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Microbiology - Path > Mycobacterial disease > Flashcards

Mycobacterial disease Flashcards

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1
Q

Describe where non-tuberculous mycobacteria can be found, and how it spreads

A
  • Non-tuberculous mycobacteria is environmental and atypical - found in lakes/water and soil
  • Ubiquitous in nature
  • Varying spectrum of pathogenicity
  • No person-to-person transmission
  • Commonly resistant to classical anti-TB prescriptions
  • May be founf colonizing
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2
Q
  1. Who is at risk of developing slow-growing Non-tuberculous mycobacteria?
  2. What are the different types of slow growing NTM and where are they found?
A
  1. Immunocompetent and immunocompromised (at risk of disseminated infection)

2.

  • Mycobacterium avium intracellulare/ M.avium complex
  • M.marinum - swimming pool granuloma
  • M.ulcerans - Skin lesions e.g. Bairnsdale ulcer, Buruli ulcer - causing a chronic progressive painless ulcer
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3
Q
  1. What are the different ‘rapid-growing’ NTM?
  2. What do they cause?
A

1.

  • M.abscessus
  • M.chelonae
  • M.fortuitum

2.

  • Skin and soft tissue infections
  • In hospital settings, isolated BCs - vascular catheters and other devices
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4
Q

Describe the diagnosis of Non-tuberculous mycobacteria from the 2007 American thoracic society guidelines

A
  • 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
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5
Q

What is the treatment of Non-tuberculous mycobacteria?

A
  • Susceptibility testing results may not reflect clinical usefulness
  • MAI:
    • Clarithryomycin/azithromycin
    • Rifampicin
    • Ethamnutol
    • +/- Amikacin/streptomycin
  • Rapid-growing NTM
    • Based on susceptibility testing, usually macrolide-based
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6
Q

What are the two types of mycobacterium leprae?

A
  • Paucibacillary tuberculoid
  • Multibacillary lepromatous
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7
Q

Describe the epidemiology of mycobacterium tuberculosis

A
  • Multi-system disease
  • Common worldwide
    • 2nd most common cause of death by infectious agent
    • 2 million deaths each year
  • Increasing prevalence since 1980s
    • Most common opportunistic infection in HIV
    • Immigration
  • 9000 cases reported per annum in UK
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8
Q

What is the transmission of TB?

A
  • Droplet nuclei/airborne
    • <10um particles
    • Suspended in air
    • Reach lower airway macrophages
  • Infectious dose 1-10 bacilli
  • 3000 infectious nuclei
    • cough
    • talking for 5 minutes
  • Air remains infectious for 30 minutes
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9
Q

How can TB be prevented?

A
  • Detection of cases
  • Treatment of TB in a timely manner
  • Prevention of transmission
    • PPE
    • Negative pressure isolation
  • Optimisation of susceptible contacts
    • Address risk factors
    • Vaccination
      • Bacille Calmette-Guerin (BCG): Live attenuated M.bovis strain
      • Given to babies in high prevalence communities (only since 2005)
      • 70-80% effectiveness in preventing severe childhood TB
      • Protection wanes
      • Little evidence in adults
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10
Q

What is the natural history of pulmonaryTB?

A
  • Primary TB
    • Usually asymptomatic
    • Ghon focus/complex
    • Limited by CMI
    • Rare allergic reactions include EN
    • Occassionally disseminated/miliary
  • Latent TB
  • Reactivation
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11
Q
  1. Describe post-primary TB
  2. What are the risk factors for reactivation of TB?
A
  1. Post-primary TB:
  • reactivation or exogenous re-infection
  • > 5 years after primary infection
  • 5-10% risk per lifetime
  1. Risk factors for reactivation
  • Immunosuppression
  • Chronic alcohol excess
  • Malnutrition
  • Ageing

Clinical presentation - pulmonary or extra-pulmonary

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12
Q
A
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13
Q

Describe the radilogical features of pulmonary TB

A
  • Caseating granulomata
    • Lung parenchyma
    • Mediastinal Lymph nodes
  • Commonly upper lobe
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14
Q

Describe what can develop in people with Extra-pulmonary TB

A
  • Lymphadenitis
    • AKA scrofula
    • Cervical lymph nodes most commonly
    • Abscesses and sinuses
  • Gastrointestinal
    • Swallowing of tubercules
  • Peritoneal
    • Ascitic or adhesive
  • Genitiurinary
    • Slow progression to renal disease
    • Subsequent spreading to lower urinary tract
  • Bone and 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
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15
Q

What does this image show?

A

Millet seeds, a signs of Miliary TB

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16
Q

What is spinal TB known as?

A

Pott’s disease

17
Q

Describe the demographics and risk factors for TB

A
  • Non-UK born/recent migrants
    • south asia 54.8%
    • sub-saharan africa 29.5%
  • HIV or other immunocompromise
  • Homeless
  • Drug users, prison
  • Close contacts
  • Young adults
18
Q

What is the presentation of TB?

