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Slide Set — Self Study Modules

Module 3: Targeted Testing and the Diagnosis of Latent TB Infection and TB Disease

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Slide 1 (Title Slide):  Self-Study Modules on Tuberculosis: Targeted Testing and the Diagnosis of Latent Tuberculosis Infection and Tuberculosis Disease

Slide 2: Module 3: Objectives
At completion of this module, learners will be able to:

  1. Identify high-risk groups for targeted testing
  2. Describe how to give and interpret a Mantoux tuberculin skin test (TST) and an interferon-gamma release assay (IGRA)
  3. Discuss considerations for using either the TST or IGRA for diagnosing infection with M. tuberculosis
  4. Describe the components of a medical evaluation for diagnosing TB disease

Slide 3: Module 3: Overview

  • Targeted Testing
  • Diagnosis of latent tuberculosis infection (LTBI)
    • TST
    • IGRAs
    • TB Testing Programs, the Booster Phenomenon, and Two-Step Testing
  • Diagnosis of TB Disease
  • Reporting  of TB Cases
  • Case Studies

Slide 4: (Title Slide) Targeted Testing

Slide 5: Targeted Testing (1)

  • Targeted testing is a TB control strategy used to identify and treat persons:
    • At high risk for infection with M. tuberculosis
    • At high risk for developing TB disease once infected with M. tuberculosis

Slide 6: Targeted Testing (2)

  • Identifying persons with LTBI is an important goal of TB elimination because LTBI treatment can:
    • Prevent the development of TB disease
    • Stop the spread of TB

Slide 7: Targeted Testing (3): A Decision to Test is a Decision to Treat

  • TB testing activities should be done only when there is a plan for follow-up care
  • Health care workers (HCWs) should identify and test persons who are at high risk
    • People who are not at high risk generally should not be tested

Slide 8: Targeted Testing (4): High-Risk Groups

  • High-risk groups can be divided into two categories:
    • People who are at high risk for becoming infected with M. tuberculosis
    • People who are at high risk for developing TB disease once infected with M. tuberculosis

Slide 9: Targeted Testing (5): High-Risk Groups for TB Infection

  • Close contacts of people known or suspected to have TB
  • People who have come to U.S. within 5 years from areas where TB is common
  • Low-income groups
  • People who inject drugs

Slide 10: Targeted Testing (6): High-Risk Groups for TB Infection

  • People who live or work in high-risk settings
  • HCWs who serve high-risk clients
  • Racial or ethnic minority populations
  • Infants, children, and adolescents exposed to adults in high-risk groups

Slide 11: Targeted Testing (7): High-Risk Groups for TB Disease

  • People living with HIV
  • People recently infected with M. tuberculosis (within past 2 years)
  • People with certain medical conditions known to increase risk for TB
  • People who inject drugs
  • Infants and children younger than 4 years old

Slide 12: (Title Slide) Diagnosis of Latent TB Infection (LTBI)

Slide 13: Diagnosis of LTBI

  • Available testing methods for M. tuberculosis infection:
    • Mantoux tuberculin skin test (TST)
    • Blood tests known as interferon-gamma release assays (IGRAs):
      • QuantiFERON®-TB Gold test (QFT-G)
      • QuantiFERON®-TB Gold In-Tube (QFT-GIT)
      • T-SPOT

Slide 14: (Title Slide) Diagnosis of Latent TB Infection (LTBI): Mantoux Tuberculin Skin Test: Administering the Test.

Slide 15: Mantoux Tuberculin Skin Test (1)

  • TST is administered by injection
  • Tuberculin is made from proteins derived from inactive tubercle bacilli
  • Most people who have TB infection will have a reaction at injection site

[IMAGE: Syringe being filled with 0.1 ml of liquid tuberculin]

Slide 16: Mantoux Tuberculin Skin Test (2)

  • 0.1 ml of 5 tuberculin units of liquid tuberculin are injected between the layers of skin on forearm

[IMAGE: Health care worker administering Mantoux TST on patient’s forearm]

Slide 17: Mantoux Tuberculin Skin Test (3)

  • Forearm should be examined within 48 - 72 hours by HCW
  • Reaction is an area of induration (swelling) around injection site
    • Induration is measured in millimeters
    • Erythema (redness) is not measured

[IMAGE: Health care worker measuring the area of induration on patient’s forearm with a TB skin test ruler]

Slide 18: Multiple-Puncture Test

  • In the past, multiple-puncture tests (tine tests) were a popular skin testing method for TB
  • No longer recommended
    • Amount of tuberculin that enters skin cannot be measured
  • Mantoux TST is preferred TB skin test method because amount of tuberculin can always be measured

Slide 19: Mantoux Tuberculin Skin Test Study Question 3.1

  • What is the TST used for? (pg. 11)
    • The TST is used to determine whether a person has TB infection.

Slide 20: Mantoux Tuberculin Skin Test Study Question 3.2

  • How is the Mantoux TST given? (pg. 11)
    •  The TST is given by a needle and syringe to inject 0.1 ml of 5 tuberculin units of liquid tuberculin between the layers of the skin, usually on the forearm.

Slide 21: Mantoux Tuberculin Skin Test Study Question 3.3

  • With the TST, when is the patient’s arm examined? (pg. 12)
    • The patient’s arm is examined by a health care worker, 48 – 72 hours after tuberculin is injected.

