Flashcards in Tuberculosis Deck (29):
What areas of world have highest rates of TB?
Subsaharan Africa and Asia
What caused increase in TB in US in 1980's? (5 things)
HIV, Asian immigration, increased homelessness, decreased public health spending, increased drug resistance.
What organisms causes TB?
2 main virulence factors
Obligate aerobic, preferring high O2 levels.
Transmitted via small droplet aerosols
Virulence factors: 1) being able to multiply in macrophages. 2) my colic acid forms waxy coating on cell wall, preventing phagosome-lysosome interactions and oxidative killing.
Humans are only natural reservoir
Surface glycolipid on M tb that triggers Th1 response and enhances survival w/in macrophages.
Steps of intracellular invasion
1) Taken up by mannose / complement receptors on macrophages.
2) Prevents fusion w/ lysozyme and inhibits ROS damage.
3) Prevents apoptosis of host cell.
4) Blocks IFNg receptor to prevent intracellular killing.
5) TNF release attracts more macrophages --> increased spread. TNF also causes systemic sxs (fever, aches)
6) Infected macrophages may travel to lymph nodes --> bacteremia --> infection of other organs.
When is CMI response initiated?
What specific type of response is it?
CMI initiated when 1000-10000 cells accumulate.
Delayed-type hypersensitivity (type IV)
What percentage of people exposed to TB become infected?
Of those infected, what percentage have active disease?
What percentage have sxs in first 2 years, compared to later?
10-30% of people exposed get infected.
Only 10% of those infected have active disease.
5% develop sxs in 1st 2 years. 5% later.
What is #1 killer of pxs w/ HIV?
Disseminated / Miliary TB
What is it?
Serious form that spreads through blood to multiple body sites.
Most common in young kids and HIV pxs.
What does it stand for?
What is it?
Immune Reconstitution Inflammatory Syndrome
Occurs in HIV pxs when CD4 cells reactivate w/ tx --> pathological inflammation.
Mycobacterium Avian Complex (MAC)
Bird disease that infects HIV pxs
Infected TB pxs w/ increased risk of sxs
HIV, diabetes, CKD, silicosis, immunosuppression, less than 4 y/o
Sxs of TB (5 things)
Chronic cough, fevers, night sweats, weight loss, anorexia. More common in parts of lung w/ low perfusion and high ventilation (upper lobes).
TB skin test
What is injected?
What type of rxn is it?
2 parts of biphasic response
Cytokines that trigger erythema
Highest risk pxs and size of induration
Causes of false negatives
Causes of false positives
Purified protein derivative (PPD)
Delayed type hypersensitivity rxns (type IV)
Biphasic: non-specific rxn early. Specific rxn (Th1 mediated) w/in 48-72 hrs.
IFNg and TNF --> capillary leak --> erythema and induration
Highest risk pxs: HIV, recent contact w/ active TB px, fibrotic changes on CXR, chronic prednisone use, and organ transplant
False neg due to immunocompromised pxs, booster phenomenon, and IL-10 effect.
False pos due to endemic NTM and prior BCG vaccination
What dose it stand for?
How does it work?
IFNg Release Assays
Expose T cells to TB in vitro. If T cells were previously primed, they release a ton of IFNg.
What is required to diagnose TB?
What is not sufficient to rule out TB?
Need positive sputum smear or biopsy.
TST, IGRA, and negative CXR in HIV pxs cannot rule out TB.
What can be used to speed up culture detection from 7 weeks to 1 week?
What should you do before starting tx for TB?
Assess for active disease (isolate them)
Do CXR (isolate and get sputum sample if positive.
Assume pxs w/ chronic respiratory sxs have active TB until ruled out.
Consider extrapulmonary TB
Why should you treat latent TB?
Are pxs contagious?
Decreases risk of progression to active disease by 70%
Tx for 9 months
How long does it take to not be contagious anymore after starting tx for active disease?
Risk of isoniazid
What is forbidden while on this drug?
Hepatotoxicity seen in elderly, pregnant women, and postpartum women.
Do NOT drink alcohol.
4 1st line drugs
Isoniazid, rifampin, ethambutol, and pyrazinamide
Either isoniazid or rifampin.
Isoniazid more common.
Multi-drug resistant TB
Risks for MDR TB
Both isoniazid and rifampin
Risks for MDR: prior therapy, foreign born, HIV, cavitary TB
Extensively drug resistant TB
All 1st line, 1 FQ, and at least 1 injectable 2nd line.
Types of resistance testing
Biochemical - most accurate but takes weeks
Molecular - done directly on cultures w/in 1-2 days.
What is it?
What's it derived from?
How does it work?
From Mycobacterium bovis
Does not prevent infection, but induces more rapid response by macrophages to prevent bacteremia.
Live vaccine so contraindicated in pregnancy and immunocompromised pxs.
What organism causes leprosy?
What is leprosy?
Leprosy is a chronic granulomatous disease of the peripheral nerves and superficial tissues.