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Infectious Disease > Tb > Flashcards

Tb Flashcards

1
Q

Features of mycobacterium

A 
Intracellular bacteria
slow growth rate
Growth increases with oxygen
waxy cell wall
weakly gram positive
identified with ziehl nielsen stain
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2
Q

Spread of tuberculosis

A

via pulmonary route

inhalation of small of droplets

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3
Q

Pathophysiology of tuberculosis

A

taken up by macrophages which can’t break it down
bacteria replicate inside cell
formation of granuloma
cell mediated response occurs at 2-8 weeks

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4
Q

Immune factors important for containing Tb

A

T cells
TNF alpha
INF gamma

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5
Q

What is a ghon complex?

A

Parenchymal granuloma and hilar lymphadenopathy

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6
Q

Radiological features of primary tb

A

bilateral hilar lymphadenopathy

middle and lower lobes affected

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7
Q

Manifestations of miliary tb

A 
pulmonary - dyspnoea, cough, CP
fever, night sweats
enlarged LN
bone/joint
GI involvement
CNS signs
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8
Q

Mortality of miliary tb

A

20%

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9
Q

Features of reactivation Tb

A

insidious onset of weight loss, fever, night sweats, chest pain, cough
CXR - fibrocavity changes in upper lobes

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10
Q

Common sites of extrapulmonary Tb

A

lymph nodes - 40%
pleura - 20%
GU/skeletal/cerebral - rarer

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11
Q

Tests for latent Tb

A

mantoux

Quantiferon

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12
Q

Limitations of mantoux test

A

false negative in immunosuppressed and overwhelming Tb as relies on cell mediated immunity
false positives in non tuberculous mycobacteria and BCG vaccine

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13
Q

What does an IGRA (quantiferon) measure?

A

T cell release of interferon gamma in response to stimulation by highly specific Tb antigens

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14
Q

Limitations of quantiferon test

A

less reliable in HIV when CD4 count less than 100

* not affected by non tuberculous mycobacteria or BCG

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15
Q

Diagnosis of active Tb

A

Don’t use quantiferon or mantoux in actuve disease
Visualisation of acid fast bacilli under microscopy (provides measure of infectivity)
Culture is gold standard (slow to grow 10-14 days)
Nucleic acid amplication - rapid test + provides information on rifampicin resistance

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16
Q

Issues in treating latent tb

A

dont test unless will treat
5% latent tb becomes active in first 18 months
then 5% lifetime risk of reactivation
risk of isoniazid hepatitis increases with age – therefore need to balance risk with benefit

17
Q

Groups who should have screening for latent Tb

A

High risk of reactivation
- HIV, transplant, chemotherapy, lymphoma, leukaemia, silicosis, renal dialysis, TNF-a

Increased risk of new infection

  • close contact of active tb individual
  • healthcare workers with high exposure
18
Q

Treatment of latent Tb

A

treatment decreases risk of active Tb by 90%
isoniazid for 9 months
make sure to exclude active disease with symptoms and CXR

19
Q

Treatment of active Tb

A

Always treat with more than two drugs

RIPE for 2 months, followed by rifampicin and isoniazid for 4 months (total 6 months)

20
Q

Risk factors for relapse of active Tb

A

Cavitation
Extensive disease
Immunosuppression
Positive sputum culture after 8 weeks of treatment

21
Q

Monitoring of treatment

A

Sputum - average time to smear negative 3-4 weeks
Bloods for monitoring toxicity
Adherence with DOT

22
Q

Rifampicin ADRs

A 
GI upset
rash
Thrombocytopenia
Haemolytic anaemia
Colours body fluids red/orange
Small risk of hepatitis
23
Q

ADRs of isoniazid

A

Peripheral neuropathy - can be reduce with pyridoxine administration
Hepatitis (can be severe, increases with age and underlying liver conditions)
GI upset
Rash
Seizures

24
Q

What is an important side effect of ethambutol

A

Optic neuropathy

Red green colour blindness

25
Q

What predicts MDR strain of Tb

A

Rifampicin resistance

26
Q

What is definition of MDR Tb

A

Resistant to both isoniazid and rifampicin

27
Q

What is definition of XDR tb

A

Resistant to isoniazid, rifampicin, fluoroquinolone and an injectable agent

28
Q

BCG vaccination

A

Given to infants in endemic Tb countries
Efficacy 50%
Prevents disseminated disease and meningitis in children
Live vaccine

29
Q

Risk of reactivation of TB in HIV patients

A

5-10% per year

30
Q

Effect of TB on HIV

A

Increases HIV replication

Accelerates progression of HIV

31
Q

What is IRIS?

A

paradoxical worsening of Tb due to increased effectiveness of immune system
occurs 1-3 months after commencement of ART
more common if lower CD4 count and extrapulmonary disease

32
Q

Treatment of IRIS

A

Steroids and symptomatic treatment

To prevent IRIS - initiate ART 4-8 weeks after Tb treatment

Infectious Disease (8 decks)

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