Slide 22: Mantoux Tuberculin Skin Test Study Question 3.4

  • How is the induration measured? (pg. 12)
    • The diameter of indurated area is measured across the forearm; erythema (redness) around the indurated area is not measured.

Slide 23: Mantoux Tuberculin Skin Test Study Question 3.5

  • Why is the Mantoux TST preferable to multiple puncture tests? (pg. 12)
    • Mantoux TST is preferable because it is more accurate and the amount of tuberculin can always be measured.

Slide 24: (Title Slide) Diagnosis of Latent TB Infection: Mantoux Tuberculin Skin Test: Interpreting the Reaction

Slide 25: Mantoux Tuberculin Skin Test (4): Interpreting the Reaction

  • Interpretation of TST reaction depends on size of induration and person’s risk factors for TB

[IMAGE: Health care worker measuring the area of induration on patient’s forearm with a TB skin test ruler]

Slide 26:  Mantoux Tuberculin Skin Test (5): Interpreting the Reaction

  • Induration of > 5 mm is considered positive for:
    • People living with HIV
    • Recent close contacts of people with infectious TB
    • People with chest x-ray findings suggestive of previous TB disease
    • People with organ transplants
    • Other immunosuppressed patients

Slide 27: Mantoux Tuberculin Skin Test (6): Interpreting the Reaction

  • Induration of > 10 mm is considered a positive reaction for:
    • People who have recently come to U.S. from areas where TB is common
    • People who inject drugs
    • People who live or work in high-risk congregate settings
    • Mycobacteriology laboratory workers

Slide 28: Mantoux Tuberculin Skin Test (7): Interpreting the Reaction

  • Induration of > 10 mm is considered a positive reaction for:
    • People with certain medical conditions that increase risk for TB
    • Children younger than 4 years old
    • Infants, children, or adolescents exposed to adults in high-risk categories

Slide 29:  Mantoux Tuberculin Skin Test (8): Interpreting the Reaction

  • Induration of > 15 mm is considered a positive reaction for people who have no known risk factors for TB

Slide 30:  Mantoux Tuberculin Skin Test Study Question 3.6

  • What 2 factors determine the interpretation of a skin test reaction as positive or negative? What additional factor is considered for people who may be exposed to TB on the job? (pg. 16)
    • Size of induration and risk factors for TB
    • An additional factor is the risk of exposure to TB in the person’s job

Slide 31: Mantoux Tuberculin Skin Test Study Question 3.7

  • For which groups of people is > 5 mm of induration considered a positive reaction? Name 4. (pg. 16)
    • People living with HIV
    • Recent contacts of people with infectious TB
    • People who have had TB disease before
    • Patients with organ transplants and other immunosuppressed individuals

Slide 32: Mantoux Tuberculin Skin Test Study Question 3.8

  • For which groups of people is > 10 mm of induration considered a positive reaction? (pg. 17)
    • Recent arrivals to the U.S. from areas where TB is common
    • People who inject drugs
    • Mycobacteriology lab workers
    • People who live or work in high-risk congregate settings
    • People with certain medical conditions
    • Children younger than 4 years old
    • Infants, children, and adolescents exposed to adults in high-risk categories

Slide 33: Mantoux Tuberculin Skin Test Study Question 3.9

  • For which group of people is > 15 mm of induration considered a positive reaction? (pg. 17)
    • People with no risk factors for TB.

Slide 34: (Title Slide) Diagnosis of Latent TB Infection (LTBI): Mantoux Tuberculin Skin Test: Factors that Affect the Reaction

Slide 35: Mantoux Tuberculin Skin Test (9): False-Positive Reaction

  • Factors that can cause people to have a positive reaction even if they do not have TB infection:
    • Infection with nontuberculous mycobacteria
    • BCG vaccination
    • Administration of incorrect antigen
    • Incorrect measuring or interpretation of TST reaction

Slide 36: Mantoux Tuberculin Skin Test (10): BCG Vaccine

  • People who have been vaccinated with BCG may have a false-positive TST reaction
    • However, there is no reliable way to distinguish between reaction caused by TB infection or by BCG vaccine
  • Individuals should always be further evaluated if they have a positive TST reaction

Slide 37:  Mantoux Tuberculin Skin Test (11): False-Negative Reaction

  • Factors that can cause false-negative reactions:
    • Anergy
    • Recent TB infection (within past 8 – 10 weeks)
      • It can take 2 – 8 weeks after TB infection for body’s immune system to react to tuberculin
    • Younger than 6 months of age
    • Recent live-virus (e.g., measles or smallpox) vaccination
    • Incorrect method of giving the TST
    • Incorrect measuring or interpretation of TST reaction

Slide 38:  Mantoux Tuberculin Skin Test (12)

  • Any patient with symptoms of TB disease should be evaluated for TB disease, regardless of his or her skin test reaction.

[IMAGE: Doctor examining a patient.]

