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Flashcards in Tb Deck (32)
1

Features of mycobacterium

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

2

Spread of tuberculosis

via pulmonary route
inhalation of small of droplets

3

Pathophysiology of tuberculosis

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

4

Immune factors important for containing Tb

T cells
TNF alpha
INF gamma

5

What is a ghon complex?

Parenchymal granuloma and hilar lymphadenopathy

6

Radiological features of primary tb

bilateral hilar lymphadenopathy
middle and lower lobes affected

7

Manifestations of miliary tb

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

8

Mortality of miliary tb

20%

9

Features of reactivation Tb

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

10

Common sites of extrapulmonary Tb

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

11

Tests for latent Tb

mantoux
Quantiferon

12

Limitations of mantoux test

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

13

What does an IGRA (quantiferon) measure?

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

14

Limitations of quantiferon test

less reliable in HIV when CD4 count less than 100
* not affected by non tuberculous mycobacteria or BCG

15

Diagnosis of active Tb

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

16

Issues in treating latent tb

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

Groups who should have screening for latent Tb

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

Treatment of latent Tb

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

19

Treatment of active Tb

Always treat with more than two drugs
RIPE for 2 months, followed by rifampicin and isoniazid for 4 months (total 6 months)

20

Risk factors for relapse of active Tb

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

21

Monitoring of treatment

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

22

Rifampicin ADRs

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

23

ADRs of isoniazid

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

24

What is an important side effect of ethambutol

Optic neuropathy
Red green colour blindness

25

What predicts MDR strain of Tb

Rifampicin resistance

26

What is definition of MDR Tb

Resistant to both isoniazid and rifampicin

27

What is definition of XDR tb

Resistant to isoniazid, rifampicin, fluoroquinolone and an injectable agent

28

BCG vaccination

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

29

Risk of reactivation of TB in HIV patients

5-10% per year

30

Effect of TB on HIV

Increases HIV replication
Accelerates progression of HIV

31

What is IRIS?

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

Treatment of IRIS

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