a few NTMs • May be preferred for those who are not likely to return for TST reading (SA, homeless, etc.) • Two types of tests approved by the FDA • QuantiFERON TB Gold-in-Tube or QFT-GIT • T-Spot TB • Results are both quantitative and qualitative

  26. QuantiFERON TB Gold-in-Tube Sample Results

  27. T Spot Sample Result

  28. Comparison of IGRA vs. TST IGRA TST Two visits (4 for two-step test) Cross reacts with BCG with potential for false positives Time frame constraint for reading Less expensive than IGRA More subjective determination of results Unreliable results for children under age 6 months • One visit • No cross reaction with BCG • Limited time frame from draw to incubation in lab • More expensive than TST • Less subjective determination of results • Not approved for children under age 5 years

  29. Commonalities between TST and IGRA • BOTH dependent on a functioning immune system • If negative, neither rule out TB disease • Generally, not recommended to be used sequentially, i.e. one to confirm the other

  30. ?? Questions ??

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