Mycobacterium Tuberculosis Flashcards
Microbiology of Tuberculosis?
A.Aerobic, non-spore forming, non-motile bacillus
B.A mycolic acid cell wall
C.Slow generation time
D.Acid fast positive with Ziehl Neelsen stain
E.Fluoreses positive with auramine fluorochrome stain
F.Lacks pigment
G.Produces niacin and heat sensitive catalase
H.Reduces nitrates
I. Sensitive to INH
Mode of spread of tb? Risk of infection?
– Mode of Spread • Droplet nuclei of small size and high number (3000 per cough) • Prolonged exposure • Fomites not important
– Risk of infection • Infectiousness of source case (smear positive 50% conversion) • Closeness of contact
Risk of progression of infection to disease for TB? Influence of chemotherapy on infection spread?
– Risk of progression of infection to disease • Varies with age (under 3, young adults, elderly) • Varies with intensity of exposure • Increased risk in debilitated
– Influence of chemotherapy on spread of infection • Noninfectious after two weeks
Pathogenesis of PD prior to a positive PPD?
• Pathogenesis (prior to positive PPD)
– Droplet nuclei inhaled and deposited lower lobes of lung (airflow greatest)
– Unstimulated macrophages ingest organisms
– Infected macrophages to regional nodes (hilar, mediastinal)
– Lymph hematogenous dissemination • Extrapulmonary (CNS, kidney, bone, etc.) • Secondary pulmonary (apical posterior lung)
– Factors influencing fate of infection • Age of patient • Underlying immunocompromised states
Explain the immunopathology of TB?
–Small inoculi bypass mucocilia to alveoli
–Nonsensitized alveolar macrophages ingest organisms • Proliferate intracellularly
–T lymphocytes activated by macrophage antigen complex:
- Replication
- Production of lymphokines – Activate other T lymphocytes – Activate macrophages to produce lytic enzymes (cydal)
- Activated macrophages – Epithelioid cells – Langerhans giant cells (granuloma formation)
- Increase population of activated lymphocytes – Tissue hypersensitivity (positive PPD) 6-14 weeks after infection
What might the antigen load and tissue hypersensitivity tell you about whats going in the lung?
–Antigen load low – tissue hypersensitivity high - Granuloma
–Antigen load and tissue hypersensitivity high – Caseous necrosis
Ppl who are high risk for TB?
- Persons with HIV infection
- Close contacts of known infectious tuberculosis
- Persons with other medical risk factors which increase the risk of tuberculosis once infection has occurred
- Foreign-born persons from high prevalence countries
- Medically underserved low-income populations, including high-risk minorities (especially Blacks, Hispanics, and Native Americans)
- Alcoholics and intravenous drug users
- Residents of long-term care facilities, such as correctional institutions and nursing homes
TB is a systemic disease and it may affect what areas of the body?
• Lungs • Pleura • Central Nervous System • Lymphatic system • Genitourinary system • Bones and joints • Any other body organ or tissue
Groups to screen with a tuberculin skin test?
- Persons with HIV infection
- Close contacts of known infectious tuberculosis cases
- Persons with other medical risk factors which increase the risk of tuberculosis once infection has occurred
- Foreign-born persons from high prevalence countries (e.g., those from Asia, Africa, and Latin America)
- Medically underserved low-income populations, including high-risk minorities (especially Blacks, Hispanics, and Native Americans)
- Alcoholics and intravenous drug users
- Residents of long-term care facilities, such as correctional institutions and nursing homes
- Other populations which have been identified locally as having an increased prevalence of tuberculosis, e.g., health care workers in some areas
Medical risk factors that increase the risk of developing TB once the infection has been acquired?
- HIV infection
- Silicosis
- Abnormal chest radiograph showing fibrotic lesions
- Diabetes mellitus
- Prolonged corticosteroid therapy
- Immunosuppressive therapy
- Hematologic and reticuloendothelial diseases (e.g., leukemia and Hodgkin’s disease)
- End stage renal disease
- Intestinal bypass
- Post-gastrectomy
- Chronic malabsorption syndromes
- Carcinomas of the oropharynx and upper gastrointestinal tract
- Ten percent or more below ideal body weight
Explain a TB skin test?
- Use intradermal Mantoux test
- 0.1 ml of 5 TU PPD tuberculin
- Read 48-72 hours after application
- Needles should not be recapped, bent, broken, or removed from syringes
- Gloves are not necessary
Classification of TB skin test, reaction of 5mm is positive in?
A reaction of ≥ 5mm is positive in:
- Close contacts to patients with infectious tuberculosis
- Persons with HIV infection
- Persons who have chest radiographs with fibrotic lesions
In a TB skin test a 10mm lesion is positive in?
