Tuberculosis Lect 24 Micro Exam 2

Front 1

1) How is TB spread in the US?

Back 1

TB is almost always spread by inhalation of infected aerosolized secretions, such as may occur with coughing, sneezing or talking, from a person with infectious pulmonary tuberculosis.

Front 2

What are 2 major factors of spread of TB via the aerosol route?

Back 2

Two major factors favor spread of TB by the aerosol route: (1.) crowded living conditions; (2.) a population with little native resistance. Also, a third factor, virulance of the organism itself likely plays a role. Persons with active pulmonary TB and a sputum that is smear-positive for acid-fast bacilli (AFB) are highly contagious; however patients with negative sputum smears also can be infectious.

Front 3

What initiates primary TB infection?

Back 3

Inhalation of infectious, aerosolized droplets, usually from an unsuspected case of pulmonary TB and usually into the lower and/or middle segments of lungs, initiates primary TB infection.

Front 4

What are mycobacteria taken up by?
How does this spread to other phagocytes?

Back 4

Mycobacteria are taken up by alveolar macrophages, multiply within these cells, and then may spread within these phagocytes via lymphatics to regional lymph nodes and via the blood stream to distant foci such as kidneys and bone.

Front 5

Is this infection usually active or latent in people? What may happen at any time?

Back 5

In most TB-infected people (~90%) this infection remains latent for their lifetime; however, this containment may break down and the infection may "reactivate" at any time (~10%; highest risk is the first 2 yr following infection, but it may reactivate decades after the original infection) to produce active TB disease.

Front 6

What can be seeon on a chest xray in someone that has TB?

Back 6

“Ghon complex” (fibrotic, calcified lesions in the lung parenchyma and draining hilar nodes). In some cases (especially in exposed infants and young children, elderly, and immunosuppressed persons) the initial, primary infection may progress, either remaining localized in the lung or spreading systemically, to cause progressive primary tuberculosis.

Front 7

1) What immune system cell is needed to contain the infection?

Back 7

1) granulomas containing multinucleated giant cells.

-TB increased in those who can't make granulomas like impaired T cell immunity (AIDS, lymphoma). Those with lated TB and HIV + have 170X greater risk of getting active TB than those that are immunocompetent

Front 8

What is a BCG vaccination?

Back 8

In many countries, vaccination of infants and children with BCG, an attenuated, live strain of Mycobacterium bovis (a member of the M. tuberculosis complex), is provided routinely as protection against tuberculosis. While several studies have shown that BCG vaccination prevents severe, disseminated TB in infants and young children, its protection beyond that has never been demonstrated convincingly.

Front 9

What is the TST?

Back 9

Tuberculin skin test = get 5 units of purified protein derivative (PPD - mixture of proteins precipitated from a live TB culture) and injected intradermally.

Induration at site of injection reflecting local infltration of immune and inflmmatory cells is measure 48 to 72 hrs by health care professonal.

Front 10

Where can you see false positives with TST?

Back 10

usually due to cross reaction due to infection w/ non tuberculosis mycobacteria.
-common in immunosuppressed, elderly, people w/ viral infections

Front 11

Explain concept of Targeted testing
What are the highest risk categories?

Back 11

Tuberculin testing should be done today in the US only in persons at-risk for TB or those in whom TB would be a danger to the health of others. This is called Targeted Testing.
1. increased risk of exposure (e.g., close contacts of infectiousTB cases, health care workers).
2. increased risk of TB infection (e.g., foreign-born from area of high TB prevalence, homeless-depending on demographic).
3. increased risk of developing active tuberculosis if latent infection is present, because of impaired cell-mediated immunity (e.g., HIV, receiving immunosuppressive drugs such as corticosteroids, lymphoma).

Front 12

Describe the different sizes of TST induration. Based on these, who should be considered positive?

Back 12

1. >5mm. severely immunosuppressed (esp HIV+); close contact of infectious TB case; lesion on CXR consistent with old TB
2. >10mm from high incidence group; recent TST converted (documented change of at least 10 mm win 2 yer)
3. > 15 mm no known risk factors for TB

Front 13

What is QuantiFERON-Gold in Tube?

Back 13

Test that is based on rlease of interferon amma from sensitied T cells following in vitro stimulation with mycobacterial antigens.
Only measures those released by M. tuberculosis complex organisms.

