Mycobacterium Flashcards
What are non-tuberculous mycobacterium?
These are mycobacterium which are widely present in the environment and have no person-to-person transmission. Infection with them is associated with impaired immunity and these types have poor response to normal TB regimens.
What is the epidemiology surrounding tuberculosis?
- A third of all people are infected with TB
- The rates of new Tb cases is falling, but rates of NTMs are increasing
- It is the second most common cause of death by an infectious agent
What is the microbiology of mycobacterium?
- Slow-growing
- Has a long chain fatty-acid wall which gives it rigidity and its staining characteristics
What stains can be used?
Stains which show they are resistant to acid:
Rhodamine/auramine:
- Quicker
- Less operator dependant
Ziehl Neelsen
How is TB transmitted?
- Airborne and suspended in air
- 1-10 bacilli is an infectious dose
- In 5 minutes, 3000 can be expelled
- Air is infectious for 30 minutes
How can TB transmission be prevented?
- Detect and treat all cases
- Reduce transmission by PPE, negative pressure rooms and vaccination
How can TB be vaccinated against?
An attenuated strain of mycobacterium bovis is used (Bacille Calmette-Guerin - BCG). All children from high risk parents will receive and unvaccinated immigrants.
Use:
- Efficacy 0-80: bad for pulmonary TB, better for leprosy, meningitis, disseminated TB
- Good for preventing latent to active disease
Contraindications:
- HIV
Name and describe some NTMs
Non-tuberculous mycobacterium
M. avium intracellulare complex
- Children: pharyngitis, cervical adenitis
- Pulmonary: on top of underlying lung disease
- Disseminated: cytotoxicity, lymphoma
M. marinarum
- From fishes
- Swimming pool granuloma
- Single/clusters of papules/plaques on limbs
M. ulcerans
- Causes Buruli ulcer
- Early: painless nodule
- Progresses slowly, leads to ulceration and scarring
- Rarely fatal but hideously deforming
How are NTMs treated?
Sensitivity testing is important here.
- Clarithromycin
- Rifampicin
- Ethambutol
- +/- amikacin/streptomycin
Name some rapid growing NTMs. How are they treated?
- M. abscessus
- M. cholerae
- M. fortuitum
These cause skin and soft tissue diseases
Treat with a macrolide (with sensitivity testing)
How does TB present?
- Cough +/- haemoptysis
- Fever (with drenching sweats)
- Weight loss
- Malaise
What are the risk factors for primary TB?
- Recent migrant
- HIV +ve
- Homelessness
- Drug user
- Prison
- Close contacts
What are the risk factors for TB re-activation?
- Immunosuppression
- Malnutrition
- Ageing
- Chronic alcohol misuse
How does primary TB present?
This is usually in children, the elderly, or those with HIV. It can be asymptomatic.
The TB multiplies at the pleural surface (a Ghon focus) and can spread to the lymphatic system. The characteristic lesion is a granuloma.
Rare:
- Progressive primary: focus ulcerates into bronchus
- Miliary: disseminated and progressive
How does post-primary TB present?
This is usually in young adults and the upper lobes are affected. It classically has a caseating granuloma in the upper lobe of the lung.
What investigations are ordered for TB?
Imagine:
- CXR
- CT
Culture:
- 3x sputum culture (up to 6 weeks to culture)
- Urine EMU
- Microscopy
Histology:
- Granuloma
Tuberculin skin test (Mantoux)
- Shows previous exposure
- Cross reacts with BCG
- Poor sensitivity
IGRA:
- Antigen specific IFN-gamma
- No BCG reaction
- Does not differentiate between latent and active infection
How is TB treated?
First line:
- Rifampicin
- Isoniazid
- Pyrazinamide
- Ethambutol
RIPE for 2 months, then RI for 4 months
If meningitis RI for 10 months
Second line:
- Quinolones (moxifloxacin)
- Injectables (capreomycin, kanamycin, amikacin)
- Cycloserine
- Ethionamide
- PAS
- Linezolid
- Clofazamine
Resistant TB:
- Mono: resistant to one drug
- Multi resistant: resistant to R and I
- very resistant: resistant to R and I and injectables and quinolones
What are the side effects of TB medications?
Rifampicin:
- Orange secretions
- Hepatotoxicity
Isoniazid:
- Peripheral neuropathy (give B6)
- Hepatotoxicity
Pyrazinamide:
- Hyperuricaemia
- Hepatotoxicity
Ethambutol:
- Visual disturbance (colour vision)
What are examples of extrapulmonary TB?
- Spinal TB
- TB meningitis
- Lymphadenitis
- Pericarditis
- Genito-urinary, renal and testicular
- Abdominal
Describe spinal TB
Also known as Pott’s disease
- fever, sweats, weight loss, back pain
- Haematogenous spread, discitis, vertebral destruction, collapse
Investigation:
- MRI and CT
- +/- aspirate
Treatment:
- One year of anti-TB
Describe TB meningitis
A subacute presentation
- Weight loss, night sweats, fever, meningism
- Lowered GCS, focal neural deficit
Diagnosis:
- CT and LP (lymphocytic)
Treatment:
- One year anti-TB
Describe TB leprosy
Caused by M. leprae and M. lepromatosis
This causes a life long illness with an intubation of up to 10 years.
Presentations:
- Skin: macules, papules, nodules
- Nerves: neuropathy, thickened nerves
- Eyes: keratitis, iridocyclitis
- Bone: periostitis aseptic necrosis
Treatment:
- Rifampicin
- Dapsone
- Clofazimine
