Mycobacteria

Question 1

Who are the new cases of TB almost always found in in the US?

Answer 1

~65% of the new US cases are among recent US immigrants

Question 2

What types of TB patients are at highest risk for developing active disease?

Answer 2

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)

Question 3

What is the difference between TB infection and disease?

Answer 3

Only a small percentage of those infected will develop active disease with the TB remaining in a latent state instead.

Question 4

What is the transmission mechanism of TB?

Answer 4

Human to human and is almost exclusively airborne

Question 5

Who is at most risk for TB?

Answer 5

• Close contacts of an active case

* Foreign-born persons from areas where TB is common

Question 6

What is the pathogenesis of TB?

Answer 6

TB antigens -> lymphoproliferation, cytokine production, granuloma formation, tissue destruction; positive PPD skin test and Quantiferon assay -> both antimicrobial effect and tissue damage

Question 7

What is the characteristic histological finding in TB?

Answer 7

Necrotizing granuloma with caseous necrosis. There will be giant cells in the center with palisading epithelial cells

Question 8

Ghon focus

Answer 8

Primary site of infection on x-ray; lung periphery

Question 9

What is found on exam of TB patients?

Answer 9

Nonspecific symptom complex (cough, fever, fatigue) with possible upper lung field infiltrates on CXR

Question 10

What is extra pulmonary TB?

Answer 10

TB found in sites that progress from the original, bacteremic phase of infection – brain, epiphyses of long bones, kidneys, vertebral bodies, lymph nodes

Question 11

What populations is XPTB seen in?

Answer 11

AIDS patients

Question 12

What infections can mimic TB infections?

Answer 12

• Nontuberculous mycobacterial infections

* Fungal infections

Question 13

PPD skin test reaction

Answer 13

Delayed hypersensitivity response to tuberculin

Question 14

Quantiferon assay

Answer 14

Essentially an interferon gamma production assay that asks whether the patient’s blood lymphocytes have “immunological memory” for selected TB antigens

Question 15

What smears for TB will be positive?

Answer 15

Acid Fast Bacillus smears and cultures from otherwise sterile sites

Question 16

What is the NAAT used for in TB?

Answer 16

Nucleic acid amplification test (NAAT) increasingly available and the standard of practice for rapid diagnosis of TB

Question 17

What is the origin of nontuberculous mycobacterial (NTM) infections?

Answer 17

NTM infections are environmental (not human) in origin

Question 18

What do NTM usually require to cause disease?

Answer 18

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

Question 19

Do NTMs have latency?

Answer 19

NTM do not cause latent infection

Question 20

Is skin testing and Quantiferon gold useful with NTM infection?

Answer 20

No

Question 21

Do NTM infections disseminate from the lungs?

Answer 21

No, except in the case of AIDS patients