Tuberculosis PBL

Question 1

Describe what a positive TB PPD test is? (size of induration of purified protein derivative test)

Answer 1

1mm injected subdermally - sensitized TH1 helper cells recruit macrophages - Type IV hypersensitivity reaction causes induration/erythema after 48-72 hrs

If the induration is greater than 5mm in an HIV/immunocompramised patient it is positive

Induration greater than 10mm in IV drug users, HEALTH CARE WORKERS, increased risk, under 4 y/o it is positive

Induration greater than 15mm in normal healthy adults is positive

Note: Does not matter if the person has had the vaccination or not. Positive means positive result.

Question 2

Latent vs Active Tuburculosis

Answer 2

Active: Have symptoms* Cough, hemoptysis, abnormal CXR etc
-Primary
-Secondary
CONTAGIOUS - must isolate

Latent: does not have symptoms and does have a positive PPD test. Treat with INH for 9 months. No recommendation for CXR screening.
Not Contagious - no need for isolation

Question 3

What is MDR? What is is used for?

Answer 3

Surgical Resection of TB nodule

Question 4

Why do you have to treat so long for TB?

Answer 4

It is a slow grower.
They exist intracellularly and extracellularily
Where does streptomycin work? Inside the cells. Not extracellularily

Question 5

BCH vaccine

Answer 5

Tuberculosis vaccine

Used in countries with endemic TB but NOT the US. May cause a false positive PPD test