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Year 5 - Pathology > MICRO: Mycobacterial diseases (TB) > Flashcards

MICRO: Mycobacterial diseases (TB) Flashcards

1
Q

What % of world’s population is infected with TB?

A

33%

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2
Q

What is the difference between NTM and MTB?

A

NTM - non-tuberculous mycobacteria (usually environmental)

MTB - mycobacterium tuberculosis

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3
Q

What is “slow growing” mycobacteria?

A

<7 days = rapid-growing e.g. M abscessus complex (affect CF patients)

>7 days = slow growing e.g. MTB complex (e.g. MTB and M bovis BCG) and M.avium complex (M avium and M intracellulare)

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4
Q

What are the microbiological features of mycobacteria?

A
  • Non-motile rod-shaped bacteria
  • Relatively slow-growing compared to other bacteria
  • Long-chain fatty (mycolic) acids, complex waxes & glycolipids in cell wall
    • Structural rigidity
    • Staining characteristics
  • Acid alcohol fast
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5
Q

How common is transmission in NTM?

A

Uncommon but may colonise humans

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6
Q

What are the features of myobacterium avium complex?

A

Slow growing

Immunocompetent

  • May invade bronchial tree
  • Pre-existing bronchiectasis or cavities

Immunosuppressed

  • Disseminated infection
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7
Q

Who is affected by mycobacterium chimera, marinum and ulcerans?

A

(NB: also all slow growing)

Mycobacterium chimera

  • Associated to cardiothoracic procedures

M. marinum

  • Swimming pool granuloma

M. ulcerans

  • Skin lesions e.g. Bairnsdale ulcer, Buruli ulcer
  • Chronic progressive painless ulcer
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8
Q

What are the rapid growing NTMs?

A
  1. M. abscessus,
  2. M. chelonae,
  3. M. fortuitum
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9
Q

What type of infections are caused by rapid growing NTMs?

A
  • Skin & soft tissue infections
    • Tattoo associated outbreaks
  • In hospital settings, isolated from BCs
    • Vascular catheters & other devices
    • Plastic surgery complications
  • CF and bronchiectasis
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10
Q

Which are the slow growing NTMs?

A
  1. Mycobacterium avium complex
  2. Mycobacterium chimera
  3. M. marinum
  4. M. ulcerans
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11
Q

How do you diagnose NTM infections?

A

BTS 2017 guidelines/ IDSA guidelines 2020

Lung disease

  • Clinical: pulmonary symptoms, nodular/cavitary opacities, multifocal bronchiectasis with multiple small nodules
  • Exclusion of other diagnoses

Microbiologic:

  • Positive culture >1 sputum samples
  • OR +ve BAL
  • OR +ve biopsy with granulomata

(make sure to send MC&S)

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12
Q

What is the treatment of NTM infections?

A

Susceptibility testing results may not reflect clinical usefulness

MAC

  • Clarithromycin/azithromycin
  • Rifampicin
  • Ethambutol
  • +/- Amikacin/streptomycin

Rapid-growing NTM

  • Based on susceptibility testing, usually macrolide-based
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13
Q

What is leprosy caused by? How does it present (2)?

A

Mycobacterium leprae

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14
Q

What are the risk factors for NTM?

A
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15
Q

How has COVID affected TB?

A

TB was the biggest killer perviously then COVID took over in 2020

Fewest cases diagnosed in for years when COVID became prevalent

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16
Q

How is TB transmitted?

A
  • Droplet nuclei/airborne
    • <10µm particles
    • Suspended in air
    • Reach lower airway macrophages
  • Infectious dose 1-10 bacilli
  • 3000 infectious nuclei
    • Cough
    • Talking 5 mins
  • Air remains infectious 30 mins
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17
Q

How effective is BCG and what is it not effective againts?

A

70-80% but protection wanes

Only given to high prevalence communities

Protects against CNS tuberculousis but not pulmonary TB

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18
Q

What are the 3 forms of TB infections?

A

Primary TB

  • Usually asymptomatic
  • Ghon focus/complex
  • Limited by CMI
  • Rare allergic reactions include EN
  • Occasionally disseminated/miliary

Latent TB

Reactivation

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19
Q

What are the risk factors for post-primary TB/reactivation?

A

5-10% lifetime risk

Risk factors for reactivation

  • Immunosuppression
  • Chronic alcohol excess
  • Malnutrition
  • Ageing
20
Q

List how a less effective immune response leads to more severe forms of TB.

A
21
Q

What is seen in pulmonary TB? Where is it usually found?

A
  • Commonly in upper lobe
  • Caseating granulomata of lung parenchyma and mediastinal LN
22
Q

What is lymphadenitis TB (extra-pulmonary) also known as?

A

Scrofula and cervical lymph nodes are most commonly affected

23
Q

What are the risk factors/demographics for TB?

