Infectious Diseases | Microbiology / Positive Tuberculin Skin Test Flashcards
What infectious agent causes tuberculosis (TB)?
Mycobacterium tuberculosis
How is TB transmitted?
Person to person through droplet nuclei (in general, extended close contact is required for transmission)
In general, someone with untreated active TB will infect 10-15 people a year. True or false?
True
If a patient does not have drug-resistant tuberculosis and is compliant with appropriate treatment, about how long after the initiation of antibiotics does the patient become noninfectious?
2 weeks
What organs does TB affect?
Most often, the lungs; however, it can attack any part of the body
What are typical symptoms of active TB lung infection?
- Fatigue
- weight loss
- night sweats, fever
- coughing
- hemoptysis
- chest pain
What is latent TB?
Infection with M. tuberculosis without active disease
10% of the world’s population is infected with tuberculosis. True or false?
False (estimates are as high as 30%)
Even though patients with latent TB do not have symptoms, they are still contagious. True or false?
False. Latent TB is NOT contagious.
Why is it important to diagnose and treat latent TB?
- 5%-10% of people with latent TB can progress to active diseas
- active TB can be fatal
- Treatment of people with latent TB is an important step toward the elimination of TB in the community.
How often should healthcare and medical lab workers be tested for TB?
Annually
Who should be screened for latent TB?
- Healthcare and medical lab workers
- People who have contact with a person known (or suspected) to have active TB
- people with a compromised immune system (HIV infectionorgan transplant, etc)
- recent immigrants from areas where active TB is common
- people living in or who are exposed to people living in crowded conditions (homeless shelters, jails, etc)
- people with symptoms of active TB
- intravenous (IV) drug users
What is QuantiFERON-TB Gold?
- A highly specific whole blood test for TB that works by measuring a cell-mediated immune response in individuals infected with TB.
- It identifies both active and latent infection but cannot distinguish between the two.
What is the Mantoux tuberculin skin test (TST)?
- An intradermal injection that screens for TB infection by inducing a delayed hypersensitivity reaction.
- Note: a screening blood test also exists, but it is less readily available and not the preferred method of screening.
How is a TST administered?
Tuberculin purified protein derivative (PPD) is injected into the volar surface of the forearm.
How long after administration should a TST be read?
Between 48 and 72 hours
If a patient does not return within 72 hours after administration of a TST, what should be done to screen the patient for TB?
Reschedule another skin test as soon as possible (unless the patient had a severe reaction to the first test).
What constitutes a positive TST reading?
An area of induration (not just erythema) at the site of injection. For most patients, the area of induration must be at least 15 mm in diameter. For higher-risk patients (immune compromised patients, recent immigrants, drug users, etc), a smaller area of induration (ie, greater than 5 mm or 10 mm) indicates a positive result (specific tables are available from the CDC).
When should retesting occur for patients who have a known recent contact with a person with active TB but whose TST is negative?
12 weeks after contact (Note: in some cases, treatment for latent TB should start prior to the 12-week mark even if the TST is negative)
What is the BCG (bacille CalmetteGuérin) vaccine?
- A TB vaccine used in some countries where active TB is common.
- Persons with previous BCG vaccination may have a false-positive TST- however, this should not preclude screening.
What is the next step following a positive TST result?
Determine if the patient has active TB by taking a history, examining the patient, and obtaining a chest radiograph
What is the preferred drug regimen (per the CDC) for treatment of latent TB?
Isoniazid (INH) for 9 months
What is the most severe adverse effect of INH?
Hepatotoxicity
What baseline laboratory tests are necessary before the initiation of INH therapy?
For most patients, NO baseline laboratory tests are necessary.
- Liver function (AST, ALT, and bilirubin) should be tested at baseline and then monitored routinely in patients with a history of
- liver disease (or who use alcohol regularly)
- HIV infection, or
- pregnancy (up to 3 months postpartum).
What is the purpose of monthly clinical monitoring of patients on INH?
- To assess adherence to regimen
- inquire about symptoms of peripheral neuropathy and/or hepatitis, and examine for signs of hepatitis
What are some symptoms of hepatitis?
- Gastrointestinal upset (nausea and vomiting, abdominal pain), dark urine, jaundice
Patients on INH who are otherwise asymptomatic should discontinue INH if their transaminase levels reach what level?
Five times the upper limit of normal
Patients on INH who are symptomatic should discontinue INH if their transaminase levels reach what level?
Three times the upper limit of normal
Which medication can prevent INH-induced peripheral neuropathy?
Pyridoxine 25-50 mg PO once daily
