Tuberculosis (and other mycobacterium) Flashcards
what are the 3 groups of mycobacteria?
M. leprae
M. tuberculosis
Non-tuberculosis mycobacteria (NTM)
What two factors have increased the extremity of M. tuberculosis?
Increase in HIV
Multi-drug resistant TB
How is TB acquired?
inhalation of tubercle bacterii infective droplets (less than 5 microns) reach the alveoli
What is the infectivity of TB related to?
Duration of exposure
Concentration of droplet nuclei in the air
What is a TB primary lesion?
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
Describe Lympho-hematogenous spread of TB
spread via the Ghon complex and Simon’s foci
Leads to foci at distant sites: bone, kidney, liver, spleen
What is the Ghon complex?
spread of TB to the regional hilar lymph nodes and localized pulmonary lesion
Hilar: depression where vessels enter an organ
What is the Simon’s foci
Spread of TB to the lung apices
Responsible for common apical cavitary disease
What is acute miliary tuberculosis?
Massive spread of TB throughout body
Describe delayed hypersensitivity
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”
Differentiate between active and inactive TB
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.
What are outcomes of the extrapulmonary lesions?
Often the hypersensitivity response can’t eradicate them .
Dormant lesions in the skeletal or renal are most common
Name the 4 diagnostic tests for TB
1) Radiologic findings
2) Interferon-gamma release assay
3) Tuberculin skin test (TST)
4) Acid fast bacilli (AFB) stain and culture
RITA
Describe the TST
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
Describe the Interferon-Gamma Release Assay
Used as a diagnostic for TB infection
Don’t differentiate between active or inactive TB
Describe radiologic findings of TB
X-rays: apical cavitary lesions in lungs
Calcification in renal parenchyma
Miliary TB can have other distinct patterns (vague info here)
Describe the acid fast bacilli stain and culture in relation to TB
Definitive diagnostic method
Multiple specimens necessary r/t small amount of organisms
Prevents the acid added to a smear from turning the organism colour
What are the clinical implications of a positive acid fast stain?
Can indicate large enough quantities of organism to make the person contagious
How long does it typically take a TB culture to become positive? What implications does this timeline have?
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
3 implications of drug resistant TB
increased morbidity
increased mortality
increased outbreaks
What are 4 more common NTMs?
Non-tuberculous mycobacteria:
- M. avium complex (MAC): mimics TB
- M. marinum (fish tank granuloma)
- M. ulcerans (buruli ulcer)
- M. fortuitum
What 3 factors can cause delayed detection of TB?
Lack of physician awareness
Atypical presentation
Delayed lab tests
LAD
What activities or procedures are higher risk for the spread of droplets?
Air:
coughing
AGMPs
Bronchoscopy
Tissue:
Morgue
surgical
Describe the ideal room requirements for someone with TB
Negative pressure to rest of hosp w/ external vent
6-12 room air changes/hour
UV or HEPA filter
What is BCG?
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.
How is multi-drug resistant TB defined?
Resistant to at least:
isoniazid and rifampin
Extensively drug resistant TB is resistant to what?
At least 4 drugs. Typically: isonizid rifampin fluoroquinolones at least one of the injectable second-line drugs (amikacin, capreomycin, kanamycin)
