Tuberculosis Flashcards
(54 cards)
True or false: tuberculosis is not curable
false
tuberculosis is preventable and curable
Which population is impacted by tuberculosis the most in Saskatchewan?
Indigenous
-6x higher than the provincial rates
-42% of cases in SK living in First Nations communities
Which organism causes tuberculosis?
mycobacterium tuberculosis
How is tuberculosis spread?
spread is airborne via coughing or sneezing
-host inhales droplet nuclei
-close contacts most likely to be infected
-prolonged contact: risk of infection can be up to 30%
Describe mycobacterium tuberculosis.
acid fast bacillus
-impervious to gram staining (can appear weakly gram +)
slow growing (doubling time 20hrs)
What are the risk factors for tuberculosis?
foreign born from highly endemic area
Canadian Indigenous population
close contact
homeless
incarceration
alcoholism, IVDU, malnutrition
co-infection with HIV (synergism)
What are the risk factors for active TB disease?
once infected with M. tuberculosis: lifetime risk of active TB is 10%
risk greatest during first 2 years after infection
<2yo and >65yo: greater risk of active disease
immunosuppression
HIV infected
What increases the probability of transmission of tuberculosis?
# of infectious droplets per volume of air and length of time spent breathing that air
bacterial burden in source
upper lung disease in source
laryngeal disease in source
severity and amount of cough in source
crowding and poor ventilation
duration of exposure
proximity to source
delayed diagnosis and tx of source
What is involved in the host response of a tuberculosis infection?
T-lymphocyte response (mainly CD4+)
-active macrophages that engulf and kill mycobacterium
TNF-a and TNF-y are important cytokines in coordinating immune response
organism has many mechanisms to evade immune response
How does a primary infection of tuberculosis occur?
inhalation of droplet nuclei which reach alveoli
What does the progression of clinical tuberculosis depend upon?
infecting dose (# of organisms inhaled)
virulence of the organism
cell-mediated immune response
-macrophages kill: infection controlled
-organism not killed: macrophages rupture, bacteria spill out
What occurs roughly 3 weeks after tuberculosis infection?
T-lymphocytes are presented with M. tuberculosis antigen
T-cells become active and secrete INF-Y
-this stimulates macrophages to become -cidal
large # of -cidal macrophages surround the tuberculosis foci
What is the process called for creating activated microbiocidal macrophages?
cell mediated immunity
What is occurring at the same time as CMI?
DTH (delayed-type hypersensitivity)
-cytotoxic immune response that kills nonactivated immature macrophages that allow bacillary replication
-occurs via T lymphocytes
-released bacteria then killed by activated macrophages
What can the inflammatory response to tuberculosis result in?
tissue necrosis
calcification
lymph node enlargement
When is the tuberculin skin test positive?
when activated lymphocytes reach an adequate number and tissue hypersensitivity results
Describe reactivation of disease for tuberculosis.
occurs in 10% of cases
most often in apices of lung (high O2, poor local immunity)
organisms within granulomas emerge and multiply extracellularly
granulomas liquefy and spread producing cavities
if untreated, destroy the lung - hypoxia, resp acidosis, death
What are extrapulmonary sites or diseases that can be caused by tuberculosis?
lymphatic and pleural disease most common
bone (often vertebrae), joint, GU, meningeal
large # of organisms in bloodstream (miliary TB)=emergency
HIV (destroys CD4+ cells = depleting cells that control TB)
What are the signs and symptoms of tuberculosis?
gradual onset
may not seek medical attention until hemoptysis
fever, cough, fatigue, night sweats, weight loss
Frank hemoptysis
chest exam: dullness to percussion, rales
moderate increase in WBC (mainly lymphocytes)
CXR: nodular infiltrates (apices), cavitations
How is tuberculosis diagnosed?
Mantoux test (TB skin test)
-read in 48-72h
-measure the induration (bump), not redness
sputum culture and sensitivity
In general, what is the treatment for tuberculosis?
isolation to prevent spread
drugs to cure
adherence: directly observed therapy (DOT)
identification of contacts
What is required for active tuberculosis?
combination therapy
Explain the differences in drug susceptibility within the 3 subpopulations of microorganisms.
extracellular:
-isoniazid, rifampin, streptomycin
within granulomas:
-pyrazinamide best drug
-isoniazid and rifampin
intracellular within macrophages:
-rifampin, isoniazid, quinolones
What is the treatment for latent tuberculosis?
rifampin daily x 4 months (4R)
-#1 option
rifapentine and isoniazid once weekly x 3 months (3HP)
unable to use rifamycin regimen:
-isoniazid daily x 9 months (6 month is alt)
