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Mycobacterial diseases Flashcards

(45 cards)

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1
Q

What are mycobacterium?

A

Non motile rod shaped bacteria which are slow growing

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2
Q

What do mycobacteria have in their cell wall?

A

Long chain fatty (mycolic) acids, complex waves and glycolipids in cell wall

THEREFORE they are acid alcohol fast

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3
Q

What stain do you use for TB/ AFB?

A

Ziehl Neelson - Red on blue

Auramine - Yellow

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4
Q

How do you get non TB mycobacteria?

A

Environmental
Water
Soil

Atypical

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5
Q

What is non TB mycobacterium from?

A

Ubiquitous in nature

Varying spectrum of pathogenicity

No person-to-person transmission

Commonly resistant to classical anti-TB Rx

May be found colonising

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6
Q

What are the slow growing NTM?

A

Mycobacterium avium intracellulare

M marinum

M ulcerans

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7
Q

What is MAI?

A 
Mycobacterium avium intracellulare (MAI)
AKA M. avium complex (MAC)
Immunocompetent
May invade bronchial tree
Pre-existing bronchiectasis or cavities
Immunosuppressed
Disseminated infection
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8
Q

What is rapid growing NTM?

A

M. abscessus, M. chelonae, M. fortuitum

Skin & soft tissue infections

In hospital settings, isolated from BCs
Vascular catheters & other devices

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9
Q

What is the epidemiology of MTB?

A

Getting better

Endemic to asia and africa

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10
Q

What are the RFs of MTB?

A

COPD
Asthma
Previous MTB
Lung cancer

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11
Q

How do you diagnose lung MTB?

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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12
Q

How do you treat MTB?

A

Rifampicin (6 months)
Isoniazid (6 months)
Pyrazinamide (2 months)
Ethambutol (2 months)

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13
Q

How do you treat MAI?

A

Clarithromycin/azithromycin
Rifampicin
Ethambutol
+/- Amikacin/streptomycin

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14
Q

How do you treat rapid growing NTM?

A

Based on susceptibility testing, usually macrolide-based

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15
Q

What is mycobacterium leprae?

A

Paucibacillary tuberculoid

Multibacillary Lepromatous

Mostly in S America, Africa and Asia

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16
Q

What is the in depth epidemiology of MTB?

A

Multisystem disease

Common worldwide
2nd most common cause of death by infectious agent (after HIV)
~2 million deaths each year

Increasing incidence since 1980s
Most common opportunistic infection in HIV
Immigration

9000 cases reported p.a. in UK

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17
Q

What kind of aerobe is MTB?

A

An obligate aerobe, generation time 15-20h

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18
Q

How is MTB transmitted?

A

Droplet/ 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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19
Q

How do you prevent MTB?

Study These Flashcards
A

Detection of cases- treat index case

Prevent transmission- PPE, negative pressure isolation

Optimisation of susceptible contacts- Address RFs, Vaccinations

20
Q

What are the MTB vaccines?

Study These Flashcards
A

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

21
Q

What is the natural history of TB?

Study These Flashcards
A 
Primary TB
Usually asymptomatic
Ghon focus/complex
Limited by CMI
Rare allergic reactions include EN
Occasionally disseminated/miliary

Latent TB

Reactivation

22
Q

What is post primary TB?

Study These Flashcards
A

Reactivation or exogenous re-infection

> 5 years after primary infection

5-10% risk per lifetime

Risk factors for reactivation
Immunosuppression
Chronic alcohol excess
Malnutrition
Ageing

Clinical presentation
Pulmonary or extra-pulmonary

23
Q

What is the most to least effective immune response to TB?

Study These Flashcards
A 
Healthy contact (LTBI)
Lymph node (Scrofula TB)
Localised Extrapulmonary

Pulmonary (localized)
Pulmonary (widespread)

Meningeal
Miliary

24
Q

What are the X-ray findings of MTB?

