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2010-10-30 00:30:17

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  1. 10-27-c: Tuberculosis and other mycobacteria: Mycobacteria
    • “Fungus-bacteria”:
    • Waxy, hydrophobic cell wall: high lipid content (mycolic acid-long chain, branched; acyl lipids – short chain)
    • Unusual staining pattern:
    • Mycolic acid retains carbolfuschin, a phenolic red pigment, even after destaining with acid-alcohol:
    • So is “acid-fast bacillus” or AFB
  2. Mycobacteria: bacteriology:
    • Slender bacilli, beaded appearance
    • Non-spore forming, nonmotile, aerobic
    • Do not gram stain well:
    • Need to use Ziehl-Neelsen Acid Fast Stain!: know this name
    • Carbolfuchsin applied with heat
    • Decolorize with hydrochloric acid – ethanol
    • Counterstain with methylene blue
    • Kinyoun Stain:
    • Modified reagents, “cold”
    • Useful on tissue
  3. Mycobactera: bacteriology 2
    • Do not grow on routine lab media
    • Lowenstein-Jensen agar: egg, glycerol; malachite green (antibacterial)
    • Very slow growth: 12-18 hrs. generation time for most: 4-8 weeks for colonies to appear
    • Even the rapid growers are relatively slow: >/= 7 days for colonies
  4. Mycobacterium tuberculosis Colonies
    • “Buff, rough, and tough”
    • Produce niacin
  5. Dx of mycobacterium TB
    • Liquid media growth systems: Mycobacterial Growth Indicator Tube (MyGIT) – 4-14 days
    • Species identification: NAAT (rapid hours vs 6-12wks)
    • These have greatly shortened the turnaround time for TB diagnosis (or exclusion):
    • Check out p 1322 for mycobacterial species and how they fit together
  6. Mycobacterial Ecology
    • M. tuberculosis (MTB) id a human pathogen: M. bovis may also infect humans
    • M. leprae is a human pathogen
    • Nontuberculous mycobacteria (NTM): also called mycobacteria other than tuberculosis (MOTT) or “atypical” mycobacteria
    • Found in water and soil – cell wall structure is adapted
    • No human-human transmission:
  7. TB Pathogenesis
    • Respiratory droplets containing MTB are inhaled by a susceptible person:
    • Small droplet nuclei (1-5um) can reach the alveoli, where infection begins: most larger droplets deposit in the upper respiratory tract
    • MTB that reach the alveoli are ingested by alveolar macrophages:
    • Most are killed or inhibited
    • A small number multiply intracellularly and are released when the macrophages die
  8. If viable, these bacilli can spread through:
    • Lymphatic channels to regional lymph nodes
    • The bloodstream to other tissues and organs, including areas in which TB disease is most likely to develop:
    • Lungs
    • Kidneys
    • Brain
    • Bone
    • Liver
  9. Extracellular MTB attract bloodstream macrophages:
    • Most bacilli killed, granuloma forms
    • Specific T-cell immune responses develop:
    • MTB growth controlled, no progression
    • Generally develops 2-20 weeks after injection
    • At this point of TB infection, the tuberculin skin test (TST) will turn (+):
    • Asymptomatic and non-infectious
    • “Latent TB infection” – LTBI
  10. TB bacilli may overcome the immune system
    • Begin to multiply
    • Progression from TB infection to TB disease
    • May occur soon after, or many years after infection
  11. In the U.S., unless treated (people with positive PPD Tb test)
    • 7-10% of people will develop clinical Tb following infection
    • 5% within the first 1-2 years after infection
    • 5% later in life
  12. Increased risk of Reactivation
    • Recent TB infection (within the past 2 years)
    • Chest radiograph findings suggestive of previous tB
    • Immunosuppression: HIV infection, prolonged corticosteroids, other antilymphocyte Rx. (e.g. anti-rejection, anti-tumor), TNFalfa inhibitors
    • Substance abuse
    • Diabetes mellitus
    • Silicosis
    • Hematologic and lymphatic diseases
    • Head and Neck cancer
    • Stage 5 CKD (ESRD)
    • Gastrectomy, intestinal bypass, malabsorption
    • Low body weight, cachexia
  13. Immunity – less than stellar
    • Even with evidence of T cell response, ~10% of people develop active disease
    • Genetic testing of isolates has shown that people can get reinfected
    • Bacille Calmette-Gu’erin (BCG) Vaccine: may offer benefit in protection of disseminated disease in children, especially meningitis; range of efficacy from 0 to >90%
  14. TB Transmission
    • Droplet Nuclei:
    • Generated when coughing & singing; also when talking or sneezing
    • Can remain airborne for hours, even after an active case patient has left a room
    • # of MTB expelled in droplet nuclei is key:
    • Other factors:
    • Duration and intensity of exposure
    • Size and ventilation of “room”
    • Host factors
    • Closed spaces, recirculated air
  15. Case patients with AFB (+) sputum smears are more infectious than those with AFB (-) smears:
    • Among household contacts of smear (+) cases, rates of skin test (+) are 30-50% > than age-matched community controls
    • Among household contacts of smear (-) cases, rates of skin test (+) are only 5% > than age-matched community controls
  16. Higher risk for acquiring TB infection
    • Close contacts of person known or suspected to have active TB
    • Foreign-born persons immigrating from areas with high TB prevalence in last 5 yrs.:
    • Residents and employees of high-risk congregate settings (e.g. prisons, NHs)
    • **Health care workers (HCWs) who care for high-risk patients:
  17. Medically underserved, low-income, minority populations including IVDAs
    Infants and children exposed to high-risk adults
  18. General TB Epidemiology
    • Disease of antiquity
    • Germ Theory: Koch 1882 (Nobel Prize 1905); Pasteur 1864 – beer and wine, then milk
  19. Decline in TB incidence and mortality in the U.S. > 1900:
    • Improved socioeconomic conditions – more people living in single-family dwellings
    • Public health interventions:
    • Identifying active cases and infected people
    • Isolation of cases in sanatoria
    • ** Rx: (streptomycin 1946, isoniazid 1952)
    • Big change in the 1980s!!