Front 14

What does the T spot test do?

Back 14

This quantifies the number of interferon gamma producing T cells followin similar in vitro stimulation.

Front 15

What are some limitations of the QuantiFERON-Gold tube test and the T spot test?

Back 15

1. No good for sensitivity of tests for latent TB infection
2. need to prepare and stimulate blood cells within fixed time of drawing

Front 16

Where have QuantiFERON gold tube test and T spot test used in the past?

Back 16

often as surveillance using tests for TB infection. Especially for seeing in popluation of skin test conversions (change of at least 10 mm induration from a previous test administered within 2 year) - in specific settin - testing of employees working in hospital unit or homeless shelter.

Front 17

Describe the clinical symptoms of TB

Back 17

constitutional symptoms such as fevers, night sweats, weight loss, anorexia, and fatigue. However, in some cases these symptoms can be very mild or totally absent. Other symptoms will be localized to the involved organ system (e.g., cough in patients with pulmonary TB, back pain with vertebral TB, etc.). Patients also may deny symptoms because of fears and/or stigmatization.

Front 18

Describe pulmonary tuberculosis

Back 18

Primary TB ism ore common in kids, esp before age 5.
-effects lower or mid lung fields.
- Reactivation TB, also called “adult-type” tuberculosis, usually occurs in the lungs (80-85% of TB cases are pulmonary), and usually involves the apical or posterior segments of the upper lobe(s) or the superior segment of the lower lobe(s).

Cavities may be seen on chest X-ray, corresponding on pathology to areas of caseous necrosis containing large numbers of AFB.
-Pulmonary TB, along with TB of the larynx, can be the most infectious type of tuberculosis.

Front 19

What is extrapulmonary tuberculosis?

Back 19

Approximately 15-20% of new active TB cases in the US are extrapulmonary.

Almost any organ or system can be involved; outside the lungs, lymph nodes, especially cervical nodes, are the 2nd most common site (appr. 40% of extrapulmonary cases).

Tuberculosis may involve the larynx or tongue, where aerosolization may increase risk of infectiousness. Progressive involvement of multiple organ systems is referred to as miliary TB, since the lesions on cut section may grossly look like millet seeds.

Front 20

How is TB diagnosed?

Back 20

1. because culture of organism can take 2- 8 weeks, treatment for TB shouldn't be delayed if there's clinical suspicion is sufficiently high.

2. nucleic acid amplification test: rapid diagnosis (w/in hours).

Front 21

What are four first line antituberculosis drugs?

Back 21

isoniazid (INH), rifampin, pyrazinamid ethambutol

standard therapy: take these 4 for 8 weeks followed by 16 wk continuation phase w/ isonizid plus rifampin (6 mos).

Front 22

What is drug resistant TB?

Back 22

to cases of TB caused by an isolate resistant to at least one of the first line antituberculosis drugs. These patients may require a longer course of therapy and/or addition of other anti-TB drugs. Multidrug-resistant (MDR) TB is defined as resistance to at least INH and rifampin; appr. 1% of case-isolates in the US in 2007 were MDR, the most recent year for which drug susceptibility data are available.

Front 23

What is extensively drug resistant tb (XDR)?

Back 23

associated with extremely high mortality, is defined as MDR plus resistance to the fluoroquinolone class of drugs (e.g., Ciprofloxacin, Levofloxacin) and an injectable (kanamycin, amikacin, or capreomycin). The potential dangers of XDR are obvious, and serious efforts must be directed at its prevention.

Front 24

Who is responsible for the treatment of TB today?

Back 24

Public health system and provider, not the patient. Must be reported to health department.

Front 25

What are most cases of TB in the US a result from today?

Back 25

Most cases of tuberculosis in the US today result from reactivation of latent infection. Therefore, after assuring that persons with active TB disease complete an effective course of appropriate multi-drug therapy, our second public health priority is to prevent the occurance of disease- in persons who are infected.

Front 26

Why must pts w/ TB be treated with multiple drugs?

Back 26

Remember that although persons with Latent TB Infection (LTBI) may be treated with a single drug (this is done because the organism burden is lower in latent infection than the single-drug resistance mutation rate; see Dr. Brecher’s discussion), anybody with active TB MUST be treated with a multi-drug regimen because of the higher number of organisms present, in order to prevent the emergence of drug resistance.