11. Tuberculosis Flashcards
Clinical characteristics (type, transmission, incubation, symptoms)
Respiratory disease.
Majority of TB cases caused by M. tb
Transmission: M. tb spread via small airborne particles called droplet nuclei.
incubation: 2-12 weeks
symptoms: prolonged cough, coughing up blood, chest pain, fatigue
Pathogenesis for Latent TB and TB
Latent: Within 2 to 8 weeks, macrophages ingest and surround the Mycobacterium. The cells form a barrier shell, called a granuloma, that keeps the bacilli contained and under control.
TB: If the immune system cannot keep the tubercle bacilli under control, the bacilli begin to multiply rapidly (TB disease). This process usually occurs in the lungs, but can occur in different areas in the body, such as the kidneys, brain, or bone.
Latent TB clinical features
Are not infectious.
2-8 weeks after infection, can be detected by TST
TB disease clinical
In some, the granulomas break down, bacilli escape and multiply, resulting in TB disease
Can occur soon after infection, or years later
Persons with TB disease are usually infectious and can spread bacteria to others
TB vs Latent TB
Environmental Factors that Enhance Risk of Transmission
TB can live in the air for .appox. 4 hours.
High concentration of droplet nuclei in the air
Exposure in small, enclosed spaces
Poor ventilation that inadequately dilutes or removes droplet nuclei
Recirculation of air containing droplets
In hospital setting: positive air pressure in patient’s room causing flow to other areas
pop at high risk
Close contacts of person known or suspected to have active TB
Foreign-born persons from areas where TB is common
Persons who visit TB-prevalent countries
Residents and employees of high-risk congregate settings
Health care workers (HCWs) who serve high-risk clients
Populations that have increased incidence of latent M. tuberculosis infection or TB disease
Methods for Detecting M. tb Infection in U.S.
Individuals who should be tested for infection:
- Uninfected persons at high risk for LTBI
- Persons at high risk for progression to TB disease
2 testing methodologies
- Mantoux tuberculin skin test (TST)
- Interferon Gamma Release Assays (IGRA)s
Persons with positive TST or IGRA should be evaluated for TB disease
If disease is ruled out, consider LTBI treatment
If patient not willing or able to take treatment, educate on TB signs and symptoms
Reading the TST
Trained health care worker assesses reaction 48–72 hours after injection
Measure diameter of induration across forearm; only measure induration, not redness
≥5 mm induration is classified as positive in:
- HIV-infected persons
- Recent contacts of infectious TB
- Persons with changes on chest radiograph consistent with prior TB
≥10 mm induration is classified as positive in
- Recent arrivals from high-prevalence countries
- Injection drug users
- Residents and employees of high-risk congregate settings
- Mycobacteriology laboratory personnel
- Persons with conditions that increase risk for progressing to TB
- Children <5 years of age, or children and youth exposed to adults at high risk
≥15 mm is classified as positive
- Persons with no known risk factors for TB
Interferon Gamma Release Assays (IGRAs)
IGRAs detect M. tb infection by measuring immune response in blood
May be used for surveillance/screening
Preferred when testing persons
- Who might not return for TST reading
- Who have received Bacillus Calmette-Guerin (BCG) vaccination
BCG Vaccination
Vaccine made from live, attenuated (weakened) strain of M. bovis
BCG NOT generally recommended in the U.S
Testing for TB Disease
CXR- Chest abnormalities suggest, but do not confirm, TB disease. (as other diseases may show the similarity, further validation in skin/blood test)
Microscopy smears - Detect acidfast bacilli (AFB) in smears
All persons suspected of TB disease require a sputum culture (confirms diagnosis) Culture is the gold standard for diagnosis TB
Drug-Resistant TB
Caused by organisms resistant to one or more TB drugs
Transmitted the same way as drug-susceptible TB, and no more infectious (just harder to treat)
Treatment for Latent TB Infection
Treatment of LTBI essential to controlling and eliminating TB disease
Reduces risk of LTBI to TB disease progression
Several treatment regimens available utilizing 3 main drugs - isoniazid (INH), rifapentine (RPT) & rifampin (RIF)
Treatment for TB Disease
Goals: cure patient, minimize risk of death/disability, prevent transmission to others
Numerous drugs FDA approved for the treatment of TB disease, with multiple regimens available lasting 6 – 9 months
Ensure adherence and completion of therapy (Directly Observed Therapy (DOT))
