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Microbiology > TB > Flashcards

TB Flashcards

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Biology 101 flashcards
1
Q

Is Mycobacterium tuberculosis aerobic or anaerobic?

A

Aerobic

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2
Q

Describe the features of Mycobacterium tuberculosis

A
  • ?Gram positive (according to path guide, but can appear both due to unusual cell wall. Ziehl-Neelson staining used instead of Gram stain)
  • Aerobic
  • Acid alcohol fast
  • Thick, waxy cell wall (complex, immunogenic)
  • Intracellular rod
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3
Q

Describe the common presentation of TB

A
  • Cough +/- haemoptysis
  • Fever
  • Night sweats
  • Weight loss (?anorexia)
  • Malaise
  • Ethnicity also important factor
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4
Q

What is post-primary TB?

A

Re-activation/re-infection of latent TB following an earlier primary infection (usually in childhood).

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5
Q

List 4 clinical features of a post-primary TB infection

A
  • Upper lobes affected
  • May progress rapidly to cavitation
  • Classic lesion: caseating granuloma
  • Healing leads to fibrosis and calcification
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6
Q

What is miliary spread of TB?

A
  • Progressive, disseminated haematogenous spread from the primary focus throughout the body.
  • Occurs in ~10% of primary TB when infection is not controlled.
  • Rare in post-primary.
  • ‘Rich foci’
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7
Q

Is miliary spread more common in primary or post-primary TB?

A

Primary

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8
Q

What are the common clinical features of primary TB infection?

A
  • Multiplies at pleural surface (Ghon focus)
  • Taken by macrophages to lymph node (primary complex)
  • Generalised lympho-haematogenous spread
  • Characteristic lesion = granuloma (Langhan’s giant cells)
  • Can be asymptomatic (esp in children)
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9
Q

What are the less common features of primary TB infection?

A
  • Tuberculoma
  • Miliary TB
  • ‘Progressive primary’ - focus/node ulcerates into bronchus, leading to pneumonia / cavity formation / bronchiectasis / consolidation / collapse
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10
Q

What are the first line treatments for TB?

A

RIPE

  • Rifampicin for 6 months
  • Isoniazid for 6 months
  • Pyrazinamide for 2 months
  • Ethambutol for 2 months
  • Adherence is key: observation of drug taking sometimes necessary for first 2 months (DOTS - directly observed treatment, short course)
  • Vitamin D supplements
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11
Q

In which cases does standard first line treatment vary?

A
  • TB meningitis and spinal TB: Rifampicin and isoniazid taken for 10-12 months. (Pyrazinamide and ethambutol as normal). Plus steroids in meningitis.
  • Latent TB/prophylaxis: 6 months isoniazid only
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12
Q

What are the side effects of Rifampicin?

A
  • Drug interactions (raised transaminases - CP450 induction)
  • Orange secretions
  • Hepatotoxicity
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13
Q

Bonus question: where does the word ‘miliary’ come from?

Hint: it’s not to do with hats

A

On CXR, the widely disseminated appearance of miliary TB lesions in the lungs looks like sprinkled milet seeds.

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14
Q

What are the side effects of isoniazid?

A
  • Peripheral neuropathy (give B6/pyrodoxine)

- Hepatotoxicity

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15
Q

What are the side effects of Pyrazinamide?

A
  • Hyperuricaemia

- Hepatotoxicity

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16
Q

What are the side effects of ethambutol?

A
  • Optic neuritis

- Visual disturbances

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17
Q

What are the second line treatments for TB?

A
  • Injectables (capreomycin, kanamycin, amikacin)
  • Quinolones (moxifloxacin)
  • Cycloserine
  • Ethionamide/Protionamide
  • PAS (P-aminosalicylic acid)
  • Linezolid
  • Clofazamine
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18
Q

What are the drug resistant strains of TB?

A
  • Mono - resistant to one drug only
  • MDRTB - resistant to Rifampicin and isoniazid
  • XDRTB - resistant to Rifampicin, isoniazid, Injectables (kanamycin/amikacin) and Quinolones
19
Q

Which investigations are necessary for TB?

