Tuberculosis Flashcards
What is mycobacterium tuberculosis (MTB)?
- pathogenic bacteria
- aerobic bacteria hence why they affect the lungs
- can be Gram - or + due to waxy cell coating
- generally classed as - though
What is atypical non-mycobacteria?
- part of mycobacterium family (cousin of TB)
- opportunistic bacteria
- effect immunocompromised patients
TB is the most common cause of infectious related mortality disease worldwide. Approximately how many people worldwide have latent TB?
- 2.3 billion - global incidence is falling
Is there an interaction between TB and HIV?
- yes, TB affects those immunocomprimised
- HIV patients have low CD4+ T cells
- HIV patients are unable to mount an immune response
- always test for HIV when suspecting TB
TB rates are reducing, but still have a high incidence in some places, especially those with low socio-economic countries. What is the definition of high incidence?
- 40 per 100,000
Why is TB more common in big cities?
- ⬆️ ethnic diversity - people acquire TB and move to UK - majority of TB patients in UK, are born outside UK
Which patients are at greater risk of developing TB?
- deprivation (malnourished, overcrowding) - alcohol - prisons - immunocompromised - elderly - high risk groups (jobs)
How is TB transmitted?
- through airways (80% affects lungs)
Once inside the lungs how can TB spread through a specific type of immune cell?
- macrophages ingest TB and attempt to phagocytose
- if macrophage cannot phagocytose TB can replicate in endosome
What amount of the worldwide population have latent TB?
- 1/3 - 10% of this 1/3 will develop active TB
If TB becomes active and is not contained it can spread to the rest of the body, what does haematogenous mean?
- infection spread through blood
If TB becomes active and is not contained it can spread to the rest of the body, what system other than circulatory can it used to spread?
- lymphatic system - can enlarge lymph nodes
In addition to spreading through lymphatics and blood, how else can TB spread?
- direct contact - pericardium could be affected
What are common clinical presentations of pulmonary TB?
- THINK TB
- cough (not improving with antibiotics)
- haemoptysis (coughing up blood)
- chest pain and breathlessness
- fever / night sweats
- fatigue and weight loss
What does the mnemonic THINK TB when diagnosing TB mean?
- T = troublesome cough
- H = haemoptysis
- I = involuntary weight loss
- N = night sweats and fever
- K = known exposure to TB
- T = tiredness
- B = breathlessness and chest pain
What other disease does TB present clinically similar to?
- sarcoidosis
What is erythema nodosum commonly seen in TB and Sarcoidosis?
- erythos = greek for red - red and raised tender rash on the skin (generally legs) - acute presentation
What is Phlyctenular conjunctivitis commonly seen in TB and Sarcoidosis?
- red and inflamed eye
When a patient is comes into contact with TB and acquires it, macrophages digest and try to phagocytose it. Following this is can become one of 2 things, what are they?
- active - latent
If TB becomes latent what are the 2 things that can occur?
- lungs heal and eradicate TB
- re-activation when patient is immunocompromised
If a patient becomes infected with TB that the immune system is not able to develop a granuloma, what happens in the short term to the patient?
- TB symptoms present
- TB can then disseminate to lungs
- TB can spread to the whole body (miliary)
What is the granuloma surrounding the TB infection called?
- Ghon Focus
- small foci on lungs
In addition to forming a Ghon foci (granuloma) where else can then granuloma overlap to or immune cells spread the TB?
- lymph nodes at the hilum primary bronchi enter lungs
- these lymph nodes become inflamed
If the Ghon foci overlap onto a hilar lymph nodes, what is this complex called?
- Ghon complex
What is the term given to the tissue within the granuloma surrounding the TB?
- necrotic tissue (dead)
- caseous necrosis (cheese like)
What happens to Ghon complex that allows them to be identified on chest X-rays?
- undergo fibrosis and/or calcification
- this can be seen on an X-ray, called a Ranke complex
When TB is surrounded by the granuloma, do they always die?
- some can die
- some remain latent
If the acute TB infection cannot be surrounded by a granuloma, what can happen to the infection?
- disseminate (spread) throughout lungs
- it can can spread to whole body, called miliary TB
What does miliary TB mean?
- TB infection has spread systemically to whole body
Out of all people who are exposed to TB, what % will develop a primary and latent infection?
- primary = 5%
- latent = 95%
Of the 95% who develop a latent infection, what % will develop no disease and have a reactivation of TB?
- 90% will have no disease
- 5% will have re-activation of TB
Prednisolone is a corticosteroid given to patients with sarcoidosis. Why should this not be given to patients with an acute TB infection?
- it can enhance spreading
Why is reactivation of TB dangerous?
- disseminate to whole body (miliary dissemination)
- it can be transmitted to others
If TB is re-activated memory T cells are activated secreting cytokines. Instead of forming granulomas, TB creates something else, what is the term given to this?
- cavity formation
- gas filled space ⬆️ dissemination in lungs
- called cavitary TB
What is pulmonary TB?
- active TB
- ⬆️ cavitary = ⬆️ contamination to others
- ⬆️ risk of dissemination in lungs and miliary (whole body)
What shape can TB be classified as, shape wise?
- bacillus (rod shaped)
Is TB aerobe or anaerobe?
- aerobe, hence why is likes the lungs
Is TB Gram - or +?
- is partially both
- but generally classed as slighlty negaitve
Does TB possess a cell wall?
- yes
- gives bacterial its waxy surface (mycolyic acid)
- but no phospholipid outer membrane
Does TB divide quickly or slowly?