Study These Flashcards
A

Caseating granulomata
Lung parenchyma
Mediastinal LNs

Commonly upper lobe

25
What are some common extra pulmonary TB?
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
26
What is bone/joint and TB meningitis and miliary TB?
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
27
What is the clinical approach to MTB?
Index of suspicion Suggestive symptoms Detailed history Investigations Treatment Preventing onward transmission
28
What are RFs for TB?
Non-UK born/recent migrants South Asia 54.8% Sub-Saharan Africa 29.5% HIV Other immunocompromise Homeless Drug users, prison Close contacts Young adults (also higher incidence in elderly)
29
What is presentation of MTB?
``` FLAWS: Fever Lethargy/ Malaise 68% Appetite loss/ Anorexia Weight loss 74% Sweats (Night) 55% ``` Pulmonary symptoms: Cough 80% Haemoptysis 6-37%
30
What would you find on history and exam of MTB?
``` Other localising symptoms Pulmonary 54.1% Extra-pulmonary LN 20.4% GI 4.1% Spine 4.1% Meningitis 2% GU 1.3% ``` Ethnicity Recent arrival or travel Contacts with TB BCG vaccination Non-specific examination findings
31
What investigations do you do for TB?
CXR & other radiology ``` Sputum x3 Induced sputum Bronchoscopy Biopsies EMU ``` Stain for AAFBs (“smear”) Culture NAAT- Gene Xpert Histology Tuberculin skin test IGRAs- e.g. T Spot
32
What do you see on a sputum of TB?
Sputum 60% sensitivity Increased 10% & 2% with 2nd & 3rd sputa Gastric aspirates in kids Other specimens centrifuged Rapid Operator dependent
33
How do you do a TB culture?
Gold standard Solid & liquid culture systems Up to 6 weeks 1-3 weeks with modern automated systems Further testing of cultured isolates
34
What additional tests can you do for TB?
Speciation NAAT Chromatography Drug sensitivity Role of NAAT for primary samples? Rapid diagnosis of smear +ve Drug resistance mutations
35
How good is the tuberculin skin test?
Previous exposure to Mycobacteria 2 units tuberculin Delayed type hypersensitivity reaction Cross-reacts with BCG Poor sensitivity HIV, age, immunosuppressants Overwhelming TB
36
What is an IGRA?
Detection of antigen-specific IFN-γ production ELISpot Quantiferon No cross-reaction with BCG Cannot distinguish latent & active TB Similar problems with sensitivity & specificity
37
What are anti TB drugs?
RHZE (RIPE) + ``` Second line Quinolones (Moxifloxacin) Injectables Capreomycin, kanamycin, amikacin Ethionamide/Prothionamide Cycloserine PAS Linezolid Clofazamine ```
38
What are the side affects of 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
39
How long do you give TB treatment?
``` Duration 3 or 4 drugs for 2/12 Then Rifampicin & Isoniazid 4/12 10/12 if CNS TB Cure rate 90% ``` Adherence Directly observed therapy (DOT) Video observed therapy (VOT)
40
What is MDR TB?
Multi-drug resistant TB (MDR) Resistant to rifampicin & isoniazid Extremely drug-resistant TB (XDR) Also resistant to fluoroquinolones & at least 1 injectable Spontaneous mutation + inadequate treatment Likelihood increased Previous TB Rx HIV+ Known contact of MDR TB Failure to respond to conventional Rx >4 months smear +ve/>5 months culture +ve 4/5 drug regimen, longer duration Quinolones, aminoglycosides, PAS, cycloserine, ethionamide
41
What are the challenges in a TB history?
Clinical history Less likely to be classical Symptoms and signs often absent in population with low CD4 count (data from a number of cohorts starting HAART in Africa) Chest X-ray More likely extrapulmonary X-ray changes variable Smear microscopy & culture Less sensitive Tuberculin skin test More likely to be negative ``` Sensitivity of IGRAs for active tuberculosis (Goletti et al PloS One 2008) Quantiferon Gold 78.1% (95% CI 70.7, 84.3) T SPOT 85.1% (95% CI 79.2, 89.9) ```
42
How many people have TB?
33%
43
The laboratory calls you saying they have found Acid Fast Bacilli in a clinical sample. Which answer is most appropriate?
Recommend TB therapy
44
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?
10% HIV +ve, risk = 10% per year
45
Which drug is the most important?
Rifampicin is the most important drug

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