Mycobacterial Diseases

Question 1

What is the microbiology of mycobacteria?

Answer 1

Non motile, rod shaped
Long chain fatty acids, complex waxes and glycolipids in cell wall - structural rigidity, compete freunds adjuvant potent necrotising factor, staining characteristics
Acid alcohol fast, hold onto zn stain and auramine which has higher sensitivity

Question 2

Where can NTM be identified?

Answer 2

Remote streams, shower head, whirl pool (pseudomonas), fish tank (marina)
Soil, ubiquitous
Varied pathogenicity
No person to person transmission
Resistant to classical anti TB drugs
Can colonise
Use clarithromycin and drugs used for mdr TB

Question 3

What are the slow growing NTM?

Answer 3

MAI- aka m avium complex, in immunocompetent may invade bronchial tree, pre existing bronchiectasis or cavities. In immunocompromised- disseminated infection
M marinum- swimming pool granuloma
M ulcerans- skin lesions eg bairnsdale ulcer, buruli ulcer, chronic progressive painless ulcer. Surgical debridement

Question 4

What are the rapidly growing NTM?

Answer 4

Abcessus, chelonae, fortuitum
Skin and soft tissue infections
In hospital settings
Respond to erythromycin and doxyclyin

Question 5

What are the risk factors for NTM?

Answer 5

60/70’s, airways disease, previous TB eg cavities, asthma, bronchiectasis, complement deficient, cf, cancer

Question 6

What is the diagnosis for NTM?

Answer 6

Lung disease- pulmonary symptoms, opacities, multifocal bronchiectasis
Exclusion of other diagnoses
Positive culture of more than one sample
Positive BAL
Positive biopsy with granulomata

Question 7

What is treatment for NTM?

Answer 7

Susceptibility testing may not reflect clinical usefulness
MAI- clari, azithryomycin
Rifampcin
Ethambutol
+/- amikacin, streptomycin
Rapid growing NTM- macrolide based 18-24 months

Question 8

What is m leprae?

Answer 8

Paucibacillary tuberculoid- cell response is huge, peripheral neuropathy
load of bacteria and cell mediated immunity
Multibacillary lepromatous- lumps and bumps
Lateral eyebrow loss, thickened nerve?
Still common

Question 9

What is mtb?

Answer 9

Multi system disease
2nd most common cause of death by infectious agent after HIV
Most common opportunistic infection in HIV
7 closely related species, tb, bovis resistant to pyrizinamide, africanum
Obligate anaerobes, generation time 15-20 hours

Question 10

What are the TB disease States?

Answer 10

Exposed individual 
Active TB quickly (2years) HIV 
Uninfected 
Cleared infection, natural immunity 
Contained- majority of 3rd of people who have TB, lifetime risk of activation.
Mantoux test- induration not erythema

Question 11

How is TB transmitted?

Answer 11

Droplet nuclei/airborne 
Less than 10microm particles 
Suspended in air 
Reach lower airway macrophages 
Infectious dose 1-10 bacilli 
3000 infectious nuclei- cough, talking 5 mins 
Air remains infectious for 30 mins

Question 12

How can TB be prevented?

Answer 12

Detection of cases
Treatment of index case
Prevention of transmission- Personal Protective Equipment, negative pressure isolation
Optimisation of susceptible contacts- vaccination 70-80% effectiveness in preventing severe childhood TB, protection wanes
Inflixumab- TB cases TNF link/immunocompromised link

Question 13

What is the natural history of TB?

Answer 13

Primary- asymptomatic, ghon focus complex
Limited by CMI
Rare allergic reactions include erythema nodosum
Occasionally disseminated
Latent
Reactivation

Question 14

Why would you get post primary TB?

Answer 14

Failure of cell mediated immunity, immune system wanes 30 years old
Immunosuppression, chronic alcohol excess, malnutrition, ageing
Pulmonary or extra pulmonary

Question 15

How can the host response shape clinical outcome?

Answer 15

Less effective immune response >>
Healthy context- ltbi
Lymphadenitis
Localised extrapulmonary
Pulmonary localised/widespread- caseating granulomata, upper lobe
Meningeal
Miliary

Question 16

What is the presentation of extra pulmonary TB?

Answer 16

Lymphadenitis- scrofula, cervical lymph nodes,abscess and sinus
GI- swallowing of tubercles (lavage in kids)
Peritoneal- ascitic or adhesive looks like crohns
Genitourinary- slow progression to renal disease, subsequent spreading to lower urinary tract sterile pyuria
Bone and joint- haematogenous spread, spinal TB venous plexus nearby, potts
Military- seeds on cxray, progressive disseminated haematogenous TB, increasing due to HIV
Meningitis- Africa and Vietnam

Question 17

What is the clinical approach to TB?

Answer 17

High index of suscpicion
Suggestive symptoms 
Ix culture and histology 
Tx
Preventing onward transmission

Question 18

What should be included in hx and examination?

Answer 18

Ethnicity, travel, contacts with TB, bcg vaccination, non specific examination findings

Question 19

What investigations are needed for TB?

Answer 19

Cxr mediastinal, para tracheal stripe widened
Sputum times 3
Bronchoscopy, biopsies, emu
Stains
Culture
NAAT- PCR point of care
Histology
Tuberculin skin test- mycobacteria, relies on lots of things, delayed hypersensitivity, cross reacts with bcg
Igra- detection of antigen specific ifn gamma production, enzyme linked immune asay. Cannot distinguish latent and active

Question 20

What is the smear in TB involving?

Answer 20

60% sensitivity
Gastric aspirates in kids
Other specimens centrifuged urine and csf
Rapid, operator dependant

Question 21

What is the treatment for TB?

Answer 21

Rifampcin- raised transaminases and induces cytochrome p450 , orange secretions
Isoniazid- peripheral neuropathy, hepatotoxicity
Pyrazinamide- hepatotoxicity
Ethambutol- visual disturbance
RI for 4 months Dot/vot
Vit d
Surgery

Question 22

What is mutli drug resistant TB?

Answer 22

Resist to r and I
Extremely drug resistant- fluoroquinolones and at least one injectable
Spontaneous mutation and inadequate treatment
Previous TB, HIV, known contact to mdr TB, 4 months positive smear, 5 months positive culture
4/5 drug regimen

Question 23

What are the challenges in TB and HIV diagnosis?

Answer 23

Clincal history- less likely to be classical, symptoms absent in low cd4 count
Chest X-ray- more likely extrapulmonary, x Ray changes variable
Smear microscopy and culture- less sensitive
Skin test- more likely to be negative
Timing of tx
Drug interaction
Overlapping toxicity
Adherence

Question 24

What categories can mycobacteria be divided into?

Answer 24

Slow growing6-8 weeks, TB MTB complex is bovia and tuberculosis. MAC- avium and intracellulare immunocompromised hosts
Rapidly growing 3-5 days- abscesssus complex, abcessus, massilense, bolletti, immunocompromised
Ungrouped- leprae