Slide 39:  Mantoux Tuberculin Skin Test (13): Anergy

  • Inability to react to skin tests due to weakened immune system
  • Anergy testing is no longer routinely recommended

Slide 40:  Mantoux Tuberculin Skin Test Study Question 3.10

  • Name 4 factors that can cause false-positive reactions to the TST. (pg. 19)
    • Infection with nontuberculous mycobacteria (NTM)
    • BCG vaccination
    • Administration of incorrect antigen
    • Incorrect measuring or interpretation of TST reaction

Slide 41:  Mantoux Tuberculin Skin Test Study Question 3.11

  • Is there a reliable way to distinguish a positive TST reaction caused by vaccination with BCG from a reaction caused by true TB infection? (pg. 19)
    • No. Individuals who have had BCG vaccine should be further evaluated for LTBI or TB disease the same way as if they were not vaccinated with BCG.

Slide 42: Mantoux Tuberculin Skin Test Study Question 3.12

  • Name 6 factors that can cause false-negative reactions to the TST. (pg. 24)
    • Anergy
    • Recent TB infection (within past 8-10 weeks)
    • Very young age
    • Recent live-virus (e.g., measles or smallpox) vaccination
    • Incorrect method of giving the TST
    • Incorrect measuring or interpretation of TST reaction

Slide 43:  Mantoux Tuberculin Skin Test Study Question 3.13

  • What is anergy? (pg. 24)
    • The inability to react to skin tests because of a weakened immune system.

Slide 44: Mantoux Tuberculin Skin Test Study Question 3.14

  • After TB has been transmitted to someone, how long does it take before TB infection can be detected by the TST? (pg. 24)
    • 2 - 8 weeks

Slide 45:  Mantoux Tuberculin Skin Test Study Question 3.15

  • What should be done if a patient has a negative TST result, but has symptoms of TB disease? (pg. 25)
    • Any patient with symptoms of TB disease should be evaluated for TB disease, regardless of his or her skin test reaction.

Slide 46: (Title Slide) Diagnosis of Latent TB Infection (LTBI): Interferon-Gamma Release Assays (IGRAs)

Slide 47:  Types of IGRAs

  • QuantiFERON®-TB Gold (QFT-G)
    • CDC guidelines published in 2005
  • QuantiFERON®-TB Gold In-Tube (QFT-GIT)
    • Approved 10/2007
  • T-Spot®.TB test (T-SPOT)
    • Type of ELISpot assay
    • Approved 7/2008
  • CDC guidelines for IGRAs are under development

 [IMAGE: T-SPOT TB Testing Materials.  Image credit:  U.S. Food and Drug Administration, 2009.]

Slide 48:  QFT-G and QFT-GIT (1)

  • Measures person’s immune reactivity to M. tuberculosis
  • Used to help diagnose M. tuberculosis infection in persons suspected of having either LTBI or TB disease

Slide 49:  QFT-G and QFT-GIT (2): Conducting the Test

  • Follow manufacturer’s instructions
    • Confirm arrangements for delivery and testing of blood within 12 hours of collection
    • Draw sample of blood into tube with heparin
    • Schedule appointment for patient to receive test results
      • If needed, medical evaluation and treatment for LTBI or TB disease

Slide 50: QFT-G and QFT-GIT (3): How it Works

  • Blood samples are mixed with antigens and incubated for 16 - 24 hours
  • If infected with M. tuberculosis, blood cells will recognize antigens and release interferon gamma (IFN-γ) in response
  • Results are based on the amount of IFN-γ released in response to antigens and control substances

Slide 51: QFT-G and QFT-GIT (4): Interpreting Results

  • Test results are based on IFN-γ concentrations
  • Laboratories can use software provided by manufacturer to calculate results
  • Results are sent to requesting clinician

[IMAGE: Processing of QFT-G sample.]

Slide 52: QFT-G and QFT-GIT (5): Report of Results

  • If test result is positive, M. tuberculosis infection likely
  • If test result is negative, M. tuberculosis infection unlikely, but cannot be excluded especially if:
    • Patient has TB signs and symptoms
    • Patient has a high risk for developing TB disease once infected with M. tuberculosis
  • If test result is indeterminate, it means that the test did not provide useful information about the likelihood of M. tuberculosis infection.  Options are to repeat test, administer a TST, or do no additional testing.

Slide 53:  T-SPOT

  • Type of ELISpot assay
  • Interferon gamma is presented as spots from T cells sensitized to M. tuberculosis
  • Results are interpreted by subtracting the spot count of the control from the spot count of the sample

Slide 54:  IGRA Advantages

  • Requires single patient visit to conduct test
  • Results can be available in 24 hours
  • Does not cause booster phenomenon
  • Less likely to have incorrect reading of results as compared to TST
  • BCG vaccination does not affect results

Slide 55:  IGRA Disadvantages and Limitations

  • Blood samples must be processed within 12 hours for some IGRAs
  • Errors in running and interpreting test can decrease accuracy
  • Limited data on its use in certain populations
  • Limited data on its use to determine who is at risk for developing TB disease

Slide 56: QFT-G and QFT-GIT Study Question 3.20

  • What are the steps for conducting a QFT-G and QFT-GIT? (pg. 39)           
    • Read manufacturer’s instructions and follow these steps:
      • Confirm arrangements for delivery and testing of blood in qualified laboratory within 12 hours of collection
      • Draw sample of whole blood from patient into tube with heparin
      • Schedule appointment for patient to receive test results and, if then needed, medical evaluation and possible treatment

