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BLOCK B - RESPIRATION > Tuberculosis and non-tuberculous mycobacterium > Flashcards

Tuberculosis and non-tuberculous mycobacterium Flashcards

1
Q

What is tuberculosis?

A

A contagious infectious disease caused by the bacterium Mycobacterium tuberculosis (MTB).

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2
Q

What is latent tuberculosis?

A

When a person is infected with Mycobacterium tuberculosis (MTB), but the bacteria remain in an inactive, dormant state within the body.

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3
Q

How is Mycobacterium tuberculosis transmitted?

A

It is transmitted by airborne route exclusively, especially to people in close proximity to the affected individual

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4
Q

How does age influence the presentation of tuberculosis?

A

TB is more severe in younger children.
Infants and young children are more susceptible to developing severe forms of TB, and to have progression of the disease.

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5
Q

Name some key features of the Mycobacterium tuberculosis (4)

A
  • Shape: aerobic, slightly curved non-motile rod
  • Grows best in high oxygen tension, but can survive in adverse conditions for a long time in a dormant state
  • Very thick waxy outer layer which protects it and gives acid fast property
  • Only known host is human
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6
Q

What is the probability of transmission of MTB?

A

It is the probability of inhaling a viable bacterium, which is proportional to the concentration of the bacterium in air.

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7
Q

What is the probability of MTB transmission in a small room vs a big room?

A

Small room
* greater concentration
* greater probability of transmission

Big room
* smaller concentration
* smaller probability of transmission

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8
Q

How can MTB be eliminated from the environment?

A
  • MTB can be killed by sunlight or drying
  • Ventilation can remove airborne bacteria
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9
Q

What are markers of TB contagiousness?

A

Cavities on chest X-ray and positive acid-fast smear

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10
Q

What are the two possible results of exposure to MTB?

A

Either new infection or no infection.

This is determined by innate immunity - mechanism poorly understood

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11
Q

Define primary infection

A

When exposure results in new infection

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12
Q

How does the initial (innate) immune response respond to TB.

A

It is largely ineffective

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13
Q

What is our body’s primary defence mechanism for MTB?

A

Cell-mediated immunity: Special immune cells form a hard shell called granuloma around the MTB to contain the infection.

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14
Q

Following primary infection, cell-mediated immunity (CMI) determines…

A

Whether the disease develops or the infection becomes dormant.

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15
Q

CMI can be defective in… (4)

A
  • the very young and very old
  • patients with HIV infection
  • patient with other immuno-compromising conditions
  • patients with co-morbidities (diabetes, renal failure)
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16
Q

Development of effective CMI occurs by weeks 4-7 after infection. What happens if CMI is defective?

A

Primary TB infection is not controlled and symptomatic disease develops within 3-6 months.

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17
Q

What is disseminated TB or TB meningitis?

A

Severe, life-threatening forms of TB.

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18
Q

Who is most likely to develop more severe forms of TB, including disseminated TB or TB meningitis?

A

Very young children

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19
Q

If CMI is effective, what happens to TB?

A

It enters a latent or dormant state, because the TB bacteria are contained within granulomas.

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20
Q

Explain why the latent state of TB is a dynamic state.

A

The latent state results from homeostasis between MTB constantly trying to “escape” the granulomas and host defences constantly trying to “hold them back”. This is an active immune process.

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21
Q

How long can dormant TB bacteria remain viable?

A

40 years or more!

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22
Q

What are some clinical test features of latent TB? (4)

A
  • patient is asymptomatic
  • interferon gamma release assay is positive
  • tuberculin skin test is positive (5mm+)
  • chest X-ray is normal
23
Q

In 5-10% of cases of latent infection, active TB develops at some point. What are some risk factors for this? (6)

A
  • interval since infection
  • uncontrolled HIV/AIDS
  • age (infants and young children, elderly)
  • smoking, alcohol use
  • malnourishment (underweight)
  • diabetes (renal failure and silicosis)
24
Q

When is the highest risk for an active infection to develop from latent TB?

A

Within the first 1-2 years after infection

25
Q

What is the strongest known risk factor for latent TB to develop into active infection?

A

Uncontrolled HIV/AIDS

26
Q

What are some clinical features (symptoms) of TB?

A
  • Cough, sputum
  • Fever and night sweats
  • Hemoptysis (coughing up blood)
27
Q

What are some physical exam features of TB?

A

Chest exam usually normal
Individual may be thin

28
Q

What is the first step in diagnosing TB?

