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101 Cards in this Set
- Front
- Back
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What causes TB?
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Mycobacterium tuberculosis
Rarely M. bovis, M. africanum and M. microti |
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Why was TB named like this?
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Describes the granuloma (tuber = potato growth)
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What is consumption?
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TB
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How is TB spread?
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Airborne droplet nuclei expelled by a TB carrier mostly with coughing
<5um |
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How many droplet nucleai spread by a cough?
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3000
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How long do droplet nuclei remain in air?
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Several hours
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How long are TB baccilli viable in environment?
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Longer than other bacteria due to waxy coat
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What factors determine the probability of transmission of TB?
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Infectiousness of index case
Environment of exposure DUration of exposure |
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What is an "open case" of TB?
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One who expells TB
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What does probability of infection with TB depend on?
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Extent of exposure
- high risk if close prolonged contact - low risk if sputum smear neg and extrapulmonary dz Susceptibility of infection |
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How many persons does an open case of tb infect each year?
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12-15
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Describe TB pathogenesis
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TB ingested in lung by macrophages
Bacilli multiply in macrophages Spread occurs via bloodsream Normally infection checked by immune system, DISEASE is prevented |
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Once infected, how long infected?
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Years, perhaps life
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What percent infected develop TB disease?
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10% in HIV neg (asx - only evidence is + PPD)
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Once infected, how often do HIV + progress to dz?
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Increase 10% per year
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What increases risk of infection progressing to dz?
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HIV
Substance abuse Recent infection CXR showing previous dz DM Silicosis Prolonged steroids Other immunosuppression Malnutrition Impaired cell mediated immunity |
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What is the natural outcome of dz, if not treated in 5 years?
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50% pulmonary tb die
25% self cure 25% ill with chronic infectious tb |
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What are the stages of TB dz?
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Primary infection "primary complex"
Latent TB infection (LTBI) Post primary TB (by reactivation or reinfection) |
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What is a Ghon focus
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An area in lung with locally lodged bacilli (normally R upper)
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What is a Ranke complex?
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Ghon focus (in r upper lung) and hilar lyphadenopathy"
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What is the "primary complex" of TB?
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Ranke complex (Ghon focus plus hilar lymphadenopathy)
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What happens after Ranke complex in TB?
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Apical scarring in some -- reidual bacteria calcified
Immune response in 4-6 weeks 10% pulmonary/pleural infection, disseminated dz; 90% no clinical dz/(+) PPD |
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What is post-primary TB?
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Months to years after latent period
TB reactivated Upper lobe infiltrates Extensive lung destruction (caseation) Cavity formation (+) sputum smear |
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Are most TB cases primary or post primary?
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Post primary
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When does post-primary TB most commonly occur?
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Adulthood
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WHen does primary TB most commonly occur?
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Childhood
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Describe a TB granuloma
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Central necrosis, surrounded by epithelial cells, angerhands giant cell, and lymphocytes on the outer edge
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What are the sx of post-primary TB?
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Cough > 3 weeks
Sputum Weight loss Fever, night sweats, fatigue, anorexia, chest pain, hemoptysis, breathlessness |
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Common sites of TB dz? (7)
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Lungs
Pleura CNS Lymphatic GU system Bones/joints Disseminated (miliary) |
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Is positive sputum smear necessary for TB+
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No
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Does HIV increase risk for TB infection?
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NO
But increases risk for dz |
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What is the role of immunity in TB dz process?
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Chronic antigenic stimulus causes macrophage activation, release of reactive metabolic intermediates/hydrolases
Loss of balance So, immune response creates some of the damage (granulomas, cavitations, caseation, fibrosis) |
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What are the most infectious TB lung lesions?
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Cavitations (as big pockets of TB infection communicating with outside world)
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Does AFB cording relate to virulence?
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Cords grown on culture
Used to thing yes, increased virulence Now know the answer is "No" |
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Is there possible genetic susceptibility to TB?
