Tuberculosis Flashcards
which places have the highest TB incidence?
Africa and Asia
People are primarily infected with TB through what?
inhalation (airborne particles 1-5 microns in size generated by individuals with pulmonary and laryngeal TB)
which TB is the most infectious?
laryngeal
describe the pathophysioloygy of TB
the infectious droplet can go to the alveoli, be phagocyted by macrophages (where MTB survive), produce local infection, and in some cases disseminate. Bacteria first spread to regional lymph nodes and are then disseminated.
True or false. During the initial infection, the individual is not contagious unless active disease develops?
True
how long does it take for immunity to develop?
10-12 weeks and further spread is prevented. Within 2-12 weeks the PPD skin test becomes positive, but infection may remain latent or progress to active TB.
Within 2 years of initial infection ___ of persons develop active disease
5%
True or false. If no disease develops within 2 years, the annual risk of reactivation is low (5-10%)?
True
describe the primary TB infection
-asymptomatic with sometimes fevers, cough, or erythema nodosum (skin inflammation located in the fatty layer of skin. Reddish, painful lumps most commonly in front of the legs below the knees dime to quarter size).
-Gohn complex (infiltrate and lymphadenopathy on draining lymph nodes), miliary pattern in progressive cases
-disseminatoin can be controlled but multiple non pulmonary sites of controlled infection can be established and lead to extrapulmonary disease during postprimary TB reactivation
TB is an ____ pathogens
intracellular (lives inside macrophages)
what is caseous necrosis?
a form of cell death where the tissue maintains a cheese-like appearance. The host destroys its own tissue to control the uninhibited multiplication of bacilli that would otherwise be fatal. Integral part of host defenses. Majority of tubercle bacilli are killed, while some survive extracellularly in sold caseous material but can’t multiply because of anoxic conditions and presence of enzymes from dead cells.
How does post primary TB manifest?
productive cough, fever, night sweats.
Infiltrates on the upper lobes or superior segments of lower lobes. Cavitation on x-rays.
Cough is initially nonproductive but becomes sputum productive as tissue necrosis progresses.
what are some screening tools for TB?
country of origin, past exposure
pulmonary TB may be associated with what?
hemoptysis (small amounts of superficial erosion to airway or massive amounts if it is the result of rupture of a dilated vessel of the pulmonary cavity, known as Rasmussen aneurysm).
how does postprimary TB differ in HIV patients?
-higher CD4 T-cell counts, atypical with a miliary pattern, lower lobe infiltrates, or normal chest x-rays
MTB is a gram __ ____
positive bacillus; aerobic
what are some other organisms that can stain by acid-fast?
-leprosy
-nicardia
-rhodococcus
-legionella micdadei
which test is required for definitive TB diagnosis?
AFB culture (allows susceptibility to be done too)
which tests can be used for rapid, but not definitive, TB diagnosis?
-two NAATs
-DNA probe and PCR tests
True or false. The TST is used to detect people with latent TBI and cannot be used for ruling in or out active TB
True. This is because a positive TST merely indicates a history of LTBI at some point, it conveys no information regarding the persons current infection status (which may have been cured previously). Also, a TST may be negative even when a person has active disease.
describe mantoux testing
-5 tuberculin units are injected intradermally on the volar (palmar) surface of the forearm; may be placed on the dorsal surface if necessary. Wheel at injection site.
-read 48-72 hours after placement. Positive test is determined by the number of millimeters in duration caused.
When is a TB test considered positive?
increase induration of 10mm compared to be previous test
In what groups of >5mm induration a positive test?
-HIV persons
-recent contacts of a TB case
-fibrotic changes on CXR consistent with old TB
-patients with organ transplants and immunosupressed (>15 mg/day prednisone for 1 month)
when is >15mm a positive for TB?
persons with no TB risk factors
