Tubercolosis Flashcards
Why do mycobacteria need to be stained with acid fast stain
Thick waxy cell wall prevents other stains being effective
What is the main TB causing mycobacterium
M. Tuberculosis
Do all mycobacteria cause TB
No
How many mycobacteria species cause TB
5
TB risk factors
Non UK born/ recent migrants from S Asia or sub Saharan Africa
HIV
Immunocompromised
Homeless
Drug use
Prisoners
Close contacts of TB
young adults
Elderly
What airborne particles transmit TB person to person
Droplet nuclei
How is TB spread
Inhaling droplet nuclei
Fomites
What actions/behaviours increase TB spread
Cough
Sneezing
Speaking
Singing
What affects the probability TB will be transmitted
Infectious mess of person with active TB
Environment exposure occurred
Exposure length
Virulence of tubercle bacilli
Host immunity
Host Co morbidities
How can TB transmission be prevented
Isolate infected people
Quick Effective treatment
Which area of the lungs do inhaled TB bacteria usually settle in
Sub pleural area of mid or lower lung zones
What happens to inhaled TB bacteria once settled in the lung
Engulfed by alveolar macrophages -> Ghon focus formed -> TB laden macrophages travel to local lymph nodes -> Ghon complex formed -> active primary disease or initial containment
Ghon focus
Primary lesion caused by mycobacterium bacilli
What are the 3 possible outcomes of inhaling TB bacteria
Progress to primary active disease
Heals or effectively contained and stays latent
Initially contained then reactivates later - post primary TB
What is post primary TB
Initially contained latent infection reactivated
How does the immune system react differently to post primary TB than primary TB
Memory cells allow faster response, but immune system can overreact causing complications
What % of people infected with Tb will never develop active disease
90
TB infection
Presence of MTB in body - active or latent
Does not mean the person has TB disease
TB active disease
Symptomatic Infection
MTB latent infection
Living dormant MTB in body with no symptoms
What is the biggest risk factor for latent TB reactivating
HIV
How can latent TB be prevented from reactivating
Diagnosis
Chemoprophylaxis
TB reactivation risk factors
HIV infection
Substance abuse
Prolonged corticosteroid therapy
Immunosuppressive therapy
Tumour necrosis factor alpha antagonists
Organ transplant
Haematological malignancy
Severe kidney disease / haemodialysis
Diabetes mellitus
Silicosis
Low body weight
What condition is tested for in all suspected and confirmed TB cases
HIV
What are the 3 types of TB
Pulmonary Tb
Extra pulmonary TB
Miliary TB
Where does pulmonary TB occur
Lungs
Where can extrapulmonary TB occur
Larynx
Lymph nodes
Pleura
Brain
Kidneys + adrenals
Bones
Joints
Which groups is extrapulmonary TB more common in
HIV infected
Immunosuppressed
Young children
Where does miliary TB occur
Bloodstream - carried to all parts of body
What is the rarest type of TB
Miliary
Features of characteristic TB lesion/ tubercle
Spherical granuloma with central caseation
What type of reaction is caused by MBT ingested by macrophages in primary TB
Granulomatous reaction
What cells surround the caseous necrotic core of a primary TB tubercle/lesion
Epithelioid macrophages
Langhans multi uncleared giant cells
Lymphocytes
What makes up the caseous necrosis in the centre of a primary TB tubercle
Calcified cellular debris, dead MTB, and dead macrophages
What type of lesions are caused by primary TB
Spherical granuloma
What type of lesion is caused by post primary TB
Cavitary lesions
Why do post primary TB cavitary lesions usually form in upper lung lobes
Better oxygenation aids aerobic MTB
Are MTB aerobic or anaerobic organisms
Aerobic
Pulmonary TB symptoms
Fever
Night sweats
Weight loss + anorexia
Tiredness
Malaise
>3 wks cough
Haemoptysis
Dyspnoea
What is the most common pulmonary TB symptom
Cough lasting 3+ wks
Pulmonary TB signs
Pyrexia
Crackles in affected areas
Hyperesonnance
Decr lung expansion
Signs of pleural effusion
How does pulmonary TB cause hyper resonance