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Yes (africans twice as likely to become infected than Europeans)
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What is the Lubeck disaster?
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1926 Germany
BCG vaccine mixed up with virulent TB (!!) 251 children injected 31% died 50% xray confirmed dz 19% no evidence dz SHOWS INDIVIDUAL VARIABILITY OF PROGRESSION TO DZ |
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Describe mycobacterium tuberculosis microscopy?
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Straight/sl curved rods
Cannot gram stain Waxy lycolic acid/lipid cell wall prevent gram stain Acid fast stain needed |
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Are TB slow or fast growing in culture?
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Slow! 12-24 hour generation time (vs. 20 min in E coli)
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What does TB look like by AF stain?
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Thin bacilli, singly or in bundles "beaded appearance"
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How to acid fast stain:
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Expose specimen to hot carbol fuchsin dye...which penetrates the waxy coat.
Heat bound dye does not wash off with solvents. Wash with 3% acid alcohol Counterstain with blue or green dye |
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How to M. tuberculosis look on acid fast stain?
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Pink or a green/blue background
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How to Dx TB?
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PPD
CXR Sputum smear for AFB Culture for mycobacteria Rapid dx by DNA probes |
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What is LTBI?
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Presence of M Tuberculosis without sx or xray evidence of dz
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How to dx LTBI?
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PPD
IGRAs |
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What is the IGRA test?
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Interferon Gamma Release Assay
Measures IFN-y release by sensitized T cells stimulated with M. TB antigens Done via blood test |
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What is anergy
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No reaction to PPD
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How is a + PPD defined?
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> 15mm
>10mm in child >5mm in HIV + |
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Can cxr be nagative in pulmonary TB?
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Yes...hard to differentiate from LTBI
Normally have another sx (f/c, sweats, cough, wt loss, anorexia) or a positive sputum smear |
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Who to test for LTBI?
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Contacts with known TB case
Foreign born endemic areas Residents/employees high risk settings HCW serving high risk clients Medically underserved/poor High risk racial/ethnic populations Children exposed to high risk adults IV drug users Homeless Jail |
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Who are high-risk for TB dz once infected?
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HIV
Recent M. tb infection Immunocompromised IV drug users Hx inadequate treatment TB |
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PPD width cutoff?
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15mm - no risk
>10mm - immigrant, IVDU, children < 4, immunocompromised, exposed infants/children/adolescents; TB lab workers; emplyees/residents of congregate settings >5: HIV+, organ transplant, close TB contact, CXR with prior tb |
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How to dx TB in a lab with microscopy?
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AFB smear
auramine stained smear (fluorescent) Histopathology (stained bx of lesion) |
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How to dx TB by culture/sensitivity?
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Conventional: Lowenstein-Jensen media, x 6 weeks
New: BACTEC, MGIT |
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How to dx TB by molecular methods?
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PCR
DNA probe Molecular typing (for id'ing strains/track outbreaks) |
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Do you need to cx TB if smear is positive?
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Yes
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What is Lowenstein Jensen?
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The solid medium (LJ Medium) thats used to cx tb
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What is a true pathogen?
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If one organism found (like an M. tb), indicates dz
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Why is TB testing hard?
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Many samples low # AFB
Mycobacteria hard to distinguish from each other Antibody test not useful TB can infect almost any tissue Slow growing on cx (7-42 d) |
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How to treat TB?
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Isoniazid (INH) and Rifampicin (R) -- most powerful bacteriocidal
Pyrazinamide (kills some) Streptomyin (kills some, esp extracellular) Ethambutol (bacteriostatic) |
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What is normal TB treatment regimen?
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4 drug therapy (HRZE), drop E when ssceptibility comes back?
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What does a dosing regimen of 2H3R3Z3E3/4H3R3 mean?
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2 months of first group, followed by 4 months of second.