A reaction of ≥ 10mm is positive in:
- Persons with medical risk factors which increase the risk of tuberculosis once infection has occurred
- Foreign-born persons from high prevalence countries
- Low-income populations, including high-risk minorities
- Intravenous drug users
- Residents of long-term care facilities, such as correctional institutions and nursing homes
- Other high-risk populations indentified locally e.g., health care workers in some areas
A reaction of 15mm is positive in?
• Persons with no additional risk factors for tuberculosis
TB diagnosis? what is essential?
Examination for tuberculosis normally includes:
- History
- Physical examination
- Mantoux tuberculin skin test
- Chest radiograph
- Bacteriologic/histologic
- Examination for smear and culture
A positive bacteriologic culture for M. tuberculosis is essential to confirm the diagnosis of tuberculosis
How do we collect the specimen when we suspect TB?
Specimen collection: • Persons with suspected pulmonary or laryngeal tuberculosis should initially have at least three sputum specimens examined by smear and culture
• Additional methods to obtain sputum specimens: – Gastric aspiration – Sputum induction – Bronchoscopy
Lab examination for TB?
- Microscopic examination of stained smears for acid-fast bacilli (AFB) may provide first clue to diagnosis
- Culture examination confirms the diagnosis, may take 3 to 6 weeks
- Follow-up sputum examinations are critical for determining length of therapy and for documenting that the patient is non-infectious
Pulmonary disease stages for TB?
Primary infection
Chronic
Cavitary
Explain the primary infection of TB?
• Primary infection (Initial)
– Primary infection young adult
– Primary infection in adult years and old age
Explain chronic pulmonary TB?
Chronic Pulmonary TB
– Lower lobe disease
– Tuberculomas
- Begins as patch of pneumonitis apical posterior upper lobe – Mild disease – Atypical fibrous scar
- Extensive disease – Caseous necrosis – Reinfection of other lung segments – Cavitary disease – Rupture blood vessels with lymph hematogenous spread
Explain cavitary lesions in TB?
–Cavitary Disease
- Large amount of organisms
- Infectious state
- High incidence of disseminate – Reinfect other lung segments – Erode blood vessels with lymph hematogenous spread – Adjacent nonpulmonary edges (larynx, ears, GI tract)
- Other complications – Superinfection (aspergilli, atypical mycobacterium) – Underlying carcinoma
Treatment of TB general features?
- Tuberculosis should always be treated with at least two drugs
- After the initial phase of daily therapy, twice weekly therapy may be instituted
- Patient noncompliance is a major problem in tuberculosis control
- Patients must be monitored at least monthly for compliance and adverse drug reactions
American Thoracic Society Classification of Pulmonary TB?
American Thoracic Society Classification of Pulmonary TB
0 – No tuberculosis exposure (no exposure history, PPD neg)
I – Tuberculosis exposure, no evidence of infection (history of exposure, PPD neg)
II – Tuberculosis infection without disease (positive PPD, negative chest x-ray and microbiologic evaluation
III – Tuberculosis: infected with disease (positive PPD with xray and microbiologic evidence of active infection)
Explain the activity of isoniazid, Rifampin, Pyrazinamide, Streptomycin, and Ethambutol?
Isoniazid (INH) Bacteriocydal* against both intracellular and extracellular organisms
Rifampin (RMP) Bacteriocydal against both intracellular and extracellular organisms; maintains activity against very slowly metabolizing bacilli
Pyrazinamide (PZA) bacteriocydal only at acidic pH such as within cells; greatest activity in first few months of therapy
Streptomycin (STM) Excluded from the intracellular environment; active against only extracellular organisms
Ethambutol (EMB) Bacteriostatic* against both intracellular and extracellular organisms
*Bacteriocydal Killing the organism *Bacteriostatic Inhibiting growth of but not killing the organism
What are the two drug regiments for TB?
• The preferred 6 month treatment regimen includes: 2 months INH + RIF + PZA
4 months INH + RIF
• An acceptable alternative 9 month regimen includes: 9 months INH + RIF
INH toxicities? Follow up?
Toxicities: Hepatotoxicity, Neurologic (peripheral), hypersensitivity
Follow up with LFT’s and Pyridoxine.
Ethambutol toxicities and follow up?
Hypersensitivity and Optic neuritis
Follow up visual acuity.
Rifampin toxicities, Follow up?
Orange discoloration of secretions
Hepatitis
Reaction with other drugs (Warfarin, Quinidine)
LFT’s -follow up
Streptomycin toxicities, follow-up?
Renal toxicity, Vestibular damage.
Follow up: Creatinine.
