TB- Worldwide Control, Testing

Question 1

Primary tuberculous infection is caused by _________.

Answer 1

Mycobacterium tuberculosis (MTB)

Question 2

T or F. most people with MTB do not develop active disease.

Answer 2

True.

Question 3

What is the disease course for people exposed to TB?

Answer 3

TB Exposure–>either not infected or develop a primary tuberculous infection.

From a primary tuberculous infection any one of these can happen:

1. the infection is cleared spontaneously
2. It develops into a latent tuberculous infection (people often get reactivation TB from these)
3. It develops into progressive primary TB (this occurs in HIV patients and infants)

Question 4

What is LTBI?

Answer 4

latent tuberculosis infection. In LTBI the individual is infected with MTB but has no active disease. In immunocompetent individuals most primary infections do not develop into active disease but continue to harbor it in the latent form

Question 5

What are the major differences between LTBI and active TB in the lungs?

Answer 5

• LTBI has normal CXR while active TB does not
• It also has a normal (or negative) sputum smear and culture while active TB does not (test is positive)
• LTBI is asymptomatic and non-infectious while active TB is symptomatic and infectious.

Note: both will be skin test positive and both are caused by MTB

Question 6

Which patient group is TST positive with an induration of >5mm?

This is also the criteria of who should be tested for LTBI

Answer 6

Those with:

• recent close contact to an active case of TB
• HIV (this is the big one)
• apical fibronodular disease consistent with old healed TB
• organ transplants (immunocompromised)
• Anti-TNF therapy

Question 7

Which patient group is TST positive with an induration of >10mm?

This is also the criteria of who should be tested for LTBI

Answer 7

Those with:

• recent tuberculin skin test conversion (negative to positive recently)
• immigrants from TB prevalent regions
• high risk groups such as the homeless
• medical conditions such as diabetes and dialysis

Question 8

Which patient group is TST positive with an induration of >15mm?

This is also the criteria of who should be tested for LTBI

Answer 8

those who:

are otherwise healthy don’t have the risk factors mentioned in the previous groups

Question 9

What is a major way that false-positivity can occur with the TST (tuberculin skin test)?

what about false negatives?

Answer 9

false pos.- cross reaction in individuals who have recently received BCG vaccine.

Note: there can also be false positives in individuals with environmental mycobacteria

false neg.- in immunocompromised patients (AIDS, organ transplants, etc)

Question 10

How do you tell BCG vaccine scar from a smallpox scar?

Answer 10

BCG scar is raised

smallpox scar is indented

Question 11

What are the advantages of using an IGRA (either quantiferon or T- spot) over the traditional TST?

Answer 11

note: IGRA is interferon gamma releasing agent

These tests are more sensitive and specific. They do not exhibit cross reaction with BCG vaccinated individuals.

Question 12

Whats a more natural treatment for TB?

Answer 12

vitamin D.

Vitamin D3 specifically suppresses growth of MTB in macrophages.

Question 13

Treatment for LTBI? Which is preferred?

Answer 13

• 9 mo isoniazid (daily or BIW)
• 4 mo Rifampin (daily)
• 3 mo INH + rifampin (daily)

Rifampin is probably the best though because it has fewer serious adverse side effects, better adherence, and more cost effective than 9 mo of INH

Question 14

Summary

• A substantial portion of active TB cases are due to ___________.
• LTBI is diagnosed by either the _____ or the ______.
• Look for LTBI in subjects at risk for TB infection, for example _________.

Answer 14

• reactivation disease (derived from the large pool of individuals with LTBI)
• TST or IFNgamma- release assay
• patients with absolute or relative immunodeficiency, select health care workers (eg exposed to TB patients), and recent contacts of active TB cases

Question 15

T or F
A 50 y.o. man with a heart transplant is found to have a PPD of 8 mm. He has never received treatment for LTBI. He should be started on INH for a total of 9 months.

Answer 15

True: a solid organ transplant recipient is highly immunosuppressed and should receive INH for LTBI if the PPD is ≥ 5 mm.

Question 16

2. A 27 y.o. medical student beginning her 3rd year clinical clerkship has a PPD induration of 7 mm. She has no medical problems. She should get 9 months of INH prophylaxis because she will be constantly exposed to patients with TB.

Answer 16

False: for a health care worker who is otherwise healthy, the criteria for positivity is ≥ 10 mm. As for certain health care workers with patient contact, she should be tested yearly to monitor for PPD conversion.

Question 17

3. A 55 y.o. alcoholic man has a PPD induration of 15 mm. He lives in a homeless shelter in NYC and has been incarcerated recently. He is coughing up sputum that is blood streaked. His CXR shows an upper lobe cavitary lesion that is new from 1 year ago. His sputum smear is positive for AFB but the culture at 1 week is negative. He should receive INH for 9 months.

Answer 17

False: this man likely has active TB and should be treated with a multi-drug regimen (with at least 4 drugs).

Question 18

4. A 45 y.o. woman with schizophrenia has a PPD induration of 16 mm. She is otherwise healthy. Due to her history of non-adherence to her medications, you should prescribe 2 months of rifampin-pyrazinamide regimen rather than the 9 months of INH.

Answer 18

False: rifampin-pyrazinamide combination for LTBI is associated with an unacceptable risk of severe hepatitis and although a 2 month regimen is easier to adhere to, this regimen should (never) be used.

(this was not really talked about and will not likely be on the test)

Question 19

(may be more than one)

5. In a BCG-vaccinated person, the IFNγ-release assays (Quantiferon® or T-SPOT.TB®)…

a. are more specific than the TST.
b. are less specific than the TST.
c. have a better positive predictive value than the TST.
d. have a worse positive predictive value than the TST.

Answer 19

a and c

Question 20

possible side effects of isoniazid?

Answer 20

can cause hepatitis in those that drink alcohol and use drugs

Question 21

T or F MTB is picked up from the environment.

Answer 21

F. It is acquired from one person to another, through the respiratory tract.