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Which mode of transmission is primarily responsible for the spread of tuberculosis?
Which of the following groups is at the highest risk for developing active tuberculosis?
What is the importance of identifying the etiology of tuberculosis?
What is the primary cause of increased mortality rates due to tuberculosis since 2005?
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What differentiates latent tuberculosis infection from active pulmonary tuberculosis?
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Which of the following is NOT considered a risk factor for tuberculosis infection?
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What is the primary bacterial species responsible for tuberculosis?
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Which form of tuberculosis can occur outside of the lungs?
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What is a common laboratory test used to screen for tuberculosis?
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Which of the following is a public health strategy to monitor tuberculosis in populations?
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Which of the following is a primary method of tuberculosis transmission?
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What population has the highest risk for developing active TB disease?
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What pathological process occurs first after mycobacteria are inhaled into the lungs?
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Which of these conditions is not typically considered a risk factor for tuberculosis?
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What is a characteristic feature of primary tuberculosis?
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Which type of tuberculosis is characterized by cavitary lesions on X-ray?
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Which test is preferred for screening individuals who have previously received the BCG vaccine?
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What percentage of people with latent TB infection may reactivate?
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Which factor might cause false negatives in the Mantoux tuberculin skin test?
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What type of active TB occurs outside of the lungs?
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Study Notes
TB Risk Factors
- Individuals working in high-risk facilities: Hospitals, homeless shelters, correctional facilities, nursing homes, and HIV homes
- Persons with compromised immune systems:
- Babies and young children
- HIV infection
- Diabetes mellitus
- Severe kidney disease
- Chronic systemic corticosteroids
- Substance use disorder
- Silicosis
- Low body weight
- Organ transplants
- Head and neck cancer
- Immunosuppressive treatment for rheumatoid arthritis or Crohn’s disease
TB Pathophysiology
- Mycobacteria infected droplets are inhaled into the lungs
- The upper lobes are most commonly affected
- A healthy immune system can usually prevent TB from replicating (alveolar macrophages)
- The immune system is typically unable to fully destroy the bacteria
- Once a TB infection is established, lymphatic and hematogenous dissemination occurs before an effective immune response
- T-cells and macrophages form granulomas to encase the TB
- The caseating granulomas usually form in lung apices
Different Types of TB
- Primary TB: Typically asymptomatic and does not show up on X-rays, often occurs in children. If symptoms present, they include: cough, chest pain, night sweats, poor appetite, problems gaining weight.
- TB Disease (Active TB): Presents with symptoms and shows up on X-rays as a cavitary lesion. Symptoms include: fever, night sweats, weight loss, poor appetite, weakness, chest pain, sputum production (hemoptysis).
- TB Infection (Latent TB): Asymptomatic and not contagious, presents with a normal CXR and positive PPD or QuantiFERON test, there is a 5-15% chance of reactivation.
- Extrapulmonary TB (Active TB): This type of TB affects bones, kidneys, lymph nodes and the central nervous system, it can also be miliary or disseminated.
TB Etiology
- Mycobacteria Tuberculosis: acid-fast bacilli (AFB)
- Spread through the air via coughing, sneezing, or talking by an infected person
- Aerosolized mycobacteria can last in the air for several hours
TB Epidemiology
- M tuberculosis infects 2 billion people, approximately ¼ of the world’s population
- 10.6 million new cases of TB worldwide in 2021
- 1.6 million people died from TB in 2021, a 15% case fatality rate
- Increased in mortality for the first time since 2005
- Approximately 13 million people infected in the United States
- 7860 reported active cases in the United States in 2021
TB Risk Factors
- Individuals with recent TB infections
- Close contacts of someone with infectious TB disease
- Individuals who have immigrated from areas with high rates of TB (Latin America, the Caribbean, Africa, Asia, Eastern Europe, and Russia)
- Children under five years of age with a positive TB test
- Disproportionate rates in disadvantaged populations: people experiencing homelessness, malnourished individuals, substandard housing, and injection drug users.
- Individuals with other diagnoses, such as HIV infection
Screening Tests
- Used primarily to test for TB infection (latent TB)
- Positive test does NOT distinguish between infection and disease
- Utilized in:
- Those who have spent time with someone with TB disease
- People from countries where TB disease is common
- Individuals who live or work in high-risk settings (correctional facilities, nursing homes, homeless shelters)
- Healthcare workers caring for patients at risk for TB disease
- Infants, children, and adolescents exposed to adults at risk for latent tuberculosis infection of TB disease
Screening Tests: Options
- Mantoux tuberculin skin test (TST) (PPD test - Purified protein derivative)
- Sensitivity: 77%
- Specificity: 97%
- Only 59% specific with prior BCG vaccination
- Preferred for children less than 5 years old
- False negatives in immunosuppressed individuals
- IGRAs (interferon-gamma release assays) {QuantiFERON gold}
- Sensitivity: 60-90%
- Specificity: 95%
- Preferred for those who have received the BCG vaccine (Bacillus Calmette–Guérin - Mycobacterium bovis)
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