Tuberculosis (and other mycobacterium)

Question 1

what are the 3 groups of mycobacteria?

Answer 1

M. leprae
M. tuberculosis
Non-tuberculosis mycobacteria (NTM)

Question 2

What two factors have increased the extremity of M. tuberculosis?

Answer 2

Increase in HIV

Multi-drug resistant TB

Question 3

How is TB acquired?

Answer 3

inhalation of tubercle bacterii
infective droplets (less than 5 microns) reach the alveoli

Question 4

What is the infectivity of TB related to?

Answer 4

Duration of exposure

Concentration of droplet nuclei in the air

Question 5

What is a TB primary lesion?

Answer 5

Once the TB bacteria reaches the lung it is phagocytosed by a macrophage
The organism will survive this and multiplies intracellularly
Lesion develops consisting of the organism, acute & chronic inflammatory cells

Question 6

Describe Lympho-hematogenous spread of TB

Answer 6

spread via the Ghon complex and Simon’s foci

Leads to foci at distant sites: bone, kidney, liver, spleen

Question 7

What is the Ghon complex?

Answer 7

spread of TB to the regional hilar lymph nodes and localized pulmonary lesion

Hilar: depression where vessels enter an organ

Question 8

What is the Simon’s foci

Answer 8

Spread of TB to the lung apices

Responsible for common apical cavitary disease

Question 9

What is acute miliary tuberculosis?

Answer 9

Massive spread of TB throughout body

Question 10

Describe delayed hypersensitivity

Answer 10

Occurs 4-8weeks after exposure
Demonstrated by a positive TST
This means that the body now has the ability to kill the organism (using sensitized mononuclear cells)
Causes death of organism and surrounding tissue cells - therefore leads to area of necrosis
Pathophysiologically seen as “caseating granuloma”

Question 11

Differentiate between active and inactive TB

Answer 11

Active: progressive pulmonary TB with cavitation; at risk of spreading; need airborne precautions

Inactive: organisms persist in a dormant state for potentially several years (especially at lung apices, Simon’s foci). Not contagious

Inactive TB can return to active (back to lymphohematogenous stage), typically during decline in host immune status.

Question 12

What are outcomes of the extrapulmonary lesions?

Answer 12

Often the hypersensitivity response can’t eradicate them .

Dormant lesions in the skeletal or renal are most common

Question 13

Name the 4 diagnostic tests for TB

Answer 13

1) Radiologic findings
2) Interferon-gamma release assay
3) Tuberculin skin test (TST)
4) Acid fast bacilli (AFB) stain and culture

RITA

Question 14

Describe the TST

Answer 14

Tuberculin Skin Test

Indicates whether someone has developed a delayed hypersensitivity reaction to TB antigens.
Positive test indicates there has been exposure in the past to a mycobacteria
NTM may produce small positive result

Question 15

Describe the Interferon-Gamma Release Assay

Answer 15

Used as a diagnostic for TB infection

Don’t differentiate between active or inactive TB

Question 16

Describe radiologic findings of TB

Answer 16

X-rays: apical cavitary lesions in lungs
Calcification in renal parenchyma
Miliary TB can have other distinct patterns (vague info here)

Question 17

Describe the acid fast bacilli stain and culture in relation to TB

Answer 17

Definitive diagnostic method
Multiple specimens necessary r/t small amount of organisms
Prevents the acid added to a smear from turning the organism colour

Question 18

What are the clinical implications of a positive acid fast stain?

Answer 18

Can indicate large enough quantities of organism to make the person contagious

Question 19

How long does it typically take a TB culture to become positive? What implications does this timeline have?

Answer 19

10 days to 8 weeks

In the meantime TB can’t be separated from NTM based on smear appearance
Can cause increased transmission and increase time to receive drug sensitivities

Question 20

3 implications of drug resistant TB

Answer 20

increased morbidity
increased mortality
increased outbreaks

Question 21

What are 4 more common NTMs?

Answer 21

Non-tuberculous mycobacteria:

• M. avium complex (MAC): mimics TB
• M. marinum (fish tank granuloma)
• M. ulcerans (buruli ulcer)
• M. fortuitum

Question 22

What 3 factors can cause delayed detection of TB?

Answer 22

Lack of physician awareness
Atypical presentation
Delayed lab tests

LAD

Question 23

What activities or procedures are higher risk for the spread of droplets?

Answer 23

Air:
coughing
AGMPs
Bronchoscopy

Tissue:
Morgue
surgical

Question 24

Describe the ideal room requirements for someone with TB

Answer 24

Negative pressure to rest of hosp w/ external vent
6-12 room air changes/hour
UV or HEPA filter

Question 25

What is BCG?

Answer 25

Bacille Calmette Guerin
Vaccine for tuberculosis
Primarily used in countries with high rates of TB to prevent childhood illness
May interfere with TST depending on time of vaccine and age of pt.

Question 26

How is multi-drug resistant TB defined?

Answer 26

Resistant to at least:

isoniazid and rifampin

Question 27

Extensively drug resistant TB is resistant to what?

Answer 27

At least 4 drugs. Typically:
isonizid
rifampin
fluoroquinolones
at least one of the injectable second-line drugs (amikacin, capreomycin, kanamycin)