Slide 57: QFT-G and QFT-GIT Study Question 3.21

  • How are QFT-G and QFT-GIT results interpreted? (pg. 39)
    • Interpretation is based on the IFN-γ concentrations in the test samples
    • Laboratories can use software to calculate results
    • Report of results are submitted to requesting clinician

Slide 58:  QFT-G and QFT-GIT Study Question 3.22

  • How should a negative QFT-G or QFT-GIT result be interpreted? (pg. 39)
    • Patient is unlikely to have M. tuberculosis infection
    • Patient may not require further evaluation unless they have signs and symptoms of TB disease

Slide 59:  IGRAs Study Question 3.23

  • What are 5 advantages for using an IGRA as compared to the TST? (pg. 39)
    • Requires a single patient visit
    • Results can be available in 24 hours
    • Does not cause the booster phenomenon
    • Less likely to have incorrect reading of results
    • BCG vaccine does not affect IGRA results

Slide 60: (Title Slide) Diagnosis of Latent TB Infection (LTBI): TB Testing Programs, the Booster Phenomenon, and Two-Step Testing

Slide 61: TB Testing Programs (1)

  • Many health care facilities have TB testing programs
    • Employees and residents are periodically given TSTs or IGRAs
  • Testing programs:
    • Identify people who have LTBI or TB disease and give them treatment
    • Determine whether TB is being transmitted in facility

Slide 62: TB Testing Programs (2): Baseline Test

  • Employees and/or residents are given TSTs or IGRAs when they first enter facility
    • If person is negative, they may be retested at regular intervals thereafter

Slide 63:  TB Testing Programs (3): Conversion

  • Persons whose TST or IGRA result converts from negative to positive have probably been infected with M. tuberculosis
    • TST or IGRA conversions may indicate that TB is being transmitted in facility

Slide 64: Booster Phenomenon

  • Phenomenon in which people who are skin tested many years after they became infected with TB have:
    • Negative reaction to initial TST
    • Positive reaction to subsequent TST given up to one year later
  • Occurs mainly in older adults
  • May affect accuracy of baseline skin test

Slide 65: Booster Phenomenon

  • A person is infected with M. tuberculosis.  As the years pass, the person’s ability to react to tuberculin lessens. When the person is skin tested many years after they became infected with M. tuberculosis, they may have a negative reaction. However, this skin test “jogs the memory” of the immune system to recognize and react to tuberculin.  The person is then skin tested again.  The person has a positive reaction.  This is a boosted reaction due to TB infection that occurred a long time ago, not during the time between the two skin tests. (For this example, we assume that the person was not exposed to TB during this time.)

[IMAGE: Flowchart describing the booster phenomenon.  A person becomes infected with M. tuberculosis. As the years pass, the person’s ability to react to tuberculin lessens. The person is skin tested. The person has a negative reaction because he or she has a lessened ability to react to tuberculin. However, this skin test “jogs the memory” of the immune system to recognize and react to tuberculin. Up to 1 year later(For this example, we assume that the person was NOT exposed to TB during this time.) The person is skin tested again. The person has a positive reaction. This is a boosted reaction due to TB infection that occurred a long time ago, not during the time between the two skin tests.Please reference Figure 3.4 The Booster Phenomenon, in Module 3, pg. 28 (pdf)]

Slide 66: Two-Step Testing

  • Only conducted when TST is used
  • Distinguishes between boosted reactions and reactions caused by recent infections
  • Should be used for initial skin testing of persons who will be retested periodically
  • If person’s initial skin test is negative, they should be given a second test 1-3 weeks later
    • Second test positive: probably boosted reaction
    • Second test negative: considered uninfected

Slide 67:  Two-Step Testing

  • A person has a baseline skin test.  The reaction is either positive or negative.  If it is positive, the person probably has TB infection.  If it is negative, the person should be retested 1-3 weeks later.  The reaction is either positive or negative.  If it is negative, the person probably does not have TB infection and the skin test should be repeated at regular intervals; a positive reaction will probably be due to recent TB infection.  If the reaction is positive, the reaction is considered a boosted reaction (due to TB infection that occurred a long time ago) and retesting is not necessary.

[IMAGE: Flow chart describing two-step testing. Baseline skin test. If reaction is positive, person probably has TB infection. If reaction is negative, then retest 1-3 weeks later. If the reaction to the restest is positive, the reaction is considered a boosted reaction (due to TB infection that occurred a long time ago). Retesting not necessary. If reaction to the retest is negative, the person probably does NOT have TB infection. Repeat test at regular intervals; a positive reacton will probably be due to a recent TB infection.  Please reference Figure 3.5 Two-Step Testing, in Module 3, pg. 30 (pdf)]

Slide 68: Booster Phenomenon Study Question 3.16

  • What is the booster phenomenon? (pg. 31)
    • Phenomenon in which people who are skin tested many years after becoming infected with M. tuberculosis have a negative reaction to an initial skin test, followed by a positive reaction to a skin test given up to a year later
    • Occurs because the ability to react to tuberculin lessens over time in some people

Slide 69: Two-Step Testing Study Question 3.17

  • What is the purpose of two-step testing?  (pg. 31)
    • To distinguish between boosted reactions and reactions caused by recent infection.

Slide 70: Two-Step Testing Study Question 3.18

  • In what type of situation is two-step testing used? (pg. 31)
    • It is used in many programs for skin   testing employees when they start their job.

