Clinical Updates on Tuberculosis and STDsSeptember 30 – October 1, 2019Las Vegas, NV
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Joseph P. Iser, MD, DrPH, MSc
Chief Health Officer
There are two kinds of tests that are used
to determine if a person has been
infected with TB bacteria• The tuberculin skin test and
• TB blood tests (IGRAs)
These do not differentiate between latent
TB infection and active TB disease
They also do not predict who may
progress from latent to active disease
Clinical Updates on Tuberculosis and STDsSeptember 30 – October 1, 2019Las Vegas, NV
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Patient history and other tests are
needed to determine whether the person
has TB disease• Medical history
• Physical examination
• Test for TB infection
• Chest x-ray
• Appropriate laboratory testing (sputum
samples)
Those who have spent time with someone
with TB disease
People from countries where TB is
common
People who work or live in high-risk
settings
Healthcare workers exposed to TB
Some others
Clinical Updates on Tuberculosis and STDsSeptember 30 – October 1, 2019Las Vegas, NV
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People with HIV
Recently exposed
Young children
Injection drug users
Other immune deficiencies
Elderly
Inadequately treated people
Tuberculin Skin Test• Performed by injecting a small amount of fluid
(tuberculin) subcutaneously
• Person must return within 48-72 hours to read so requires 2 visits
• Look for raised hard area (induration) and measure size by ruler, compare to standards
• Redness makes no difference to reading
• Size of reaction is an estimate of risk for TB infection
• Preferred in children younger than 5
Clinical Updates on Tuberculosis and STDsSeptember 30 – October 1, 2019Las Vegas, NV
Materials Folder Link: http://bit.ly/2nP9ALF 4
Tuberculin Skin Test—Positive• Positive Skin Test means that the person’s body
was infected with TB bacteria
• Additional tests are required to determine
whether the infection is latent or active
Tuberculin Skin Test—Negative• This means the person’s body did not react
• TB infection or disease is not likely (with
exceptions)
TST preferred in young children
Clinical Updates on Tuberculosis and STDsSeptember 30 – October 1, 2019Las Vegas, NV
Materials Folder Link: http://bit.ly/2nP9ALF 5
Also called interferon-gamma release
assays (or IGRAs)
Measure how strong the immune system
reacts to TB bacteria by testing the
person’s blood in a laboratory
Two IGRA tests are approved by FDA and
available in the US• QFT Gold Plus (used by SNHD)
• T-SPOT TB Test (T-Spot)
Either requires only one visit
Measure a person’s immune reaction to
M tuberculosis
Clinical Updates on Tuberculosis and STDsSeptember 30 – October 1, 2019Las Vegas, NV
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Positive IGRA• Person has been infected with TB bacteria
• Does not differentiate between latent and active cases
• Additional tests are needed to determine whether the diagnosis is latent or active TB
• Treatment would be done by a HCW
Negative IGRA• The person’s blood did not react to the test
• Latent TB infection or active TB not likely
IGRAs are the preferred method of TB
infection testing for• People who have received bacille Calmette-
Guerin (BCG); BCG is a TB vaccine
• People who have a difficult time returning for a
second appointment to look for a reaction to the
TST
Clinical Updates on Tuberculosis and STDsSeptember 30 – October 1, 2019Las Vegas, NV
Materials Folder Link: http://bit.ly/2nP9ALF 7
IGRA interpretations based on the
amount or number of cells releasing IFN-
gamma
IGRAs are an aid to diagnosis
Indeterminate or borderline tests are just
that
Diagnosis requires medical evaluation
and epidemiological and historical
information
Generally NOT needed for people with a low risk of infection
Those at higher risk should be tested• People who have spent time with an active case
• People with immune deficiencies
• People with symptoms
• People from countries where TB is endemic
• People who live or work in congregate living situations
• People who use illicit drugs
Clinical Updates on Tuberculosis and STDsSeptember 30 – October 1, 2019Las Vegas, NV
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Many people born outside the US have
been vaccinated
They may receive a TST, but BCG may cause
a positive skin test when they have not been
exposed to TB bacteria (false-positive)
If positive TST, additional tests are needed
IGRAs are NOT affected by BCG vaccination
and should not have a false-positive result
Health care provider should choose
which test to use
Factors to consider include the reason for
testing, test availability, and cost
Costs for IGRAs can be ~$35 (QFT) to $55
(T-SPOT)
Generally, it is not recommended testing
a person with multiple types of tests
Clinical Updates on Tuberculosis and STDsSeptember 30 – October 1, 2019Las Vegas, NV
Materials Folder Link: http://bit.ly/2nP9ALF 9
Requires a single patient visit to conduct
the test
Results can be available within 24 hours
Does not boost responses measured by
subsequent tests
Prior BCG vaccination does not cause a
false-positive IGRA test result
Blood samples must be processed within 8-30 hours after collection while white blood cells are still viable
Errors in collecting or transporting blood specimens or in running and interpreting the assay can decrease the accuracy of IGRAs
Limited data on the use of IGRAs to predict who will progress to TB disease in the future
Clinical Updates on Tuberculosis and STDsSeptember 30 – October 1, 2019Las Vegas, NV
Materials Folder Link: http://bit.ly/2nP9ALF 10
There is limited data on the use of IGRAs
for• Children younger than 5 years of age
• Persons recently exposed to M tuberculosis
• Immunocompromised persons
• Serial testing
Tests are expensive
If infection is shown by a positive TB test,
other tests are needed to determine whether
the person has active TB
History, PE, and other tests have outline in
slides above
If the person does not have active disease
but only latent infection, treatment options
should be based on a person’s chances of
developing TB disease
Clinical Updates on Tuberculosis and STDsSeptember 30 – October 1, 2019Las Vegas, NV
Materials Folder Link: http://bit.ly/2nP9ALF 11
Increased risk for acquiring TB from
patients with unrecognized TB disease
Increased risk of transmission to
vulnerable/immunocompromised
patients
Annual testing is not recommended for
HCW not at high risk
Greater risk to pregnant women and
babies
TST valid and safe
IGRA valid and safe