TB (3 questions) Flashcards
Cause of TB
Mycobacterium tuberculosis, an acid-fast bacilli that typically infects the lungs and respiratory track. It also infect brain, the kidneys, or the spine.
How does TB spread?
person to person via droplet nuclei containing tubercle bacilli through the air.
AIRBORNE precautions are needed in hospital setting
Who is at higher risk for exposure or infection with TB?
- Close contacts of people with infectious TB disease;
- people born in areas of the world where TB is common (foreign-born);
- low-income groups with poor access to health care;
- people who inject illegal drugs;
- infants, children, and adolescents exposed to adults in high-risk categories;
- & high-risk racial or ethnic minority populations, as locally defined.
- Also, people who live or work in certain settings such as nursing homes, correctional facilities, homeless shelters, and drug treatment centers and other people who may be exposed to TB on the job, such as health care workers.
Risk of developing TB disease if infected w/latent TB, if no risk factors
10% over a lifetime. 50% of those people will develop the infection within the 1st 2 years after exposure.
What groups are at higher risk for developing TB disease once infected?
- **people with HIV infection (strongest known risk factor for development of TB dz)
- people who were recently infected with M. tuberculosis,
- people with certain medical conditions (DM, silicosis, severe KD, organ transplant, immunosuppressive therapy, etc)
- people who inject illegal drugs (IVDU),
- and people with a history of inadequately treated TB.
For people infected w/ both TB and HIV, what is the risk of developing TB disease?
~ 7% - 10% each year
For people infected w/ both TB and diabetes, what is the risk of developing TB disease?
30% over lifetime
(~3x as high as those w/no risk factors)
How can we test for TB infection?
- TST/Manatoux Skin Test (PPD)
- nterferon-gamma release assays (IGRA) such as the QFT-G
How is TST test done?
- injecting tuberculin intradermally.
- After 48 - 72 hours, pt’s arm is examined for a rxn (an induration—firmness/swelling, NOT REDNESS).
Reasons for a false positive TST?
- infection w/ non-tuberculosis mycobacteria (NTM);
- Vaccination w BCG;
- administration of incorrect antigen,
- incorrect measuring/interpretation of TST rxn
Reasons for a false negative TST?
- Anergy // Recent TB infection (w/i. past 8-10 wks)
- Very young age (< 6 months)
- Recent live-virus measles or smallpox vaccination
- Incorrect method of giving the TST
- Incorrect measuring or interpretation of TST reaction
What is one strategy used to tell the difference between boosted reactions and those caused by recent infection?
Two step testing
TST: induration of > 5mm positive for what populations?
- living w/HIV
- recent contacts of persons w/infectious TB
- previously had TB disease
- organ transplants or other immunosuppressed pts (including prolonged course PO or IV corticosteroids or TNF-alpha antagonists)
TST: induration of > 10mm positive for what populations?
- moved to U.S. w/in 5 years from areas of world where TB common (e.g, Asia, Africa, Eastern Europe, Russia, Latin America)
- inject illegal drugs
- Mycobacteriology lab workers
- Live or work in high risk congregate settings
- medical conditions that put at risk for TB (silicosis, DM, severe KD, certain cancers, certain intestinal conditions)
- kids <4yo
- infants, kids, adolescents exposed to adults in high-risk categories
TST: induration of > 15mm positive for what populations?
people w/no known risk factors for TB