Slide 71: Two-Step Testing Study Question 3.19

  • How is two-step testing done? (pg. 31)
    • If a person has a negative reaction to an initial skin test, he or she is given a second test 1-3 weeks later.
      • If reaction to second test is positive, it is considered a boosted reaction
      • If reaction to second test is negative, person is considered to be uninfected

Slide 72: (Title Slide) Diagnosis of TB Disease

Slide 73:  Medical Evaluation

  • Anyone with TB symptoms or positive TST or IGRA result should be medically evaluated for TB disease
  • Components of medical evaluation:
    1. Medical history
    2. Physical examination
    3. Test for TB infection
    4. Chest x-ray
    5. Bacteriological examination

Slide 74: (Title Slide) Diagnosis of TB Disease: Medical Evaluation

  •  Medical History
  • Physical Examination
  • Test for TB Infection

Slide 75: Medical History (1)

  • Clinicians should ask patients if they have:
    • Symptoms of TB disease
    • Been exposed to a person with infectious TB or have risk factors for exposure to TB
    • Any risk factors for developing TB disease
    • Had LTBI or TB disease before

Slide 76: Medical History (2): General Symptoms of TB Disease

  • Fever
  • Chills
  • Night sweats
  • Weight loss
  • Appetite loss
  • Fatigue
  • Malaise

Slide 77: Medical History (3): Symptoms of Pulmonary TB Disease

  • Cough lasting 3 or more weeks
  • Chest pain
  • Coughing up sputum or blood

Slide 78: Medical History (4): Symptoms of Extrapulmonary TB Disease

  • Symptoms of extrapulmonary TB disease depend on part of body that is affected
  • For example:
    • TB disease in spine may cause back pain
    • TB disease in kidneys may cause blood in urine

Slide 79: Physical Examination

  • A physical examination cannot confirm or rule out TB disease, but can provide valuable information

[IMAGE: Doctor examining a patient.]

Slide 80: Test for TB Infection (1)

  • Types of tests available for diagnosing TB infection in U.S.:
    • TST
    • IGRAs
      • QFT-G
      • QFT-GIT
      • T-SPOT

[IMAGE: QFT-G lab kit]

Slide 81: Test for TB Infection (2)

  • Patients with symptoms of TB disease should always be evaluated for TB disease, regardless of their TST or IGRA test result
    • Clinicians should not wait for TST or IGRA results before starting other diagnostic tests
    • TST or IGRA should be given at the same time as other steps in the diagnosis of TB disease

Slide 82: Diagnosis of TB Disease Study Question 3.24

  • What are the 5 components for conducting a medical evaluation for diagnosing TB disease? (pg. 44)
    • Medical history
    • Physical examination
    • Test for TB infection
    • Chest x-ray
    • Bacteriologic examinations

Slide 83: Diagnosis of TB Disease Study Question 3.25

  • What parts of a patient’s medical history should lead a clinician to suspect TB? (pg. 45)
    • Symptoms of TB disease
    • Exposure to a person who has infectious TB or has other risk factors for exposure to TB
    • Risk factors for developing TB disease
    • TB infection or TB disease in the past

Slide 84: Diagnosis of TB Disease Study Question 3.26

  • What are the symptoms of pulmonary TB disease? What are the symptoms of extrapulmonary TB disease? (pg. 45)
    • General symptoms of TB disease: Weight loss, fatigue, malaise, fever, and night sweats.
    • Pulmonary: Coughing, pain in chest, coughing up sputum or blood.
    • Extrapulmonary: Depends on the part of the body that is affected by the disease.  For example, TB of the spine may cause pain in the back; TB of the kidney may cause blood in the urine.

Slide 85: Diagnosis of TB Disease Study Question 3.27

  • For patients with symptoms of TB disease, should clinicians wait for TST or IGRA results before starting other diagnostic tests?  (pg. 45)
    • No, clinicians should not wait for TST or IGRA results before starting other diagnostic tests.

Slide 86: (Title Slide) Diagnosis of TB Disease: Medical Evaluation

  • Chest X-Ray

Slide 87: Chest X-Ray (1)

  • When a person has TB disease in lungs, the chest x-ray usually appears abnormal.  It may show:
    • Infiltrates (collections of fluid and cells in lung tissue)
    • Cavities (hollow spaces within lung)

[IMAGE: Abnormal chest x-ray with cavity.]

Slide 88: Chest X-Ray (2)

  • Chest x-rays can:
    • Help rule out possibility of pulmonary TB disease in persons who have a positive TST or IGRA result
    • Check for lung abnormalities

Slide 89: Chest X-Ray (3)

  • Chest x-rays cannot confirm TB disease
    • Other diseases can cause lung abnormalities
    • Only bacteriologic culture can prove patient has TB disease
    • Chest x-ray may appear unusual or even appear normal for persons living with HIV

Slide 90: Chest X-Ray Study Question 3.28

  • Name 2 purposes of the chest x-ray. (pg. 47)
    • Help rule out possibility of pulmonary TB disease in a person who has positive TST or QFT-G result and no symptoms of TB
    • Check for lung abnormalities in people who have symptoms of TB disease

Slide 91: Chest X-Ray Study Question 3.29

  • Can the results of a chest x-ray confirm that a person has TB disease? Why or why not? (pg. 47)
    • No.  A variety of illnesses may produce abnormalities on chest x-ray.  Only bacteriologic culture can prove whether or not a patient has TB disease.

