TB and NTM Flashcards
how is TB spread? where does it land initially?
by carriers with ACTIVE disease via airborne droplet nuclei. Lands in mid or lower lungs. Hilar or mediastinal adenopathy
Where does TB most commonly spread? how does it spread?
Lymph nodes, vertebrae, meninges. hematogenously or via macrophages in lymph
What does the immune response to TB involve?
Activated lymphocytes but no antibodies. Caseating or noncaseating granulomas.
When does tissue hypersensitivity develop?
3-9 wks after infection
What are epithelioid and Langhans giant cells?
Epithelioid-highly stimulated macrophages
Langhans-fused macrophages (multiple peripheral nuclei)
What is the rate of reactivation infection?
5% w/in first two years, additional 5% after that. Higher in AIDS pts
How are primary TB infections characterized?
Majority-PPD +. Minority-primary (Ghon) comple. Necrosis and calcification of initial focus. Rarely-progressive Tb (in children,AIDS)
Where are bacteria harbored during latent TB infection?
w/in macrophages in the granuloma
What are the three main TB test?
PPD (TST), Interferon Gamma. Second has higher sens and spec but is more expensive
Where does TB usually reactivate?
Apical posterior lung (usually no hilar adenopathy). Extrapulmonary. Miliary.
Miliary TB
represents widespread dissemination of disease. Presents on CXR as reticulonodular infiltrates
What is the formula for tuberculous meningitis?
Pleocytosis (esp lymphocytic), high protein, low glucose, negative cultures
What is the fastest way to culture TB? Other ways?
Broth (1-3 wks). Solid media takes 3-8 wks. Fastest is Xpert MTB/RIF use nucleic acid amplification (same day) also test RIF resistance
What is the probability of resistance to a regimen?
the product of the probabilities of a resistant strain being present
What defines MDR-TB? XDR-TB?
Resistance to RIf/INH. Rif/INH plus fluoroquinolones and other second lines
