W13 - mycobacterium diseases (TB) Flashcards
What percentage of the worlds population is infected with TB?
33.3%
Where can we find non-tuberculous mycobacteria (NTM)? Can you clean them off?
in (1) water, (2) soil, (3) contaminated surfaces
No b/c they form biofilms
What is the cutoff time of seeing visible colonies of mycobacterium for classification into slow-growing or rapid-growing?
slow-growing = more than 7 days
rapid-growing = less than 7 days
M. avium
M. tuberculosis
M. bovis
- is each rapid-growing or slow-growing?
All are slow-growing
Are micobacterium G+ or G-?
If they had to be classified as one or the other, they would be G+
Describe the shape and motility of mycobacterium
Describe 3 things special to their cell walls
non-motile rod-shaped bacteria
- Long-chain fatty acids (mycolic acid)
- Complex waxes
- Glycolipids
Describe 2 stains (1 IF and 1 acid fast) for mycobacterium
Auramine-rhodamine (IF)
Ziehl Neelson (acid fast stain)
Non-tuberculous mycobacterium (NTM):
- how do they spread?
- are they sensitive to classical anti-TB Rx?
- little risk of person-to-person transmission; usually by contact with contaminated surface/water/soil
- common resistant
slow-growing non-tuberculous mycobacterium (NTM):
- What does each cause:
1) M. avium complex
2) M. chimera
3) M. marinum
4) M. ulcerans
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)
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?
- 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)
Name (5) criteria/investigations for diagnosing NTM?
- Background of lung disease (pulmonary symptoms; nodular/cavitary opacities; multifocal bronchiectasis with multiple small nodules)
- Exclusion of other diagnoses
- Sputum culture => POSITIVE on >1 sample
OR
- POSITIVE BAL
OR
- POSITIVE biopsy with granulomata
Describe treatment of NTM?
I.e. for a MAC (mycobacterium avium complex):
- Clarithromycin/azithromycin (macrolide backgone)
- Rifampicin
- Ethambutol
+/- Amikacin/streptomycin
- if localised source, surgical intervention
Mycobacterium leprae - what are the 2 ends of the spectrum?
Paucibacillary tuberculoid (mild) => multibacillary lepromatous (disfiguring)
If you have a patient with TB you have to test them for
HIV
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!
10% provided they are HIV-
Mycobacterium tuberculosis - obligate _______ and generation time is ________ hours
aerobe
15-20h
How is mycobacterium tuberculosis transmitted?
What is its infectious dose?
How long is air infectious for?
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
What are 4 RFs for reactivation of latent TB?
- Immunosuppression
- Chronic alcohol excess
- Malnutrition
- Ageing
What is the typical clinical image of primary TB infection?
- 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
_____% of patients with latent TB will have reactivation
5-10%
What 2 forms of TB usually develop if the host is severely immuncompromised?
- Meningeal
- Miliary
The type of granulomas seen in TB are ______ ________
caseating granulomata
Where is TB most commonly found in the lungs? and why?
upper right lobe = it’s the best ventilated area and worst perfused area
Name 7 risk factors for catching TB
- Non-UK born/recent migrants (South Asia; Sub-Saharan Africa; Brazil)
- HIV
- Other immunocompromised
- Homeless
- Drug users, prison
- Close contacts
- Young adults (also higher incidence in elderly)
What are the symptoms (7) of active TB?
- Fever
- Weight loss
- Anorexia
- Night sweats
- Cough 80%
- Haemoptysis
- Malaise
What investigations (5) do you order if you suspect active TB?
- Sputum (x3 induced sputum) => stain for AAFBs (IF, Z stain)
- Sputum => culture, PCR NAAT
- Bronchoscopy + BAL => histology
- EMU = low yield test
- CXR
What investigations (2) do you do if you suspect latent TB?
- Tuberculin skin test (Mantoux test)
- IFN gamma release assays (IGRA)
Normal treatment for active TB
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)