A

Chest X-ray: very sensitive (good at ruling out), but not very specific (a lot of false positives because of scarring)

29
Q

After CXR, how do we diagnose TB? (3 tests)

A

TB is diagnosed using microbiology testing.

Microscopic exam of sputum smear, stained for acid fast bacilli
* at least 3 samples of sputum
* rapid but not sensitive

Cultures (most specific and most sensitive - gold standard test)
* however, takes a long time

Nucleic acid amplification
* rapid and more sensitive than acid-fast smear

30
Q

How can latent TB be diagnosed? (2)

A

Two immune-based tests:

  1. Tuberculin skin test (PPD)
  2. Interferon gamma release assays (IGRAs)

However, we know that most people with positive tests will never develop an active disease (only 5-10% will)

31
Q

Briefly describe the key points of TB treatment (you won’t really be tested on this)

A
  • At least 2 antibiotics at all times to prevent MTB from developing resistance (initially, at least 3-4 drugs)
  • Prolonged therapy (usually at least 6 months long)
  • 3 important drugs:
  • Isoniazid (INH)
  • Rifampin (RIF)
  • Pyrazinamide (PZA)
32
Q

Active TB is a reportable disease, i.e….

A

Active TB must be reported to public health authorities at the time of diagnosis, by Quebec law.
Also, treatment for contagious forms of TB is mandatory, by Quebec law.

33
Q

How is latent TB treated?

A

Single drug therapy is adequate (relatively long treatment - 3-4 months)

34
Q

Do patients with latent TB require treatment?

A

Not everyone with latent TB requires treatment, and latent TB is not reportable.

35
Q

What are some adverse effects of TB treatment?

A

Liver toxicity (can be fatal, and risk increases with age).

Therefore, balance risk vs benefits esp. in individuals with latent TB.

36
Q

Describe key epidemiology features of TB in Canada (2)

A
  • Overall TB rates in Canada have decreased and “plateaud” in the last 20 years
  • Mortality declined rapidly after TB treatment became available
37
Q

What demographic of the Canadian population is disproportionally affected by TB?

A

Indigenous peoples, especially the Inuit

38
Q

Indigenous people account for … of all persons with TB in Canada.

A

17%

39
Q

Describe the key trends of TB in Indigenous Peoples in Canada

A
  • High incidence in Inuit populations (100/100,000)
  • 100 times higher incidence in Indigenous vs non-Indigenous
  • Substantial variation between communities
40
Q

Historically, in Canada, TB was a major cause of death in…

A

residential schools.

41
Q

The overall estimated global incidence rate of TB was 133 new cases per 100,000 - how does this compare to the Canadian rate?

A

That is over 25 times the Canadian rate!

42
Q

Before the Covid-19 pandemic, TB was…

A

the leading cause of death from a single infectious agent

43
Q

What were the impacts of Covid-19 on diagnosis and treatment of TB

A

Inadequate care, increased mortality, increased transmission

44
Q

What is an important challenge in TB treatment?

A

Antibiotic resistance

45
Q

“Non-tuberculous mycobacteria” refers to…

A

all mycobacteria EXCEPT MTB and Mycobacterium leprae.

46
Q

How many species of non-tuberculous mycobacteria? Do they cause human disease?

A

150 species - most do not cause human disease

47
Q

Why do non-tuberculous mycobacteria not automatically require treatment and are not reportable?

A

They do not directly spread between humans (they are not contagious) and may be present in humans without causing disease (colonizers/bystanders).

48
Q

What non-tuberculous mycobacterium is most often associated with human disease?

A

Mycobacterium avium

49
Q

Which is more common in Canada?
a) Mycobacterium tuberculosis
b) Mycobacterium avium

A

b) Mycobacterium avium

50
Q

What is the difference between active and latent TB tests?

A

Active: microbiologic tests
Latent: immunologic tests

51
Q

What are some major syndromes seen in pulmonary M. avium complex disease?

A
  • Nodular lung infiltrates associated with bronchiectasis on CXR
  • Cavitary lung disease
52
Q

M. avium disease is often seen in people with…

A

previously underlying lung disease (eg. CF, bronchiectasis, scarring)

53
Q

M. avium disease symptoms

A

cough, sputum, fatigue, weight loss

54
Q

Disseminated M. avium disease is seen in…

A

persons with advanced, uncontrolled AIDS or severely immunocompromised persons (eg. post-transplant).

Common symptom of disseminated M. avium is diarrhea

BLOCK B - RESPIRATION (31 decks)

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