W13 - mycobacterium diseases (TB)

Question 1

What percentage of the worlds population is infected with TB?

Answer 1

33.3%

Question 2

Where can we find non-tuberculous mycobacteria (NTM)? Can you clean them off?

Answer 2

in (1) water, (2) soil, (3) contaminated surfaces

No b/c they form biofilms

Question 3

What is the cutoff time of seeing visible colonies of mycobacterium for classification into slow-growing or rapid-growing?

Answer 3

slow-growing = more than 7 days

rapid-growing = less than 7 days

Question 4

M. avium

M. tuberculosis

M. bovis

• is each rapid-growing or slow-growing?

Answer 4

All are slow-growing

Question 5

Are micobacterium G+ or G-?

Answer 5

If they had to be classified as one or the other, they would be G+

Question 6

Describe the shape and motility of mycobacterium

Describe 3 things special to their cell walls

Answer 6

non-motile rod-shaped bacteria

1. Long-chain fatty acids (mycolic acid)
2. Complex waxes
3. Glycolipids

Question 7

Describe 2 stains (1 IF and 1 acid fast) for mycobacterium

Answer 7

Auramine-rhodamine (IF)

Ziehl Neelson (acid fast stain)

Question 8

Non-tuberculous mycobacterium (NTM):

• how do they spread?
• are they sensitive to classical anti-TB Rx?

Answer 8

• little risk of person-to-person transmission; usually by contact with contaminated surface/water/soil
• common resistant

Question 9

slow-growing non-tuberculous mycobacterium (NTM):

• What does each cause:

1) M. avium complex

2) M. chimera

3) M. marinum

4) M. ulcerans

Answer 9

1) M. avium complex

• in immunocompetent => may invade bronchial tree, but have to have pre-existing bronchiectasis/cavities
• immunosuppressed

2) M. chimera = associated with cardiothoracic procedures

3) M. marinum = swimming pool granuloma (granulomas in skin/soft tissue)

4) M. ulcerans = skin lesions = chronic progressive painless ulcers (delibitating)

Question 10

M. abscessus, M. chelonae, M. fortuitum

• What type of NTM (non-tuberculous mycobacterium) are they?
• What type of infections do they cause?
• What are 2 risk factors?

Answer 10

• Rapid-growing NTM
• Skin & soft tissue infections from tattoo-associated outbreaks and jaccuzi
• In hospital sessions from BCs (vascular catheters, plastic surgery complications)
• CF and bronchiectasis (RFs)

Question 11

Name (5) criteria/investigations for diagnosing NTM?

Answer 11

1. Background of lung disease (pulmonary symptoms; nodular/cavitary opacities; multifocal bronchiectasis with multiple small nodules)
2. Exclusion of other diagnoses
3. Sputum culture => POSITIVE on >1 sample

OR

4. POSITIVE BAL

OR

5. POSITIVE biopsy with granulomata

Question 12

Describe treatment of NTM?

Answer 12

I.e. for a MAC (mycobacterium avium complex):

1. Clarithromycin/azithromycin (macrolide backgone)
2. Rifampicin
3. Ethambutol

+/- Amikacin/streptomycin

• if localised source, surgical intervention

Question 13

Mycobacterium leprae - what are the 2 ends of the spectrum?

Answer 13

Paucibacillary tuberculoid (mild) => multibacillary lepromatous (disfiguring)

Question 14

If you have a patient with TB you have to test them for

Answer 14

HIV

Question 15

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?

0.1%

1%

10%

Don’t worry, be happy!

Answer 15

10% provided they are HIV-

Question 16

Mycobacterium tuberculosis - obligate _______ and generation time is ________ hours

Answer 16

aerobe

15-20h

Question 17

How is mycobacterium tuberculosis transmitted?

What is its infectious dose?

How long is air infectious for?

Answer 17

droplet nuclei/airborne, <10 microM particles, remains suspended in air and has to reach lower airway macrophages

• infectious dose is 1-10 bacilli

air remains infectious for 30 mins => less if there is good ventilation

Question 18

What are 4 RFs for reactivation of latent TB?

Answer 18

1. Immunosuppression
2. Chronic alcohol excess
3. Malnutrition
4. Ageing

Question 19

What is the typical clinical image of primary TB infection?

Answer 19

• usually asymptomatic
• Imaging: Ghon focus(calcified granuloma; if there is an ipsilateral medistinal lymphadenopathy it’s called Ghon complex)
• sometimes erythema nodulosum
• ocassionally disseminated/miliary TB

most becomes latent TB

Question 20

_____% of patients with latent TB will have reactivation

Answer 20

5-10%

Question 21

What 2 forms of TB usually develop if the host is severely immuncompromised?

Answer 21

1. Meningeal
2. Miliary

Question 22

The type of granulomas seen in TB are ______ ________

Answer 22

caseating granulomata

Question 23

Where is TB most commonly found in the lungs? and why?

Answer 23

upper right lobe = it’s the best ventilated area and worst perfused area

Question 24

Name 7 risk factors for catching TB

Answer 24

1. Non-UK born/recent migrants (South Asia; Sub-Saharan Africa; Brazil)
2. HIV
3. Other immunocompromised
4. Homeless
5. Drug users, prison
6. Close contacts
7. Young adults (also higher incidence in elderly)

Question 25

What are the symptoms (7) of active TB?

Answer 25

1. Fever
2. Weight loss
3. Anorexia
4. Night sweats
5. Cough 80%
6. Haemoptysis
7. Malaise

Question 26

What investigations (5) do you order if you suspect active TB?

Answer 26

1. Sputum (x3 induced sputum) => stain for AAFBs (IF, Z stain)
2. Sputum => culture, PCR NAAT
3. Bronchoscopy + BAL => histology
4. EMU = low yield test
5. CXR

Question 27

What investigations (2) do you do if you suspect latent TB?

Answer 27

1. Tuberculin skin test (Mantoux test)
2. IFN gamma release assays (IGRA)

Question 28

Normal treatment for active TB

Answer 28

rifampicin, isoniazid (with pyridoxine), pyrazinamide, ethambutol for 2 months

then

rifampicin and isoniazid (with pyridoxine) for a further 4 months.

total 6 months

+ vitamin D

+ good nutrition (maintain weight)