A
  • Non-UK born/recent migrants
  • South Asia
  • Sub-Saharan Africa
  • HIV
  • Other immunocompromise
  • Homeless
  • Drug users, prison
  • Close contacts
  • Young adults (also higher incidence in elderly)
24
Q

What are the signs/symptoms of TB?

A
  • Fever
  • Weight loss 74%
  • Night sweats 55%
  • Pulmonary symptoms
    • Cough 80%
    • Haemoptysis 6-37%
  • Malaise 68%
  • Anorexia

But depends on site affected

25
Q

List some sites that can be affected by TB (extrapulmonary).

A

Lymphadenitis

  • AKA scrofula
  • Cervical LNs most commonly

Abscesses & sinuses

Gastrointestinal - swallowing of tubercles

Peritoneal - Ascitic or adhesive

Genitourinary

  • Slow progression to renal disease
  • Subsequent spreading to lower urinary tract

Bone & joint

  • Haematogenous spread
  • Spinal TB most common
  • Pott’s disease

Miliary TB

  • Millet seeds on CXR
  • Progressive disseminated haematogenous TB
  • Increasing due to HIV

Tuberculous meningitis

26
Q

How many sputum samples are needed to diagnose TB?

A

x3

27
Q

What is a “smear” for TB testing for?

A

Acid fast bacilli

28
Q

What is this?

A

Granuloma

29
Q

What is the use of NAAT in TB diagnosis?

A

nucleic acid amplification test = NAAT

  1. rapid diagnosis of smear +ve TB
  2. drug resistance mutations detected
  3. along with chromatography, it is used for speciation
30
Q

What is the sensitivity of sputum for TB diagnosis?

A

60% sensitivity which increases by 10% with 2nd and 3rd samples of sputum

31
Q

What is the turnaround time for culture of TB?

A

6 weeks

32
Q

What is the treatment for TB including supportive?

A

Multi-drug therapy (RHZE)

Rifampicin (R)

  • Raised transaminases & induces cytochrome P450
  • Orange secretions

Isoniazid (H)

  • Peripheral neuropathy (pyridoxine 10mg od)
  • Hepatotoxicity

Pyrazinamide (Z)

  • Hepatotoxicity

Ethambutol (E)

  • Visual disturbance

Vitamin D

Nutrition

Surgery

33
Q

What is the duration of treatment for TB?

A

Duration

  • 3 or 4 drugs for 2/12
  • Then Rifampicin & Isoniazid 4/12
  • 12/12 if CNS TB
  • Cure rate 90%
34
Q

How do you ensure adherence to TB therapy?

A

DOT - directly observed therapy

VOT - video observed therapy

35
Q

How has prevalence of MDR TB changed?

A

Increasing and most common in Russia

36
Q

What is MDR TB resistant to?

A

Rifampicin and isoniazid

37
Q

What is extremely drug resistant TB resistant to? (XDR)

A

Resistant to fluoroquinolones and at least 1 injectible

38
Q

What are the risk factors for MDR TB?

A
  • Spontaneous mutation
  • Inadequate treatment
  • Previous TB Rx
  • HIV+
  • Known contact of MDR TB
  • Failure to respond to conventional Rx
  • >4 months smear +ve/>5 months culture +ve
39
Q

What is the treatment of latent TB?

A

rifampicin and isoniazid for 3 months - effective for penetrating the granuloma

40
Q

What is the treatment for MDR TB?

A

4 or 5 drug regimen, with a longer duration

  1. Quinolones,
  2. aminoglycosides,
  3. PAS,
  4. cycloserine,
  5. ethionamide,
41
Q

How does HIV affect the tuberculin skin test?

A

More likely to be negative

42
Q

How sensitive are IGRAs for active tuberculosis diagnosis?

A

70-90%

T-SPOT better than Quantiferon Gold

43
Q

What are the main challenges in TB and HIV treatement?

A
  • Timing of treatment initiation
  • Drug interactions
  • Overlapping toxicity
  • Duration of treatment – adherence
  • Health care resources
44
Q

What is a problem ith IGRAs? What do they detect?

A
  • Detect antigen specific IFN-gamma production
  • They cannot distinguish between latent and active TB
  • Problems with sensitivity and specificity
45
Q

How does the tuberculin skin test work? What are the main problems with it?

A
  • Detects previous exposure to mycobacteria
  • 2 units of tuberculin injected
  • Detection of delayed type hhypersensitivity reaction

BUT

  • cross-reacts with BCG
  • poor sensitivity - HIV, age, immunosuppressants, overwhelming TB.
46
Q

A 23 year old male is a close contact of a person with smear positive pulmonary TB, What is his lifetime risk of developing active TB?

  • 1.0.1%
  • 2.1%
  • 3.10%
  • 4.Don’t worry, be happy!
A

10%

Year 5 - Pathology (89 decks)

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