Tuberculosis Flashcards
(118 cards)
What global areas have the highest incidence of TB?
Sub-Saharan Africa
West Africa
South East Asia and the Pacific
How many people world wide likely have latent TB?
1-2 billions
How many cases of TB are diagnosed annually?
10 million
How many people die each year from TB?
1.6 million
What is the Ro number of TB
<1 - 3 (appears that some people are super spreaders)
What bacterium causes TB?
Mycobacterium Tuberculosis
**ABout 5% of cases are caused by Mycobacterium Bovis
What is the bacteriology of M. Tuberculosis?
Gram Postive
Acid Fast Bacillus
Slow growing (17h) —> difficult to culture
** CAN MAKE IT GROW FASTER BY USING A LIQUID MEDIUM
How does M. Tuberculosis spread?
Aerosol
**Note that only active pulmonary is contagious
What are risk factors for developing active TB?
HIV Co-infection
DM
Smoking
TNF-a
Vitamin D Deficiency
ETOH XS
What is the pathophysiology of TB?
Aerosolised Bacilli enter into the bronchi –> alveoli where they invade into phagocytic cells
Within phagocytic cells two things can happen:
1. Immune system not strong enough to mount a full response against M.Tuberculosis –> active TB
- Immune system has a delayed type response to TB bacteria and causes large amounts of inflammation as phagocytic cells are destroyed. This leads to scarring and granuloma formation. Un-destroyed phagocytes protected within the granuloma are responsible for re-activation disease
**The granuloma illustrates the duality of M. tuberculosis infection: from the host’s perspective, the granuloma is a bacterial ‘prison’ with the potential to ‘wall off’ infection from the rest of the body; however, from the bacterial perspective, it is a growing collection of phagocytic cells to infect and replicate within.
What percentage of people with TB go on to have active infection?
5-10%
How does Classic TB Present?
Chronic productive cough not responding to standard Abx
Weight loss
Pyrexia
Night sweats
Lymphadenopathy (infected macrophages can move through the blood and into lymph nodes)
Fatigue
Haemoptysis
What are common sites of Extra Pulmonary TB (EPTB)?
Neuro
Spinal
Bony
Renal
Skin
What is the difference between TST and IGRA?
TST –> looks for immune response in skin due to secodnary immune response from current or previous TB infection
IGRA –> Blood test looking at serum response to TB by checking IFNy levels
Basically IFNy is released in peripheral t-cells of people who have been exposed to TB; only useful in detecting LTB because there is a high false negative rate of IGRAs in active TB (probably due to general immune changes and therefore low T cell levels in circucating peripheral blood)
should add that IGRA isnt useful in kids <5 and that it was created to try and replace the TST which has many false negatives
How is TB diagnosed?
Sputum Culture and Microscopy (ZN Stained, Fluroscein)
Gene X-pert
Urinary LAM (if HIV +ve)
CXR
IGRA / mantoux test
Gastric Aspirates (paeds)
How can you diagnose latent TB infection (LTBI)
IGRA or TST
What are the standard medications used in uncomplicated TB?
Rifampicin
Isoniazid
Ethambutol
Pyrazinamide
What is the epidemiology of TB + HIV co-infection?
Active TB is 20-40 times higher in HIV +ve people due to early loss of alveolar CD4 cells
9% of global active TB infections are in HIV +ve people
How does DM impact TB outcomes?
Increased mortality
Increased risk of relapse
What percentage of TB cases occur in children?
10%
How has COVID-19 impacted the epidemiology of TB?
Significant reduction in case recogition –> now increasing numbers of diagnoses and deaths from TB due to missed early infections
What are the three main aims of the WHO END TB strategy
- 50% reduction of TB by 2025
- 75% reduction of deaths from TB by 2025
- 0 people living with catastrophic financial burdens due to TB
Are we close to achieving the goals of the WHO END TB strategy by 2025?
NO - not even close
What are the sensitivity and specificity of ZN stained smear microscopy in TB?
Sensitivity = 60-70%
Specificity = >90%