- slowly
- every 16-20 hours
If a patient is suspected of having TB and respiratory symptoms, what is commonly the first scan that is performaed?
- chest X-ray
What is a sputum test?
- sputum is collected from patient
- bacterial culture on sputum is performed
What is bronchoalveolar lavage?
- bronchiole tree is washed - fluid is collected and investigated
What is the Mantoux (tuberculin test) test?
- skin tests
- patient is injected intradermally with tuberculin (part of TB)
- if patient has been exposed to TB they will have an immune reaction within 48-72 hours
- large area = POSITIVE test
What classification of hypersensitivity is a positive reaction to the Mantoux (tuberculin test) test?
- delayed hypersensitivity type IV (delayed type IV)
- APC (macrophages) originally present antigen to T cells
- T cells form memory and effector cells, preparing the immune system for 2nd exposure
- once 2nd exposure memory T cells activate APC (specifically macrophages)
What is the Interferon gamma (a soluble cytokine) release assay (IGRA)/T-spot test for TB?
- blood sample taken
- IGRAs are detected in the blood specific to TB
- POSITIVE tests tells us if patients has had TB
Does BCG vaccine (vaccine which protects against TB) affect the results of the Mantoux and Interferon gamma release assay (IGRA)/T-spot test?
- yes - BCG would show positive on Mantoux test
- BCG does not affect IGRA T spot test, so this is preferred test
Are Mantoux (Tuberculin test) and Interferon gamma release assay (IGRA)/T-spot test able to distinguish between active and latent TB?
- no
The acid fast stain can be used when trying to diagnose TB. TB does not stain well in gram staining, due to the mycolic acid content that make up its waxy walls. What does the acid bind with on TB and what colour will TB appear?
- bacillus retains stains following acid treatment
- dye binds to mycolic acid
- appears pink or red
The Ziehl-Neelson Acid based stain is a fast acid stain, what is the basic principles of how to run the test?
- sample is fixed to plate and heated
- treated with acid
- dye added
- pink/purple = acid fast bacteria
- blue = non acid fast bacteria
On the Ziehl-Neelson Acid based stain what colour will TB and non mycobacterium appear?
- red/pink on blue background
- no distinguishing between TB and non-TB though
- all myobacterium family contain mycolic acid
What 2 things can be done on a sputum samples when trying to diagnose TB?
- TB bacterial growth
- antibiotic sensitivities
We can take samples from other areas to try and confirm a diagnosis of TB. What are the bodily fluids that are sampled?
- pleural fluid (TB can spread to pleural space)
- urine (sugars from TB can be detected)
- cerebrospinal fluid
What is central necrosis caseation in an acute TB infection?
- necrotic (dead) tissue
- contained with granuloma, can then becom latent
Where can acid fast bacilli in acute TB infections be found inside the lungs, and what are they surrounded by?
- generally in upper lobes
- surrounced by granulomas
In the Mantoux (Tuberculin test) and Interferon gamma release assay (IGRA)/T-spot test, what is the cell type of the adaptive immune response required?
- memory T cells
Is the Mantoux (Tuberculin test) or Interferon gamma release assay (IGRA)/T-spot test more specific?
- Interferon gamma release assay (IGRA)/T-spot test
- unaffected by BCG
When trying to make a clinical diagnosis of TB, what is the common clinical diagnosis pathway?
- exposure to TB
- signs and symptoms of TB
- abnormal X-ray
- positive Mantoux / IGRA test
- culture
Are TB symptoms present in both latent and active TB?
- active = yes - latent = no
When analysing sputum samples will TB be present in active and latent TB?
- active = yes
- latent = no
In TB, how long does it take sputum samples to be cultured, and will active and latent TB come back positive?
- takes 6-8 weeks
- active = TB present
- latent = TB not present
In TB will X-rays be normal in active and latent TB?
- active = abnormal - latent = normal
In the Mantoux (Tuberculin test) and Interferon gamma release assay (IGRA)/T-spot test, do they both test positive for TB in acute and latent TB?
- positive for both latent and active
In a patient with TB are both latent and acute TB infection to other people?
- active = yes
- latent = no
Is bilateral hilar lymphadenopathy specific to TB or sarcoidosis?
- present in both - B symptoms
What is the standard treatment for a patient with an acute TB infection in the first 2 months?
- initial phase fully sensitive TB
- standard quadruple therapy
- 4 drugs given together
What is the standard treatment for a patient with an acute TB infection in the last 4 months of a 6 month standard treatment regime?
- continuous phase fully sensitive TB - 2 drugs are given
What is the main risk of not giving the patient the correct type and dose of drugs?
- multi drug resistant TB - normally due to poor adherence - multi drug resistant TB can be transmitted
In patients with multi drug resistant TB, what is the danger to public health?
- high risk of contamination - patients are normally isolated - given longer dose of antibiotics
What is the effectiveness of treatment in TB?
- it is curable
What is an index case?
- person who got TB
When screening for latent TB who needs to be screened?
- close contacts of index case - pre-employment in healthcare
If a patient has latent TB, how is this treated?
- 3 months of Rifampicin and Isoniazid OR - 6 months of Izoniazid
If a doctor arrives to work for the NHS in the UK and is healthy and fine, has a normal X-ray but a positive IGRA test, what treatment would be required?
- positive IGRA indicates latent TB - 3 months of Rifampicin and Isoniazid OR - 6 months of Izoniazid
Which of these is a risk factor for developing active TB? 1 living in low altitude 2 male gender 3 malnutrition 4 obesity 5 smoking
- malnutrition