A
  • Fever
  • Weight loss 74%
  • Night sweats 55%
  • Pulmonary symptoms
    • cough 80%
    • haemoptysis 6-37%
  • Malaise 68%
  • Anorexia
19
Q

What are important questions to ask for someone who you suspect has TB?

A
  • Ethnicity
  • Recent arrival or travel
  • Contacts with TB
  • BCG vaccination
  • Non-specific examination findings
20
Q

What investigations should be performed in suscpected TB?

A
  • CXR and other radiology
  • Spuum x3 - induced sputum
  • Bronchoscopy
  • Biopsies
  • EMU

stain for AAFBs ‘smear’

culture

NAAT

Histology

Tuberculin skin test

IGRAs

21
Q

What does the image show?

A

Mediastinal lymph node

22
Q

Describe a smear for TB

A
  • Uses sputum
    • 60% sensitivity
    • Increases with more samples
  • Gastric aspirates in kids
  • Other specimens centrifuged
  • Rapid
  • Operator dependent
23
Q

Summarise different bacteriological examinations for TB

A
24
Q

Describe the use of cultures for diagnosing TB

A
  • Culture is gold standard
  • Solid and liquid culture systems
  • Takes up to 6 weeks - less with modern automated systems
25
Q

What do tuberculin skin tests show?

A
  • Tuberculin skin test shows previous exposure to mycobacteria
  • 2 units tuberculin
  • Delayed type hypersensitivity reaction (type 4)
  • Cross-reacts with BCG
  • Poor sensitivity
    • HIV, age, immunosuppressants
    • Overwhelming TB
26
Q

Describe the use of interferon gamma release assays (IGRAs)

A
  • Detection of antigen-specific IFN-gamma production
  • ELISpot
  • Quantiferon
  • No cross reaction with BCG
  • Cannot distinguish latent and active TB
  • Similar issues with sensitivity and specificity
27
Q

What are the first line medications for TB?

A
  • Rifampicin
  • Isoniazid
  • Pyrazinamide
  • Ethambutol

RIPE

28
Q

What are the second line medications for TB?

A
  • Quinolones (moxifloxacin)
  • Injectables - capreomycin, kanamycin, amikacin
  • Ethionamide/prothioamide
  • Cycloserine
  • PAS
  • Linezolid
  • Clofazamine
29
Q

The treatment for TB is RIPE, a multi-drug therapy. Describe the side effects of each of the antibiotics

A
  • Rifampicin
    • Raised transaminases and induces cytochrome P450
    • Orange secretions
  • Isoniazid
    • Peripheral neuropathy
    • Hepatotoxicity
  • Pyrazinamide
    • Hepatotoxicity
  • Ethambutol
    • Visual disturbance
30
Q

Describe the duration of treatment for TB

A
  • 3 or 4 drugs of RIPE for 2/12
  • Then Rifampicin and Isonazid 4/12
  • 10/12 if CNS TB
  • Cure rate 90%
31
Q

Describe Multidrug resistance TB

  • What is it against?
  • What has caused it?
A
  • Multidrug resistance TB - resistant to rifampicin and isonazid
  • Extremely drug resistant TB
    • Also resistant to fluoroquinolones and at least 1 injectable
  • Spontaneous mutation + inadequate treatment
  • Liklihood increased
    • Previous TB prescription
    • HIV positive
    • Known contact of multi-drug resistant TB
    • Failure to respond to conventional Rx
    • > 4 months smear +>5 months culture +ve
  • 4/5 drug regimen, longer duration
    • Quinolones, aminoglycosides, PAS, cycloserine and ethionamide
32
Q

Describe the following challenges with having TB and HIV when it comes to diagnosis of TB:

  1. Clinical history
  2. Chest X ray
  3. Smear microscopy and culture
  4. Tuberculin skin test
  5. Sensitivity of interferon gamma release assays for active tuberculosis
A
  1. Clinical history
  • Less likely to be classical
  • Symptoms and signs are often absent in population with low CD4 count
  1. Chest X-ray
  • More likely extrapulmonary
  • X-ray changes variable
  1. Smear microscopy and culture
    * Less sensitive
  2. Tuberculin skin test
    * More likely to be negative
  3. Sensitivity of IGRAs for active TB
  • Quantiferon - reduced
  • T SPOT - reduced
33
Q

What are the challenges in TB and HIV when it comes to treatment?

A
  • Timing of treatment initiation
  • Drug interactions
  • Overlapping toxicity
  • Duration of treatment - adherence
  • Health care resources
34
Q

Name two novel diagnostic tests

A
  • IGRAs - interferon gamma release assays
  • NAATs - Nucleic acid amplification tests

Microbiology - Path (12 decks)

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