Tuberculosis Flashcards
What causes TB
Infection with Mycobacterium tuberculosis, M.bovis
What is mycobacterium tuberculosis
Obligate aerobe
rod shaped bacteria spread via air-born droplets and dust micro particles
acid fast
slow rate of growth
sensitive to heat and UV radiation
non-motile
What is pulmonary and extrapulmonary TB
pulmonary - lungs
extrapulmonary - other body parts
Where is the TB situation the worst
Africa
half of all HIV infected adults infected with M.tuberculosis
What are the less frequent causes of TB
M.bovis
M.africanum
What is used in the BCG vaccine
attenuated M.bovis
Why has TB not been eradicted
Global burden
Laten TB infection
Drug resistance
Social determinants of health
Co-infection with HIV
Diagnostic challenges
Stigma and lack of awareness
Inadequate healthcare infrastructure
Migration
Who are at high risk of TB
-recent TB infection
-weakened immune system
Risk factors for TB
Low socio-economic status
Diseases that weaken the immune system like HIV, cancer
Person on immunosuppressant like steroids
Migration from a country with high cases like West Africa
Malnutrition
Crowded living conditions
Substance abuse like alcohol and drug abuse
Healthcare workers
Smoking, exposure to silica dust
Medications like TNF and cancer drugs
Latent TB infection
-no signs or symptoms
-host defences prevent growth of bacteria (macrophages engulf bacteria)
-not infectious
-skin or blood test positive
-normal chest x-ray
TB disease
-primary infection
-signs and symptoms present
-spread infection
-skin or blood test positive
-abnormal chest x ray or sputum sample
Methods of TB diagnosis
-Tuberculin skin test (TST)/Mantoux
-Inferon-Gamma Release Assay (IGRA)
-Chest X ray
-Sputum smear microscopy
-Molecular testing (PCR/Nucleic Acid Amplification Test (NAAT)
-CT scan
-Bronchoscopy and thoracenthesis
-Biopsy
What is the Tuberculin Skin Test (TST)
Inject 0.1ml of purified protein derivatives (PPD) under the forearm
measures induration (raised area)
positive test = 5mm or larger
does not differentiate between latent and active TB
What are the limitations of the Mantoux test
false positive results due to prior BCG vaccine and exposure to non-tuberculosis bacteria (atypical mycobacteria)
false negative due to weakened immune system/malnutrition and viral infection
TST results
> 5mm (HIV positive/recent TB/organ transplant)
10mm (recent arrivals from high prevelance countries/IV drug users)
15mm (no known risk factors)
Interferon gamma release assay
detect release of IFN-gamma
preferred to TST (quantitative)
blood drawn contains antigens associated with M. tuberculosis
amount of IFN gamma released by stimulated WBCs measured
T lymphocytes release gamma interferon
What does a chest x ray reveal
Infiltrates (areas of increased density)
Nodules
Cavities
Consolidations (areas of lung tissue filled with fluid or
cellular material)
Lymph node enlargement: visible on the X-ray as round or
oval-shaped densities
Pleural effusion: seen as a hazy area or blunting of the
normally sharp angle between the lung and chest wall
Sputum smear microscopy
detects acid-fast bacilli (AFB)
sputum to create thin smear
stained using Ziehl-Neelsen
Bright red rods against blue/dark background
PCR and NAAT
PCR amplifies specific component of DNA NAAT (amplifies D)
diagnoses specific Mycobacterium
very expensive
NICE - request if suspicion of pulmonary TB/HIV/need for large contact tracing
Symptoms of TB
A persistent cough
Constant fatigue
Weight loss
Loss of appetite
Fever
Coughing up blood
Night sweats
primary stage of TB
asymptomatic/ mild flu like symptoms
reactivated TB
takes months to appear
gradual onset of anorexia, weight loss, fever, night sweats
TB affecting the lung
Persistent cough lasting longer than 3 weeks. Sputum (mucoid
then purulent); containing bacilli if cavitation occurs, haemoptysis
Systemic TB
headache and neurological deficit in brain metastasis, swelling in neck if lymph involvement
