Flashcards in Mycobacteria Deck (21)
Who are the new cases of TB almost always found in in the US?
~65% of the new US cases are among recent US immigrants
What types of TB patients are at highest risk for developing active disease?
AIDS patients — of those who are infected with TB, 10% per year will develop active disease.
• Recently infected with TB (within the past 2 years)
What is the difference between TB infection and disease?
Only a small percentage of those infected will develop active disease with the TB remaining in a latent state instead.
What is the transmission mechanism of TB?
Human to human and is almost exclusively airborne
Who is at most risk for TB?
• Close contacts of an active case
• Foreign-born persons from areas where TB is common
What is the pathogenesis of TB?
TB antigens -> lymphoproliferation, cytokine production, granuloma formation, tissue destruction; positive PPD skin test and Quantiferon assay -> both antimicrobial effect and tissue damage
What is the characteristic histological finding in TB?
Necrotizing granuloma with caseous necrosis. There will be giant cells in the center with palisading epithelial cells
Primary site of infection on x-ray; lung periphery
What is found on exam of TB patients?
Nonspecific symptom complex (cough, fever, fatigue) with possible upper lung field infiltrates on CXR
What is extra pulmonary TB?
TB found in sites that progress from the original, bacteremic phase of infection – brain, epiphyses of long bones, kidneys, vertebral bodies, lymph nodes
What populations is XPTB seen in?
What infections can mimic TB infections?
• Nontuberculous mycobacterial infections
• Fungal infections
PPD skin test reaction
Delayed hypersensitivity response to tuberculin
Essentially an interferon gamma production assay that asks whether the patient’s blood lymphocytes have “immunological memory” for selected TB antigens
What smears for TB will be positive?
Acid Fast Bacillus smears and cultures from otherwise sterile sites
What is the NAAT used for in TB?
Nucleic acid amplification test (NAAT) increasingly available and the standard of practice for rapid diagnosis of TB
What is the origin of nontuberculous mycobacterial (NTM) infections?
NTM infections are environmental (not human) in origin
What do NTM usually require to cause disease?
NTM infections (non-HIV) usually “require” some type of underlying, predisposing lung problem, whereas TB does not require a predisposing condition to cause disease.
structural lung abnormality = predisposing factor
Do NTMs have latency?
NTM do not cause latent infection
Is skin testing and Quantiferon gold useful with NTM infection?