10 - Tuberculosis Flashcards
What 2 types of populations have a higher incidence of Tb in Canada?
- Canadian-born Aboriginal
- Foreign born
What province/territory has highest incidence of Tb ?
North (the territories)
What bug causes Tb?
Mycobacterium tuberculosis
Describe Mycobacterium tuberculosis
- bacillus
- aerobic and anaerobic, intracellular and extracellular
- slow growing, latent, dormant states
- multi-drug resistance
**using 1 drug to treat Tb is not effective
Describe the transmission of Tb
- communicable disease, aerosolized droplets
- enters bronchioles and alveoli, settles in lower lobes
- first-line macrophage-mediated immunity
- followed by T-cell immunity over 2-8 weeks
What are the risk factors for Tb?
- close contacts especially laryngeal or pulmonary TB (positive smear/culture stages)
- endemic areas (Northern Canada)
- poor or crowded living conditions, homelessness, correctional facilities
- healthcare workers
Of those who get the initial infection, how many develop the disease and how many have a latent Tb infection?
5% have primary disease
95% have latent TB infection
Of those who have the latent TB infection, how many will have a reactivation and how many will have no disease?
5% will have a reactivation of Tb
90% will have no disease
Describe a latent TB infection?
- asymptomatic or mildly symptomatic, non-contagious
- normal X-ray, negative sputum stain and culture results
- lymphatic spread to regional nodes, lung apices .. less commonly bone marrow, liver, spleen, kidney, meninges
- latent or dormant in seeded foci (Ghon nodes) for months to years
How do we diagnose a latent Tb infection?
1) TST (Tuberculin skin test)
- heat sterilized, purified protein derivative
- delayed T-cell hypersensitivity response, induration within 48-72 hours
- false negative results if cutaneous anergy (pre-conversion, neonate, elderly, HIV, lymphoma, chemotherapy, corticosteroids); use positive control mumps or Candida
- does not distinguish latent from active disease !!!!, other mycobacterial infection or prior BCG vaccine
2) IGRA - interferon gamma release assay
- blood test measures T-cell release of IFN-gamma
- does not distinguish latent from active disease; more specific than TST in patients vaccinated with BCG
What does a TST result > 10 mm mean?
TST conversion (within 2 years)
In people who have been exposed to Tb in the past 2 years, they are at a higher risk of it becoming active. If you give them prophylaxis, you can reduce activation by ____%.
90%
What is the treatment for latent TB infection?
INH daily x 9 months
What is an alternative treatment for latent TB infection?
RMP daily x 4 months
INH and RMP are both associated with ______
hepatotoxicity
Primary TB:
Early progression typically within ____ months of exposure
4-12
Primary TB:
Risk factors?
- age
- immune function
Primary TB:
Most common in ?
lymph node or pleural disease
in lungs
Primary TB:
Disseminated including CNS more common in ?
infants, immunocompromised
Reactivation TB:
Late progression ____ months or longer after exposure
18-24
Reactivation TB:
Most common upper lobe pulmonary disease (_____)
pneumonia
Reactivation TB:
Extra-pulmonary more common in _______
immunocompromised
What are some high risk factors for active TB infection ?
- AIDS/HIV
- Transplant
- Lung disease (silicosis)
- Hemodialysis
- Carcinoma in head and neck
- Recent TB infection in the past 2 years
- Abnormal chest x ray
Clinical signs and symptoms of active Tb ?
- dry then productive cough > 2 weeks
- hemoptysis (coughing up blood), chest pain
- fever, night sweats
- anorexia, weight loss (advanced disease)
