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Block G -- Infection > Dr. Behr -- Tuberculosis > Flashcards

Dr. Behr -- Tuberculosis Flashcards

1
Q

Define tuberculosis

A

The diseased state:

  • Actively replicating bacteria
  • Contagious, culture positive
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2
Q

Define tuberculous infection

A

The carrier state

  • Clinically latent (latent TB infection/LTBI)
  • Non-infectious, tuberculin positive
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3
Q

Bacteria responsible for tuberculosis and tuberculous infection

A

Mycobacterium tuberculosis

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4
Q

Cause of avian TB

A

Mycobacterium avium

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5
Q

Hypothesized cause of Crohn’s disease

A

M. avium paratuberculosis

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6
Q

Environmental bacterium that causes TB-like disease in miners with silicosis

A

M. kansasil

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7
Q

Cause of leprosy

A

M. leprae

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8
Q

Place of origin of M. tuberculosis and its geographic journey (4)

A
  1. Africa
  2. Paleo-migration –> Europe (by foot)
  3. Colonization of Americas (by ship)
  4. Fur trade = All across Canada (by canoe)
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9
Q

What kind of organism is M. tuberculosis (i.e. its behavior with humans)

A
  • Pathogen
  • Symbiont
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10
Q

How is *M. tb *an educated pathogen?

A
  • Localized, chronic pathology = ambulatory host and transmission
  • (As opposed to organisms such as Legionella pneumonia, which is a diffuse, fast disease with a very sick host and no transmission)
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11
Q

3 potential outcomes after TB exposure and their respective frequencies

A
  1. No infection
    • `(?; 2/3 don’t test +)
  2. Infection, no disease
    • (90% if immune status OK)
  3. Infection, disease +/- death
    • 5% in 2 years
    • 5% in rest of life
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12
Q

3 reasons why a few progress to TB

A
  • Age (infants)
  • Acquired immune deficiency
    • HIV+, steroids, Anti-TNF
  • Natural immunity
    • Genetics: people who progressed 1st time and are cured = 5x higher rate of TB than community
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13
Q

Where *M. tuberculosis *ends up in the human body

A

Alveoli of lungs (in alveolar macrophages)

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14
Q

2 options for the outcome of *M. tb *in alveolar macrophages

A
  1. Kill bacteria on contact –> no infection, tuberculin -
  2. Permit bacterial infectoin (Ghon focus)
    • Infection
    • TB positive
    • Attraction of other cells to aggregate –> granuloma
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15
Q

3 components of a granuloma

A
  1. Macrophages
  2. Lymphocytes
  3. Fibrous ring
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16
Q

How does *M. tb *end up in hilar lymph nodes?

A

Dendritic cells via lymphatics

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17
Q

2 options for the outcome of *M. tb *in hilar lymph nodes

A
  1. Chronic localized lymphadenitis
  2. Further spread
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18
Q

2 ways that TB can further spread if in hilar lymph nodes

A
  1. Up lymphatics via thoracic ducts –> hematogenous seeding
  2. Through lymphatics, within lungs –> areas of lowest vacular perfusion (apex)
19
Q

Non-transmissible TB

A

TB meningitis

20
Q

M. tb reservoir host

A

Human (rarely from animals)

21
Q

% of world’s population infected by M. tb

A

1/3

22
Q

Cause of death in ~25% of AIDS

A

TB

23
Q

Strongest risk factor for progression of TB infection to disease

A

HIV infection

24
Q

4 general clinical manifestations of TB

A
  1. Fever
  2. Sweats
  3. Weight loss
  4. “Consumption”
25
Q

2 contagious organ specific clinical manifestations of TB

A

Pulmonary

  • Cough
  • Sputum +/- blood
26
Q

5 organ-specific non-contagious clinical manifestations of TB

A
  1. Scrofula = swollen lymph nodes
  2. Genitourinary = sterile pyuria
  3. Bone = back pain, fracture, “hump-back”
  4. Meningitis = headache, obtundation
  5. Miliary TB (no obvious site)
27
Q

Number of sputum specimens for smear exam and culture

A

3

28
Q

3 things to do if patient is unable to cough up sputum

A
  • Induce sputum (kids too)
  • Bronchoscopy
  • Gastric aspiration
29
Q

Positive AFB smear

A

Red rods = tubercle bacilli

30
Q

Purpose of cultures in TB diagnosis and how long results take

A
  • Confirmation
  • 2 - 3 weeks
31
Q

Compare PCR sensitivity to other forms of TB diagnosis

A
  • Better than microscopy
  • Not as good as culture
32
Q

2 situations where PCR use is appropriate in TB diagnosis

A
  1. AFB smear + and want quick answer to what bacteria is present
  2. New, rapid test by Cepheid for developing world (including Nunavik)
33
Q

2 situations where PCR has limited utility in TB diagnosis

A
  1. AFB smear negative
  2. Non-pulmonary sample
34
Q

Length of short course treatment for TB

A

24 weeks

35
Q

3 points for prioritizing TB control

A
  1. Identify and treat active TB to reduce # of contagious persons
  2. Identify contacts of cases, test for infection, provide chemoprophylaxis
  3. Identify people with patent infection as potential candidates for chemoRx
36
Q

2 possible causes of a false-positive PPD

A
  1. Nontuberculous mycobacteria
  2. BCG vaccination
37
Q

5 possible causes of false-negative PPD

A
  1. Anergy
  2. Recent TB infection
  3. Very young age (<6 months old)
  4. Live-virus vaccination
  5. Overwhelming TB disease
38
Q

New test for TB detection

A

IFN-gamma release assays

39
Q

Platform of IFN-gamma release assays

A

From skin to lab ELISA

40
Q

Advantage of IFN-gamma release assays

A

Specificity in face of BCG vaccination

41
Q

Disadvantage of IFN-gamma release assays

A

Poor reproducibility

42
Q

LTBI treatment

A

Isoniazid for 9 months

43
Q

Efficacy of BCG vaccination against peditric TB

A

80%

Block G -- Infection (23 decks)

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