Each drug given 3x/week |
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What is MDR-TB
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Multidrug resistent TB
Always resistant to INH and Rifampin May have other resistances |
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What is XDR-TB
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Extensively drug resistant TB
Found first in South Africa MDR(HR) plus resistance to any FQ and to one injectable (amikacin, capromycin, kanamcin) |
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XDR rates in US?
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76% foreign born
12% black 41% asian |
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What is the white plague?
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TB outbreak in 17th/18th century europe
Nearly 100% infected 25% of all deaths caused y TB |
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What caused the black plague?
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Yersinia pestis
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How much of the world is infected with TB
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1/3
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What was the first WHO declared public health emergency?
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1993 - TB
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Why is TB still out of control?
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Inadequate control programs
Increased drug resistance Neglected by governments High rates population growth HIV epidemic |
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How many new TB cases each year?
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9 million
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How many people die each year from TB?
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1.6 million (4400 per day)
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What percentage of people with untreated TB die from the dz?
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50-70%
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Why is meant by TB inequity?
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98% of deaths in low to middle income nations
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What is the leading cause of death in HIV?
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TB
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How many people fail to get access to TB treatment each year?
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1.8 million
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Where is the highest incidence TB (2006)
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Africa 363/100,000/year
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Where was the highest prevalence of TB in 2006?
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India
China Africa (69%) |
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Why does HIV make TB worse?
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Reactivates latent TB
Rapid progression in infection due to lack of CMI |
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What is the lifetime risk of TB in HIV positive?
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10%
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Does HIV increase TB infectivity?
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Yes, high TB prevalence in HIV population leads to increase transmission to non HIV positive
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Why a spike of TB cases in the US in 1992?
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Decline in control programs
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Number of TB cases in US in 2008?
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12,904
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Mortality rate of TB is US?
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4.2
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Who are the biggest population of TB + in us?
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60% foreign born
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What caused the spike in TB cases by 20% in US between 1985 and 1992?
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HIV
Imigration of persons from high prevalence igh risk environ transmission (prisons, hospital, nursinghome, homeless shelters) Deterioration of TB public health infrastructure |
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What are concerns re: US TB?
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Limited DOT available
15 million persons infected -- 10% will turn positive Drug resistant TB growing |
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When did Do Not Board list begin?
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June 2007
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What country has the highest TB burden?
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India
505/100,000 2 million incidence |
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What is DOTS
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Directly Observed Therapy, Short course
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What are the 5 elements of DOTS? KNOW THIS
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Sustained political committment
Access to quality assured TB microscopy (NOT CX) Standardized short course chemo Uninterrupted supply of quality drugs Recording and reporting system enabling outcome assessment |
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What is the big problem with DOTS?
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Requires patients to seek treatment
Targets only active TB (not LTBI) |
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How does HIV impact DOTS?
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Rise in TB rates seen, despite DOTS
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How is DOTS different than other control programs?
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Control doesn't aim at uninfected population, but decreasing infectivity of infected
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WHO TB goals?
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2015: reduce prevalence by 50% relative to 1990
2050: Eliminate TB as a public health problem |
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WHO TB targets (know)
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Increase detection to 70%
Increase successful treatment to 85% |
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What is the problem of WHO detecting cases by smear postiives?
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Sputum smears + in only 44% of cases
17% of sputum smear negatives transmit infection |
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Problems with TB control?
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No new drug
HIV MDR and XDR No good field test No effective vaccine |
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What is BCG?
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Live attenuated vaccine from M. bovis
Reduced in lab till gene turned off Decreases TB meningitis Helpful in non-endemic areas (but not endemic areas) |
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Why do HIV positive patients have more drug resistance in TB?
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Malabsorption due to dz
Too many drugs/compliance prob Drug interactions? |
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When was BCG developed?
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Early 1990s
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Where is BCG recommended?
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WHO: All infants in countries with high TB rates
CDC: Pediatric pops where TB transmission high, Healthcare workers possibly exposed to resistant strains |