Slide 92: (Title Slide) Diagnosis of TB Disease: Medical Evaluation

  • Bacteriologic Examination

Slide 93: Bacteriologic Examination (1)

  • TB bacteriologic examination is done in a laboratory that specifically deals with M. tuberculosis and other mycobacteria
    • Clinical specimens (e.g., sputum and urine) are examined and cultured in laboratory

Slide 94: Bacteriologic Examination (2)

  • Bacteriologic examination has 5 parts
    • Specimen collection
    • Examination of acid-fast bacilli (AFB) smears
    • Direct identification of specimen (nucleic acid amplification)
    • Specimen culturing and identification
    • Drug susceptibility testing

Slide 95: Bacteriologic Examination (3): Specimen Collection

  • For pulmonary TB, specimens can be collected by:
    • Sputum sample
    • Induced sputum sample
    • Bronchoscopy
    • Gastric washing

[IMAGE: A TB patient in a special sputum collection booth coughing up sputum into a sterile container. The booth prevents the spread of tubercle bacilli.]

Slide 96: Bacteriologic Examination (4): Specimen Collection

  • Easiest and least expensive method is to have patient cough into sterile container
  • HCWs should coach and instruct patient
  • Should have at least 3 sputum specimens examined
    • Collected in 8-24 hour intervals
    • At least one early morning specimen

Slide 97: Bacteriologic Examination (5): Induced Sputum Collection

  • Induced sputum collection should be used if patient cannot cough up sputum on their own
  • Patient inhales saline mist, causing deep coughing
  • Specimen often clear and watery, should be labeled “induced specimen”

Slide 98: Bacteriologic Examination (6): Bronchoscopy

  • Bronchoscopy may be used:
    • If patient cannot cough up enough sputum
    • If an induced sputum cannot be obtained
  • Procedure:  instrument is passed through nose or  mouth into lung to obtain pulmonary secretions or lung tissue

[IMAGE: A doctor and a nurse performing a bronchoscopy on a patient.]

Slide 99: Bacteriologic Examination (7): Gastric Washing

  • Usually only used if sample cannot be obtained from other procedures
  • Often used with children
  • Tube is inserted through nose and into stomach to obtain gastric secretions that may contain sputum

Slide 100: Bacteriologic Examination (8): Extrapulmonary TB

  • Specimens other than sputum may be obtained
  • Depends on part of body affected
  • For example:
    • Urine samples for TB disease of kidneys

Fluid samples from area around spine for TB meningitis

Slide 101: Bacteriologic Examination (9): Examination of AFB Smears

  • Specimens are smeared onto glass slide and stained
  • AFB are mycobacteria that remain stained after being washed in acid solution 

[IMAGE: AFB smear specimen]

Slide 102: Bacteriologic Examination (10): Examination of AFB Smears

  • Number of AFB on smear are counted
  • According to number of AFB seen, smears are classified as 4+, 3+, 2+, or 1+
    • For example, 4+ smear has 10 times as many AFB than 3+ smear
  • If very few AFB are seen, the smear is classified by the actual number of AFB seen

Slide 103:  Bacteriologic Examination (11): Examination of AFB Smears

  • Classification of Smear:
  • 4+:  Strongly positive; probably very infectious
  • 3+: Strongly positive; probably very infectious
  • 2+: Moderately positive; probably infectious
  • 1+ Moderately positive; probably infectious
  • Actual number of AFB seen (no plus sign): Weakly positive; probably infectious
  • No AFB seen: Negative; may not be infectious

Table 3.7 Smear Classifications and Results

Classification of Smear Smear Result Infectiousness of Patient
4+ Strongly positive Probably very infectious
3+ Strongly positive Probably very infectious
2+ Moderately positive Probably infectious
1+ Moderately positive Probably infectious
Actual number of AFB seen (no plus sign) Weakly positive Probably infectious
No AFB seen Negative May not be infectious*

* The criteria for determining whether a patient may be considered noninfectious are discussed in Module 5, Infectiousness and Infection Control.

Slide 104: Bacteriologic Examination Study Questions 3.30

  • What are the 4 ways to collect sputum specimens? Indicate which procedure is the least expensive and easiest to perform. (pg. 55)
    • Patient simply coughs up sputum and the sputum is collected in a sterile container.  This is the least expensive and easiest procedure.
    • Induced sputum
    • Bronchoscopy
    • Gastric washing

Slide 105: Bacteriologic Examination Study Question 3.31

  • What do laboratory personnel look for in a smear? (pg. 55)
    • Acid-fast bacilli (AFB)

Slide 106: Bacteriologic Examination Study Question 3.32

  • What does a positive smear indicate about a patient’s infectiousness? (pg. 55)
    • Patients who have any tubercle bacilli seen in their sputum have a positive smear.  Patients who have positive smears are considered infectious because they can cough tubercle bacilli into the air.

