The TB Risk Assessment

VDH TB Control and Prevention Program2011

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

Persons at Risk for DevelopingTB 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:

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)

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

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

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

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

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.)

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

The Tuberculin Skin Test or TST

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

TST Result: False Positive

Possible causes Non-tuberculous mycobacteria 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

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

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

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

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

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)

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

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.

Interpretation of the TST: Persons Positive at > 15 mm

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

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

Interferon Gamma Release Assay –

the TB blood test or IGRA

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)

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

QuantiFERON TB Gold-in-TubeSample Results

T Spot Sample Result

Comparison of IGRA vs. TST

IGRA 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

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

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

?? Questions ??