Cavitation in severe disease
How does pulmonary TB decrease lung expansion
Fibrosis in severe disease
Which investigations are used to diagnose active pulmonary TB
Chest x ray
Microbiology - sputum / induced sputum broncho alveolar lavage fluid samples
Histology
How does TB appear on CXR
Defined patchy consolidation
Cavitation
Fibrosis
Pleural effusion
Disadvantages of TB microscopy
Can’t differentiate MTB from non tubercolosal mycobacteria infection
Can’t differentiate live and dead bacteria
May be negative even in active disease
Why might microscopy for a patient with active TB still come up negative
Early disease
Specimen collection technique
Poor cough reflex
HIV AIDS
What is the gold standard for TB diagnosis
Culture
What test must be done before a suspected TB case can be declared negative
Culture must come back negative
Why are both solid and liquid media used in a Tb culture
Liquid faster
Solid more sensitive
Which test can be used to detect multi drug resistant and extrpensively drug resistant TB in smear samples
Nucleus acid amplification tests
What group receives the BCG vaccine
Babies in high prevalence communities
New entrants from high risk areas
Health care workers
Close contact ps of active respiratory TB
How does protection from BCG vaccine change over time
Decrease over time
Little evidence for protection in adults
How is latent pulmonary TB diagnosed
Tuberculin sensitivity test
Interferon gamma assays
What does the tuberculin sensitivity test measure
Cell mediated immune response
How is the tuberculin sensitivity test carried out
Tuberculin injected Intradermally and induration measured 48-72 hrs later
How is tuberculin injected in tuberculin sensitivity test
Intradermally
Can the tuberculin sensitivity test and interferon gamma assays distinguish between latent and active MTB infection
No
What does an interferon gamma essay measure
Interferon gamma - Cell mediated immune responses of T cells to MTB antigens
Are sputum smears and cultures positive or negative in a person w latent TB
Negative
Is latent Tb infectious
No
Latent TB first line treatment
Isoniazid + pyridoxine/ vit B6
Isoniazid + pyridoxine + rifampicin
Why should active Tb not be treated with a single drug
Increase drug resistance
How many drugs are used in standard active TB treatment
4
First line active TB drugs
Rifampicin
Isoniazid
Pyrazinamide
Ethambutol
RIPE
Second line active TB drugs
Quinolones
Injectable capreomycin, kanamycin, amikacin
Ethionamide/prothionamide
Cycloserine
PAS
linezolid
Clofazamine
Rifampicin side effects
Incr transaminases - liver enzyme
Affects other drugs inc oral contraceptive
Orange secretions
Isoniazid side effects
Peripheral neuropathy - pyridoxine/b6 prevents
Hepatotoxicity
Pyrazinamide side effects
Hepatotoxicity
Ethambutol side effects
Visual disturbance
Why is pyridoxine given with isoniazid
Prevents peripheral neuropathy from isoniazid
How long is TB treatment if no drug resistant suspected
6 months
How is TB treatment adherence ensured
Directly observed theraoy
Video observed therapy
Why is TB treatment adherence supervised
Prevent transmission
Lots of pills and side effects makes non adherence likely
Multi drug resistant TB
Resistant to rifampicin and isoniazid
Extremely drug resistant TB
Resistant to rifampicin, isoniazid, fluroquinolones, + 1+ injectable
Why does Miliary tb affect multiple organs
Bacilli spread through blood
How can extrapulmonary TB reach the gut
Swallowing tubercles in coughed up mucous
Where does extra pulmonary TB occur in Potts disease
Spine
Types of extrapulmonary Tb
Lymphadenitis
Gastrointestinal
Genitourinary
Bone + joint
Tuberculous meningitis
When should TB be notified
Any suspected or made diagnosis
Which group is BCG vaccine not effective in
HIV
Why should people with HIV not receive the BCG vaccine
Not effective with HIV
prevents future use of tuberculin sensitivity test
What could cause a positive tuberculin sensitivity test in a person without TB infection
Preciously received BCG vaccine
