Infectious

Question 1

TB microbiology

Answer 1

a. Caused by Mycobacterium tuberculosis
b. Mycobacteria are acid-fast bacilli(AFB)_ considered slow growing but hardy organisms
c. Inhibited by the cellular arm of the immune system( high risk in HIV pt )

Question 2

Transmission of TB

Answer 2

a. Transmission occurs via inhalation of aerosolized droplets containing the active
organism
b. Only those people with active TB are contagious (e.g., by coughing, sneezing)
c. People with primary TB are not contagious

Question 3

Primary TB

Answer 3

• Bacilli are inhaled and deposited into the lung, then ingested by alveolar macrophages
• Surviving organisms multiply and disseminate via lymphatics and the blood-stream. Granulomas form and “wall off’ the mycobacteria. The granulomas in oxygen-rich areas, such as the lungs, allow these organisms to remain viable (they are aerobes). After the resolution of the primary infection, the organism remains dormant within the granuloma
• An insult to the immune system may activate the TB at any time
• Only 5% to 10% of individuals with primary TB will develop active disease in their lifetime

Question 4

Secondary TB ( reactivation )

Answer 4

• Occurs when the host’s immunity is weakened (e.g., HIV infection, malignanc immunosuppressants, substance abuse, poor nutrition)
• Usually manifests in the most oxygenated portions of the lungs–the apical/ posterior segments
• Produces clinical manifestations of TB

Question 5

Extrapulmonary TB

Answer 5

• Individuals with impaired immunity may not be able to contain the bacteria at either the primary or the secondary stage of the infection
• This may result in active disease throughout the body
• It is common in patients with HIV because their cellular immunity is impaired

Question 6

RF of TB

Answer 6

a. HIV-positive patients
b. Recent immigrants (within the past 5 years)
c. Prisoners
d. Healthcare workers
e. Close contacts of someone with TB f. Alcoholics
g. Diabetics
h. Glucocorticoid/immunosuppressant use
I. Hematologic malignancy
j. Injection drug users

Question 7

Clinical features of primary TB

Answer 7

1. Primary TB
   a. Usually asymptomat.
   b. Pleural effusion may develop
   c. If the immune response is incomplete, the pulmonary and constitutional symptoms of TB may develop. This is known as progressive primary TB

Question 8

Clinical features of Secondary (active) TB

Answer 8

a. Constitutional symptoms fever, night sweats, weight loss, and malaise are common
b. Cough progresses from dry cough to purulent sputum. Hemoptysis suggests
advanced TB
c. Apical rales may be present on examination

Question 9

Clinical features of Extrapulmonary TB

Answer 9

a. May involve any organ.
b. Miliary TB refers to hematogenous dissemination of the tubercle bacilli
• May be due to a reactivation of dormant, disseminated foci or a new infection
• Also common in patients with HIV
• May present with organomegaly, reticulonodular infiltrates on CXR, and choroi-dal tubercles in the eye

Question 10

Radiographic Findings in
Primary TB

Answer 10

• Ghon complex–calcified primary focus with an associated lymph node
• Ranke complex–when Ghon complex undergoes fibrosis and calcification

Question 11

Diagnosis of TB is challenging in HIV patients because:

Answer 11

• PPD skin test result is negative.
• Patients have “atypical”
CXR findings.
• Sputum smears are more likely to be negative.
• Granuloma formation may not be present in the late

Question 12

Diagnosis

Answer 12

CXR
Sputum ( acid fast bacilli)
Definitive diagnosis takes 4-8 w
PCR ** can detect specific DNA more rapidly**
PPD
It’s a screening test for who may have been exposed to TVB
Just for patients with risk factors
Takes 2-3 days
If patients has never had a PPD test before repeat it in 1-2 w if the first test is (-)
If PPD is positive CXR is needed to rule out active disease

Question 13

CXR finding of TB

Answer 13

Upper lobe infiltrates with cavitations

.Chon complex and Ranke complex: evidence of healed primary TB

Question 14

Why INH should always be started with vitamin B6 (pyridoxine)?

Answer 14

to prevent symptoms of B 6 deficiency which include :
stomatitis, glossitis, cheilosis convulsions, hyperirritability, peripheral neuropathy, and sideroblastic anemia.

Question 15

Rx of TB

Answer 15

isoniazid (INH), rifampin, pyrazines and ethambutol or streptomycin.
For 2 months followed by a 4-month phase of INH and rifampin.
2. Prophylactic treatment for latent :
9 months of INH after active TB has been excluded (negative CXR, sputum both).

Question 16

Imp notes for Rx TB

Answer 16

• For a positive TB exposure and a positive PPD test (but no active disease), treatment is INH only.
• If the patient has active
TB, multiagent therapy is indicated.

All TB medications can cause hepatotoxicity. Discontinue treatment only if liver transaminases rise to 3-5 times the upper limit of normal