Tuberculosis Flashcards
MTB:
Mycobacterium tuberculosis; a bacteria that causes TB
infection and disease.
TB infection:
A person may develop TB infection upon inhalation of MTB containing coughed droplet nuclei of an active TB patient.
TB disease:
A person with active TB infection that may/may not be able to spread the disease to others. If not treated, the disease can cause death. An outbreak can result from untreated active TB.
Active TB:
A symptomatic form of TB disease that is culture positive for MTB. A person with this type of disease may be infectious and require isolation.
Latent TB Infection (LTBI):
An asymptomatic form of TB infection that is culture negative for MTB. A person with this type of infection has 10% chance of developing TB disease once in their lifetime.
Infectious dose:
TB is an air-borne disease. The aerosol exposure infectious dose of TB is 1-10 MTB bacilli.
Droplet nuclei:
A particle generated by infectious person that can contain 1-3 MTB.
Primary TB:
It presents with hilar enlargement, unilateral parenchymal infiltrates and/or pleural fluid. The linear or alveolar densities are usually small and appear early as small calcified ‘granulomatous’ lesions predominantly in the lower lobes.
Ghon Complex:
It is a pathological indicator of TB disease progression. The lesion in lung is of a granulomatous inflammation and adjacent lymph node.
Miliary TB:
It represents unchecked haematogenous dissemination of mycobacteria resulting in foci either at the time of primary disease or later during reactivation.
Reactivation TB:
It typically presents with infiltrates in the upper lung zones with or without cavitations or with a miliary pattern TB.
Extrapulmonary TB:
TB disease in other human organs (not lungs) such as:
– TBlymphadenitis – PleuralTB
– GenitourinaryTB – Skeletal TB
– MeningealTB – PericardialTB
Describe Tuberculosis Infection & Epidemiology
- TB is #1 cause of death globally due to a bacterial infection.
- One-third of world’s population currently has TB infection.
- People who are immunocompromised such as HIV patients are at risk of developing TB.
- HIV positive patients are 20-30 times more likely to develop active TB. TB is a leading cause of mortality in HIV-positive people.
- Multidrug-resistant TB (MDR-TB) and Extreme drug resistant tuberculosis (XDR-TB) remains a global public health emergency.
- Not all individuals infected with TB will develop symptomatic/active TB. Only 10% of the infected persons will develop TB in their lifetime. Rest 90% remain asymptomatic or what we refer to as latent TB infection.
Describe TB’s risk factors
Those at high risk for developing TB disease:
– HIV positive cases
– Individuals who were infected with M. tuberculosis in the last 2 years
– Children
– Elderly
– Injection drug users
– Immuno-compromised individuals
– Inappropriate and inadequate TB treatment in the past
Facts about Mycobacterium tuberculosis
- Chronic granulomatous disease caused by bacterium Mycobacterium tuberculosis (MTB) with manifestations, involving most commonly the lung but all other organ systems as well
- Aerobic, non-motile bacteria, SLOW GROWING with 20hr doubling time
- 1-4um in length
- Requires specialized media for culture growth.
- Acid fast bacillus with smear morphology showing rods that have specific morphology in liquid media. Cord Factor is responsible for the serpentine cording of MTBC.
- Culture is the gold standard for diagnosis.
- TB is a reportable disease in Canada. Susceptibility testing is mandatory for all culture positive cases.
Cell Wall Core components and functions
Bacteria have a characteristic cell wall, which is thick, hydrophobic, waxy, and rich in mycolic acids/mycolates. Only Mycobacteria have mycolic acids (although Legionella have similar branded chain waxy esters) – like Mycoplasmas with their cholesterol (Borrelia have too). This cell wall makes mycobacteria them impervious to some dyes and antibiotics
Signs & Symptoms
Pulmonary TB:
Symptoms of TB disease depend on where in the body the TB bacteria are growing. TB bacteria usually grow in the lungs (pulmonary TB). TB disease in the lungs may cause symptoms such as
• A bad cough that lasts 3 weeks or longer
• Pain in the chest
• Coughing up blood or sputum (phlegm from deep inside the lungs)
• Weakness or fatigue
• Weight loss
• Lack of appetite
• Chills
• Fever
• Sweating at night
Signs & Symptoms
Extra-pulmonary TB
• Symptoms in other parts of the body depend on the area affected.
What are the TB Diagnostics?
• Tuberculin Skin Test (TST) or Mantoux test
• IGRA (Interferon Gamma Release Assay)
• Chest X-ray
• AFB or Acid Fast Bacilli Smear
• Molecular detection of MTB
• Culture – gold standard
• Identification – sequence based, MALDI-TOF, HPLC, biochemicals etc
• Differentiation between members of MTB complex
• Genotyping
What is the Tuberculin Skin Test (TST) / Mantoux?
- is the standard method of identifying persons exposed/infected with M. tuberculosis.
- An intradermal injection of 0.1 ml of purified protein derivative (PPD) tuberculin containing 5 tuberculin units (TU). Read at 48 to 72 hours after the injection.
- The diameter of the indurated area should be measured. Erythema (redness) should not be measured. Induration of 5mm, >10mm or >15mm noted.
- False-positive or false-negative results
