Mycobacterium tuberculosis: Disease (TB)
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Bacteria - Gram Indeterminate
- Mycobacterium tuberculosis: Overview
- Mycobacterium tuberculosis: Disease (TB)
- Mycobacterium avium
- Mycobacterium scrofulaceum
- Mycobacterium leprae
- Gardnerella vaginalis (Bacterial Vaginosis)
- Mycoplasma pneumoniae
- Tuberculosis: Disease
- Risk factors
- Immunocompromised patients
- Imprisonment
- Immigrants (TB-endemic regions)
- Healthcare workers
- General Symptoms
- weight loss
- night sweats, fever
- cough, hemoptysis
- Obvious due to pulmonary infection
- Primary tuberculosis
- Inhaled droplets with bacteria phagocytosed by alveolar macrophages
- TB replicates in alveolar macrophages
- Granulomatous focal lesion (Ghon focus) in lower lung
- Since inhaled droplets mainly end up in lower lung lobes
- Ghon complex describes a focus + lymph node
- Seen as focal lesion and hilar adenopathy on CXR
- Primary TB may be eliminated, but bacteria often survives in large caseating granulomas
- Inhaled droplets with bacteria phagocytosed by alveolar macrophages
- Latent tuberculosis
- Containment of bacteria in granulomas with healing and calcification
- asymptomatic, unremarkable CXR (hence “latent”)
- Positive tuberculin/PPD skin test due to past exposure
- Treat with INH
- Containment of bacteria in granulomas with healing and calcification
- Secondary (reactivated) tuberculosis
- Seen in immunocompromised individuals
- e.g. Advanced age, HIV/AIDS, steroid use, biologic drugs
- Failure of granulomas to contain bacterial spread
- Granulomatous cavitary lesions in upper lung
- Bacteria are predisposed to apex likely due to increased oxygen tension
- Liquefactive and caseating necrosis causes cavitation
- May disseminate (spread) into blood
- Miliary tuberculosis
- Widespread dissemination and seeding results in little focuses resembling millet seeds (hence, “miliary”)
- Potts disease (vertebrae)
- TB osteomyelitis caused by vertebral involvement
- TB meningitis
- Any organ may be involved
- Pericarditis, mediastinitis, skin lesions, and hepatic lesions also seen
- Miliary tuberculosis
- Seen in immunocompromised individuals
- Risk factors
- Diagnosis/Laboratory Tests for TB
- Real-time nucleic acid amplification (PCR)
- Rapid, first-line diagnostic study
- PPD (tuberculin) test for M. Tuberculosis (high yield)
- PPD stands for purified protein derivative
- Test for prior exposure + cell-mediated immunity (type 4 HSR)
- False negative result seen in immunocompromised patients
- False positive in BCG (Bacille Calmette-Guerin) vaccination
- Interpretation of positive results
- ≥ 15 mm in patients with no risk factors
- ≥ 10 mm in patients with risk factors (e.g., healthcare worker, traveling to endemic areas, and being in prison)
- ≥ 5 mm in immunocompromised patients (e.g., HIV, on immunosuppressants, and organ transplant recipients)
- Positive tests require a chest radiograph
- Interferon-gamma release assay (IGRA)
- Measure amount of IFN-gamma released by T-cells when exposed to TB antigens
- Test prior exposure and cell-mediated immunity
- Preferred over PPD b/c BCG-vaccinated people are negative
- Real-time nucleic acid amplification (PCR)
- Treatment
- RIPE is 1st line treatment for active pulmonary TB:
- Rifampin
- Isoniazid
- Administered alone for latent TB
- Pyrazinamide
- Ethambutol
- RIPE is 1st line treatment for active pulmonary TB: