Flashcards in 32 Tuberculosis Cupo Deck (30):
What is Mycobacterium tuberculosis (MTB)?
Long, thin rods that grow in masses or strands. Composed of complex layer of mycolic acid and waxes. Ziehl-Neelsen acid-fast staining procedure. Obligate AEROBES, non-spore forming, nonmotile. Requires enriched media for growth. Slow growing, multiplying in ever 12-24 hrs. Humans are the only reservoir for infection
What is the transmission of M. tuberculosis like?
Spread by droplet nuclei (< 25 micro-meters in diameter, midlung zones). Expelled when person with infectious TB coughs, sneezes, speaks. Close contacts at higher risk of becoming infected. Transmission occurs from person with infectious TB disease (not latent TB infection)
What are the symptoms of Primary TB?
Fever (not very common). Positive skin test after 4-8 weeks. Chest radiograph: lower zone disease, hilar enlargement (neither are common))
What are the symptoms of Reactivation TB (Pulmonary)?
Common: Cough. Less common: fatigue/malaise, weight loss, night sweats, fever. Tuberculin skin test positive in 85% of patients. Common: Upper zone disease, cavitation
What are some predisposing conditions for TB?
HIV infection and DM (anything with suppressed immunity, these two most common). Silicosis. Prolonged corticosteroid therapy. Other immunosuppressive therapy. Renal insufficiency. Post gastrectomy. Malignant lung or other tumors. Alcoholism. Massive weight loss
What is some general information on Latent TB Infection (LTBI)?
1/3 of the global population are infected w/ M. tuberculosis. ~10% progression to active disease. Progression to active disease greatest in first two years after transmission
What are the characteristics of LTBI?
Inactive TB infection. Patient often doesn't feel sick. NON-INFECTIOUS. Needs treatment for LTBI to prevent active TB disease. Radiographical studies negative for active disease. Positive TST (skin test) or QST (quantitative skin test)
What are the characteristics of Active TB?
Active TB bacteria infection. Patient feels sick and experiences coughing, fever, and weight loss. Highly infectious. Needs treatment to cure active TB disease. Radiographical studies may be abnormal. TST or QST usually positive. Respiratory specimens may be smear or culture positive
Who are people at higher risk for exposure or infection with TB that should be tested for LTBI?
Close contacts of a person known or suspected to have TB, Foreign-born persons from areas where TB is common, Residents and employees of high risk congregate settings, Health care workers who serve high risk clients, Person who inject illicit drugs
Who are people at higher risk for TB disease once infected that should be tested for LTBI?
Person with HIV infection. Person recently infected with M. tuberculosis. Person with certain medical conditions. Person who injects illicit drugs. Person with a history of inadequately treated TB
What is used for the diagnosis of Latent TB?
Mantoux skin test (PPD). Chest X-Ray. Whole-blood interferon-gamma assay
What is used for the diagnosis of Active TB?
Sputum smear (AFB). Plates/tubes. Bactec system. Difco system. Gene probes (Nucleic acid amplification)
What is the Smear Examination?
Results should be available within 24 hours of specimen collection. Presumptive diagnosis of TB. Increased sensitivity: Light vs. fluorescence microscopy, AFB x3, Induced sputum
What are the characteristics of "Cultures"?
"Gold Standard". Used to confirm diagnosis of TB. Culture all specimen even if smears are negative. Time to detection depends on the media (anywhere from 13-27 days). Liquid culture systems can detect small amounts of bacterial growth either using radioactivity or by oxygen concentration changes (can also be used for drug susceptibility testing)
What are the characteristics of Drug Susceptibility Testing?
Drug susceptibility testing on initial M. tuberculosis isolate (repeat for patients who do not respond to therapy). Have positive cultures despite 2 months of therapy. Promptly forward results to the health department
What are the characteristics of Chest X-Ray?
Cannot confirm diagnosis of TB. Abnormalities often seen in apical or posterior segments of upper lobe or superior segments of lower lobe. High resolution chest computed tomography (CT) is more sensitive than chest X-Ray
What is the administrating and reading of tuberculin skin test (PPD) like?
Inject intradermally 0.1 ml of 5 TU PPD tuberculin - concentrated filtrate from cultures of M. tuberculosis that have been heat killed. Produce wheal 6-10mm in diameter. Read reaction 48-72 hrs after injection. Measure only INDURATION (not red skin around it)
How is a positive PPD Test evaluated?
Positive if > 5mm in: HIV-infected persons, close contacts of infected person, person w/ abnormal radiograph, immunosuppressed. Positive if > 10mm in: Foreign-born person (< 4 yo. Positive if > 15 mm in: all others
What are some causes of False-Negative Tuberculin Tests?
Older age. Lower serum protein. Concomitant illnesses. Inactive tuberculin solutions. SQ vs. Intradermal. Corticosteroids. Booster testing
What is Quantiferon (QFT)?
TB Gold Test. T-lymphocytes release interferon-gamma in response to tuberculin antigen
What are the advantages of QFT?
Single patient visit to draw blood. Results available in 24hr. No booster effect. Not affected by prior BCG. Not subject to reader bias
What are the disadvantages of QFT?
Blood sample must be processed while WBCs are still viable. Limited data on use in children, in persons recently exposed to M. tuberculosis, and in immunocompromised persons. Errors in collecting sample. Limited data on use of QFT-G to determine who is at risk for developing TB disease
What are the Nucleic Acid Amplification Methods (NAAT)?
Performed on sputum or bronchoalveolar lavage (BAL) fluid. Results available within 1 day. NAAT amplification targets are not standardized therefore variable results. If sputum smear is negative, the specificity of NAAT has been 97-98%. False positive results are seen in patients w/ past medical history of TB and in patients with bronchogenic carcinoma
What is the treatment of LTBI like?
Treatment for LTBI should be administered only: After culture results (-), Active TB is no longer suspected. Chemoprophylaxis. Prevent or decrease risk of developing active TB
What are the treatment regimens for LTBI?
INH x9 months (QD/twice weekly). INH x6 months (QD/twice weekly) - daily regimen should not be used in HIV positive patients, those with fibrotic lesions on CXR, or children. RIF x4 months (daily)
What are the different CDPH Classifications for TB?
Class TB-0 (no TB exposure). Class TB-1 (TB exposure). Class TB-2 (latent TB infection, no disease). Class TB-3 (TB, clinically active). Class TB-4 (TB, not clinically active). Class TB-5 (TB suspect)
What is teh Bacille Calmette-Guerin (BCG) Vaccine?
Tuberculosis vaccine. Used in many countries with a high prevalence of TB to prevent childhood tuberculosis meningitis and miliary disease. Not used in the US. Epidemiologic evidence suggests that BCG immunization doesn't protect against the development of infection w/ MTB upon exposure
What is testing for TB like in BCG-Vaccinated Persons?
May cause (+) reaction to the tuberculin skin test (TST): may complicate decisions about prescribing treatment
For infection control in health-care setting, when should patients be considered infectious?
If they are: Coughing, Undergoing cough-induced or aerosol-generating procedures, Have sputum smears positive for acid-fast bacilli and they are not receiving therapy, have just started therapy, or have poor clinical response to therapy