Slide 107 (Title Slide) Diagnosis of TB Disease: Medical Evaluation

5. Bacteriologic Examination

Slide 108: Bacteriologic Examination (12): Nucleic Acid Amplification Tests (NAA)

  • NAA tests directly identify M. tuberculosis from sputum specimens by:
    • Amplifying (copying) DNA and RNA segments
  • Can help guide clinician’s decision for patient therapy and isolation
  • Does not replace need for AFB smear, culture, or clinical judgment

Slide 109: Bacteriologic Examination (13): Nucleic Acid Amplification Tests (NAA)

  • If NAA test and AFB smears are positive:
    • Patients are presumed to have TB and should begin treatment
  • If NAA test is negative and AFB smears are positive:
    • Patients may have nontuberculous mycobacteria infection (NTM)

Slide 110: Bacteriologic Examination (14): Culturing and Identifying Specimen

  • Culturing:
    • Determines if specimen contains M. tuberculosis
    • Confirms diagnosis of TB disease
  • All specimens should be cultured

[IMAGE: Colonies of M. tuberculosis growing on solid media]

Slide 111: Bacteriologic Examination (15): Culturing and Identifying Specimen

  • Step 1: Detect growth of mycobacteria
    • Solid media: 3 - 6 weeks
    • Liquid media: 4 - 14 days
  • Step 2: Identify organism that has grown
    • Nucleic acid probes: 2 - 4 hours
    • Biochemical tests: 6 - 12 weeks

Slide 112: Bacteriologic Examination (16): Culturing and Identifying Specimen

  • Positive culture:  M. tuberculosis identified in patient’s culture
    • Called M. tuberculosis isolate
    • Confirms diagnosis of TB disease

Slide 113: Bacteriologic Examination (17): Culturing and Identifying Specimen

  • Negative culture:  M. tuberculosis NOT identified in patient’s culture
    • Does not rule out TB disease
    • Some patients with negative cultures are diagnosed with TB based on signs and symptoms

Slide 114: Bacteriologic Examination (18): Culturing and Identifying Specimen

  • Bacteriological examinations are important for assessing infectiousness and response to treatment
  • Specimens should be obtained monthly until 2 consecutive cultures are negative
  • Culture conversion is the most important objective measure of response to treatment

Slide 115: Bacteriologic Examination (19): Drug Susceptibility Testing

  • Conducted when patient is first found to have positive culture for TB
  • Determines which drugs kill tubercle bacilli
  • Tubercle bacilli killed by a particular drug are susceptible to that drug
  • Tubercle bacilli that grow in presence of a particular drug are resistant to that drug

Slide 116: Bacteriologic Examination (20): Drug Susceptibility Testing

  • Tests should be repeated if:
    • Patient has positive culture after 3 months of treatment; or
    • Patient does not get better

[IMAGE: Drug susceptibility testing on solid media]

Slide 117: Bacteriologic Examination (21): Types of Drug-Resistant TB

  • Mono-resistant: Resistant to any one TB treatment drug
  • Poly-resistant: Resistant to at least any two TB drugs (but not both isoniazid and rifampin)
  • Multidrug- resistant (MDR TB): Resistant to at least isoniazid and rifampin, the two best first-line TB treatment drugs
  • Extensively drug-resistant (XDR TB): Resistant to isoniazid and rifampin, PLUS resistant to any fluoroquinolone AND at least 1 of the 3 injectable second-line drugs (e.g., amikacin, kanamycin, or capreomycin)

Slide 118: Culture Specimen Study Question 3.33

  • Why is it necessary to culture a specimen? (pg. 65)
    • It is necessary to culture a specimen to determine whether the specimen contains M. tuberculosis and to confirm diagnosis of TB disease.

Slide 119: Culture Specimen Study Question 3.34

  • What does a positive culture for M. tuberculosis mean? How is this important for the TB diagnosis? (pg. 65)
    • It means that M. tuberculosis has been identified in a patient’s culture. A positive culture for M. tuberculosis confirms the diagnosis of TB disease.

Slide 120: Drug Susceptibility Study Question 3.35

  • Why are drug susceptibility tests done? (pg. 65)
    • To determine which drugs will kill the tubercle bacilli that are causing disease in a particular patient.  Test results can help clinicians choose the appropriate drugs for each patient.

Slide 121: Drug Susceptibility Study Question 3.36

  • How often should drug susceptibility tests be done? (pg. 65)
    • Should be done when the patient is first found to have a positive culture for M. tuberculosis
    • Tests should be repeated if a patient has a positive culture for M. tuberculosis after 3 months of treatment or if a patient is not getting better

Slide 122: (Title Slide) Reporting TB Cases

Slide 123: Reporting TB Cases

  • TB programs report TB cases to CDC using a standard case report form called the Report of Verified of Case of Tuberculosis (RVCT)
    • All cases that meet criteria are called verified TB cases

[IMAGE: First page of the RVCT form]

Slide 124: Criteria for Reporting TB Cases (1)

  • Cases that meet one of these four sets of criteria are counted as verified TB cases:
  • Patient has positive culture for M. tuberculosis
  • Patient has positive NAA test for M. tuberculosis
      • NAA test must be accompanied by culture for mycobacteria species

Slide 125: Criteria for Reporting TB Cases (2)

  • Patient has positive AFB smear, but culture has not or cannot be done
  • In the absence of laboratory confirmation, patient has:
      • Positive TST reaction
      • Other signs and symptoms of TB disease
      • Been treated with 2 or more TB drugs
      • Been given a complete diagnostic evaluation

Slide 126: Criteria for Reporting TB Cases (3)

