Introduction to mycobacteria II

What increases the risk for reactivation of TB disease?

1. HIV infection

2. Diabetes

3. Renal failure

4. Malnutrition

5. Certain cancers

6. Alcohol overuse

7. Cigarette smoking

8. Medical therapies that impair immune function

What can reactivation of TB disease lead to?

1. Respiratory TB disease

2. Non-respiratory TB disease

Is TB mostly pulmonary disease? What percentage of cases are extra pulmonary? What percentage are from milliary?

Yes it is and 15-20% are extra pulmonary while 2% are milliary

What does milliary mean?

This is a form of tuberculosis that spreads throughout the body via the bloodstream and forms tiny seed like lesions in various organs

Can TB affect any body system?

Yes

What is the major site of infection for TB disease? What follows this?

1. Lymph nodes

2. Gastrointestinal

What are the three clinical manifestations of TB with associated percentages?

1. Primary disease (5-10%)

2. Reactivation (90-95% of disease)

3. LTBI (90% of all TB infections)

What are the symptoms associated with primary disease?

1. Fever (70%)

2. Pleuritic chest pain

3. Fatigue

4. Cough

5. Arthralgia

What are the symptoms of reactivation?

1. Cough, weight loss, and fatigue in 1/2-2/3

2. Nigh sweats in 1/2

Chronic symptoms

What are the symptoms associated with LTBI?

Asymptomatic

How can we figure out if a patient has TB?

1. Based on if they have a history of TB (treated or not)

2. Possible exposure history based on immigration from country that is endemic, contact with known case, or work related

How is active TB diagnosed?

1. Through clinical manifestations

2. Radiographic imaging

3. Lab

What radiographic imaging can be performed? What can this identify?

1. CXR

2. CT

3. Other directed imaging

This can identify granulomas, cavitation, and apical pneumonia

How can we diagnose in a lab? What is the specimen for collection?

Specimen is sputum or tissue. Can perform microscopy (acid-fast), culture (BSL 3 lab), and molecular (PCR)

How long do you have to wait to report a negative culture result for TB?

6-8 weeks

How can we culture TB?

1. Solid media to look for colony morphology using Lowenstein Jensen medium

2. Agar based using middlebrook 7H10 or 7H11

3. Liquid media using MGIT (mycobacterial growth indicator tube) or middlebrook 7H12

What is an advantage of using liquid culture? Disadvantage?

It is faster but it is unable to detect mixed culture

What is the most common/least expensive way to diagnosis latent TB?

Tuberculin skin test (TST) using purified protein derivative

What does TST require?

A skilled health care worker and have to return in 72 hours

Why would a false positive be propagated in TST? What about a false negative?

False positives occur because of BCG vaccine history. False negatives can occur because of active/early TB or immune suppression

What would a positive result be in TST?

Induration of greater than 10 mm with erythema

What is the result when there is induration of 5-9 mm after TST?

The patient has low level sensitization with the tubercle bacilli or cross reacting NTM (non-tuberculosis mycobacterium)

In AIDS patients what would the induration be for a positive test?

5 mm induration

What is a newer more expensive test that can be used to diagnose latent TB?

Interferon gamma release assay (IGRA)

What does IGRA do? What are two benefits associated with it? What is a disadvantage?

It measures IGN-gamma release from white blood cells exposed to MTb. It is a lab based test so no followup is needed and no cross reactivity with BCG. However it requires skilled lab/infrastructure

How do we manage tuberculosis non-pharmaceutically?

1. Supportive care as applicable

2. Report to public health

3. If applicable report to IPAC

4. Routine practices for LTBI or extra pulmonary TB

5. Initiate airborne precautions for active pulmonary TB

What are the airborne precautions for active pulmonary TB?

1. Negative pressure room

2. Fit-tested N95 respirator

How do we treat LTBI with pharmaceuticals?

1. Isoniazid (INH) with vitamin B6 for 9 months

2. Rifampin for 4 months

Do other alternatives exist to treat tuberculosis if you have allergies or MDRO?

Yes