A
  • Imaging: CXR (upper lobe cavitation - post primary) and CT
  • Cultures: sputum x3, bronchoalveloar lavage (BAL), urine (EMU), pus in “Lowenstein-Jensen medium” (gold standard)
  • Tuberculin skin tests (TSTs): Mantoux/Heaf using PPD
    Heaf = 6 skin pricks, discontinued in 2005
    Mantoux = manual, more accurate
  • Interferon Gamma Release assays (IGRAs): eg Elispot, Quantiferon - bloods taken, alternative to TST
  • Nucleic acid amplification tests (NAATs): PCR line probe assays, tests for sensitivities
  • Other: liquid culture mediums
20
Q

What imaging is needed to diagnose TB?

A

CXR (upper lobe cavitation seen in post-primary) and CT

21
Q

What cultures should be taken to diagnose TB?

A
  • Sputum x3
  • Bronchoalveloar lavage (BAL)
  • Urine (EMU)
  • Pus (in Lowenstein-Jensen medium)
22
Q

What is the “gold standard” test for TB?

A

Culture in Lowenstein-Jensen medium

23
Q

Which staining techniques can be used for TB microscopy?

A
  • Ziehl-Neelsen (aka acid fast)

- Auramine-rhodamine

24
Q

What is seen in TB microscopy?

A

Gram positive, acid fast, aerobic, intracellular rods

25
Q

What are the two tuberculin skin tests (TSTs) and what is the difference between them?

A
  • Mantoux and Heaf tests
  • Both involve introducing a purified protein derivative (PPD) of TB intradermally and assessing the reaction (size of induration) to determine any previous TB exposure.
  • Heaf test (6 pricks) used a special automated device which was discontinued in 2005.
  • The Mantoux test is an older, manual version which is now preferred and thought to be more accurate.
26
Q

What is an IGRA?

A

Interferon-gamma release assay.

Eg Elispot or Quantiferon. The standard blood test for TB and an alternative to the TST (Mantoux).

27
Q

What is a NAAT?

A

Nucleic acid amplification test.

A PCR-line probe assay, used to determine TB sensitivities (ie whether it is a resistant strain)

28
Q

What percentage of TB cases are extrapulmonary?

A

20%

29
Q

What are the sites/types of extrapulmonary TB?

A 
Meningitis 
Spinal 
Lymphadenitis
Pericarditis
Abdominal (peritonitis, ileitis)
Genito-urinary
Renal
Testicular
Skin
Liver
30
Q

What percentage of all TB cases are TB meningitis?

A

2%

31
Q

Describe the features of TB meningitis presentation

A 
Subacute
Weight loss
Fever
Night sweats
Headache 
Neck stiffness
Reduced GCS
Focal neurological deficit
32
Q

How is TB meningitis diagnosed?

A

Tuberculomata on CT and lymphocytic LP

33
Q

What is the treatment for TB meningitis?

A

12 months of RIPE and steroids

34
Q

What percentage of all TB cases are spinal TB?

A

4%

35
Q

What are the characteristic presenting features of spinal TB?

A

Fever
Sweats
Weight loss
Back pain

36
Q

What are the main steps in the pathogenesis of spinal TB?

A

1) Haematogenous spread
2) Initial discitis
3) Vertebral destruction and collapse +/- anterior extension (causing iliopsoas abscess)

37
Q

Describe the epidemiology and risk factors for TB in the UK

A

Increasing incidence, currently around 15/100,000 UK wide but as high as 150/100,000 in some London boroughs.

More common in young and elderly.

RFs: recent migrant, HIV+, homeless, prisoners, close contacts with TB.

38
Q

What are the risk factors for reactivation of latent TB?

A

Immunosuppression
Malnutrition
Ageing
Chronic alcohol excess

39
Q

What does the BCG stand for and what does the vaccination contain?

A

Bacille Calmette-Guerin

Contains an attenuated strain of Mycobacterium Bovis.

40
Q

What is the efficacy of the BCG vaccine?

A

Very variable: 0-80%

Good at protecting against TB meningitis, disseminated TB and leprosy but bad for pulmonary TB.

41
Q

Who should receive the BCG vaccination?

A

Babies born in or with parents/grandparents from areas with incidence >40/100,000

Previously unvaccinated new immigrants from high prevalence countries.

42
Q

In which group is the BCG vaccination contraindicated?

A

HIV patients

43
Q

What is the chance of latent TB becoming reactived in an HIV +ve patient?

A

5-10% Yearly risk (contrast with 5-10% lifetime risk if HIV -ve)

Microbiology (27 decks)

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