  • Cases that do not meet any of these sets of criteria may be counted as a verified TB case if health care provider has decided to treat the patient for TB disease

Slide 127: (Title Slide) Case Studies

Slide 128: Module 3: Case Study 3.1

  • Which of the following patients have a positive TST reaction? Circle the best answer (s). (pg. 17)
    • Mr. West, 36 yrs. old, HIV infected, 8 mm induration (positive TST reaction)
    • Ms. Hernandez, 26 yrs. old, native of Mexico, 7 mm induration
    • Ms. Jones, 56 yrs. old, diabetic, 12 mm induration (positive TST reaction)
    • Mr. Sung, 79 yrs. old, nursing home resident, 11 mm induration (positive TST reaction)
    • Mr. Williams, 21 yrs. old, no known risk factors, 13 mm induration
    • Mr. Marcos, 42 yrs. old, chest x-rays findings suggestive of previous TB, 6 mm induration (positive TST reaction)
    • Ms. Rayle, 50 yrs. old, husband has pulmonary TB, 9 mm of induration (positive TST reaction)

Slide 129: Module 3: Case Study 3.2 (1)

  • A 30 year-old man who recently immigrated from India is given a TST and found to have 14mm of induration.  He reports that he was vaccinated with BCG as a child.  He also says that his wife was treated for pulmonary TB disease last year. (pg. 20)

Slide 130: Module 3: Case Study 3.2 (2)

  • How should this man’s results be interpreted?
    • Positive reaction to TST
    • Should be further evaluated for LTBI or TB disease
  • What factors make it more likely that this man’s positive reaction is due to TB infection?
    • From area of the world where TB is common
    • Wife had pulmonary TB

Slide 131: Module 3: Case Study 3.3 (1)

  • Mr. Bell comes to the TB clinic for a TST.  He believes that he has been exposed to TB, and he knows he is at high risk for TB because he is HIV infected.  He is given a TST, and his reaction is read 48 hours later as 0 mm of induration. (pg. 25)

Slide 132: Module 3: Case Study 3.3 (2)

  • What are 3 ways to interpret this result?
    • May not have TB infection
    • May be anergic
    • It may be less than 8–10 weeks since he was exposed to TB

Slide 133: Module 3: Case Study 3.4 (1)

  • Ms. Wilson is a 60 year-old nurse.  When she started a job at the local hospital, she was given a TST, her first test in 25 years.  Her reaction was read 48 hours later as 0 mm induration.  Six months later, she was retested as part of the TB testing program in the unit where she works.  Her skin test reaction was read 48 hours later as 11 mm of induration. (pg. 32)

Slide 134: Module 3: Case Study 3.4 (2)

  • What are 2 ways to interpret this result?
    • She was exposed to TB sometime in the 6 months between her first and second skin tests
    • Booster phenomenon

Slide 135: Module 3: Case Study 3.5 (1)

  • Mr. Lee has a cough and other symptoms of TB disease, and he is evaluated with a chest x-ray.  However, he is unable to cough up any sputum on his own for the bacteriologic examination. (pg. 52)

Slide 136: Module 3: Case Study 3.5 (2)

  • What should be done?
    • Other techniques can be used to obtain sputum.  First, clinicians can try to obtain an induced sputum sample.  If they cannot obtain the sample, a bronchoscopy or gastric washing may be done.

Slide 137: Module 3: Case Study 3.6 (1)

  • Ms. Thompson gave three sputum specimens, which were sent to the laboratory for smear examination and culture. The smear results were reported as 4+, 3+, and 4+. (pg. 56)

Slide 138: Module 3: Case Study 3.6 (2)

  • What do these results tell you about Ms. Thompson’s diagnosis and her infectiousness?
    • Results show that Ms. Thompson’s sputum specimens contain many acid-fast bacilli
    • Smears are positive, clinicians should suspect that she has TB disease and should consider her infectious
    • It is possible that the AFB are mycobacteria other than tubercle bacilli 
    • Diagnosis cannot be proven until culture results are available

Slide 139: Module 3: Case Study 3.7 (1)

  • Mr. Sagoo has symptoms of TB disease and a cavity on his chest x-ray, but all of his sputum smears are negative for acid-fast bacilli. (pg. 57)

Slide 140: Module 3: Case Study 3.7 (2)

  • Does this rule out the diagnosis of pulmonary TB disease?
    • No
  • Why or why not?
    • M. tuberculosis may grow in the cultures even though there were no acid-fast bacilli on the smear.  Mr. Sagoo’s symptoms and his abnormal chest x-ray suggest that he does have pulmonary TB disease.

Slide 141: Module 3: Case Study 3.8 (1)

  • In the public health clinic, you see a patient, Ms. Sanchez, who complains of weight loss, fever, and a cough of 4 weeks’ duration.  When questioned, she reports that she has been treated for TB disease in the past and that she occasionally injects heroin. (pg. 66)

Slide 142: Module 3: Case Study 3.8 (2)

  • What parts of Ms. Sanchez’s medical history lead you to suspect TB disease?
    • Symptoms of TB disease (weight loss, fever, persistent cough)
    • Past treatment for TB disease
    • History of injecting illegal drugs
  • What diagnostic tests should be done?
    • Chest x-ray
    • Sputum smear and culture
    • Drug susceptibility testing

 

 
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