Tuberculosis Parts III

Question 1

Risk factors that increase exposure to TB:

Answer 1

poor hygiene
poor ventilation
overcrowding
living in high previlence area.

Question 2

Risk factors that impair host immune response and ability to control any TB infection?

Answer 2

• HIV
• Malnutrition
• Medications that decrease immune system, e.g. Steroids

Question 3

transmission of TB

Answer 3

BY: airborne spread
inhalation of infectious aerosols.

Question 4

how is chest Xray diagnosis useful?

Answer 4

for secondary reactivation disease- may see cavity usually in upper lobes.

Primary complex may be seen in children- enlarged hilar or paratracheal nodes with or
without pulmonary infiltrate or nodule

Pleural effusion

Question 5

advantage of using microscopy for Acid-fast bacilli.

Answer 5

Advantages
* Simple
* Rapid (same day result)
* Inexpensive

Question 6

Disadvantage of Microscopy for Acid-fast bacilli

Answer 6

needs a lot bacilli to present to see them.
Doesn’t differentiate between different kinds of mycobacteria
Doesn’t differentiate between live or dead mycobacteria
* When used for follow up of patients on treatment

Question 7

Molecular diagnosis of TB

Answer 7

1.Based on detection of M. tuberculosis DNA
2.can also be used to detect known genes causing drug resistance.

Question 8

advantage of molecular tests:

Answer 8

Highly sensitive: can detect as few as 150 organisms/ml of sputum with latest version of GXP
* Directly from clinical specimens though can also be used on culture isolates
* Quick
* Can be done as point-of –care test though not always cost-effective then

Question 9

Disadvantages of molecular tests

Answer 9

Expensive
* Don’t distinguish alive from dead organisms, so not so good for patients recently treated for TB

Question 10

Tuberculin skin test (TST)

Answer 10

The test that Involves intradermal injection of tuberculin and measuring the amount of induration (palpable
swelling) that occurs 2-3 days later.

Note testing for delayed hypersensitivity response to this protein.

Question 11

what is tuberculin?

Answer 11

is a partially purified extract of M. tuberculosis protein.

Question 12

limitation of TST

Answer 12

can a false negative in severe immunosuppression, overwhelming TB infection

Can get false positive result after BCG vaccination or exposure to NTMs