  20. Unfunded public health TB programs:
    • HIV/AIDS epidemic
    • Immigration from countries where TB is highly prevalent
    • Transmission in congregate settings: jails, nursing homes
  21. TB back on decline in 1990s
    • Improved methods of identification:
    • More rapid and accurate better identification of resistant strains
    • Better identification of resistant strains
    • Improved follow-up by public health sector:
    • Increased federal resources
    • Decreased transmission in congregative settings, especially prisons:
    • Expanded use of treatment of latent TB:
    • Now most TB in U.S. is from foreign born people, up to 60%
  22. HIV and TB Epidemiology
    • People with TB infection who acquire HIV infection have a rate of TB reactivation of 7-10% per year vs <10% lifetime risk for a non-HIV infected person:
    • HIV (+) people who acquire TB infection progress to active TB at a rate of ~35% within 6 months vs 2-5% in 2 years for HIV (-)
    • High rates of extra pulmonary TB
    • Imperatives for testing
  23. TB Disease clinical features
    • “The consumption”:
    • Fever, weight loss/wasting
    • Night sweats
    • Malaise, anorexia
    • Cough >2wks; classically with bloody sputum
    • Chest pain, often pleuritic
    • Variable and may be more subtle!
    • Laboratory:
    • Nonspecific
    • Anemia (normochromic), hypoalbuminemia late
    • Late evidence of SIADH, adrenal insufficiency
  24. Extrapulmonary Disease
    • Hematogenous phase early in infection
    • “common sites”
    • CNS – acute or chronic meningitis, brain abscess
    • Kidney – one cause of “sterile” pyuria
    • Adrenal glands – Addison’s Disease
    • Liver – granulomatous hepatitis
    • Bone – spondylitis – classically described Pott’s Disease****!; long bones
    • Serosa – pleura, pericardium, peritoneum
    • Most often without active pulmonary disease:
  25. TB Disease Diagnosis
    • Index of suspicion!!!:
    • Growth of MTB is definitive
    • AFB (or fluorochrome) stained sputum smear is the most rapid method to detect presumptive MTB:
    • Sensitivity is only 50-70%
    • Half of people with active pulmonary TB may have (-) smears but (+) cultures
    • Sensitivity of AFB smears of “fluids” such as CSF, urine, etc. are <30#
  26. TB Diagnosis – caveats
    • (-) AFB smear does not exclude TB!!**: !
    • (+) Sputum AFB smear in a patient with suggestive illness has PPV of 90%
    • Yield of culture varies with AFB load: 3 specimens over 24-72 hrs
    • Growing role for NAAT: especially CSF and other “fluids”; direct test on sputum, best if AFB (+)
    • No role for skin testing in active disease!
  27. TB Rx
    • Population of MTB in patient with active TB:
    • Rapidly growing bacilli – usually in cavities
    • Slowly or intermittently growing bacilli – usually in the acid environment of necrosis
    • 2 phases of therapy:
    • initial rapid killing of large number of bacilli
    • longer phase during which bacilli with slower growth are killed – “sterilizing phase” or “continuation phase”
  28. TB Rx Early Activity
    • Rate of killing is fastest during the initial days of Rx with multiple agents
    • Measure is # of AFB observed on repeat sputum smear – decreased infectiousness
  29. TB Rx Sterilizing Activity:
    • Kill viable bacilli that are growing slowly or intermittently to minimize the risk of relapse
    • Measure is rate of positive sputum AFB cultures after 2 mo of Rx or relapse rate after Rx completed (<5%)
    • Better sterilizing activity = shorter regimen
  30. TB “First Line” Rx
    • Drug Abbreviation Early Activity Sterilizing activity
    • Isoniazid INH +++ +
    • Rifampin RIF + +++
    • Pyrazinamide PZA ++ +++
    • Ethambutol EMB ++ 0
    • Streptomcin SM + 0
  31. TB Rx – resistance
    • Development of resistance:
    • Patient non-compliance – argues for directly observed therapy (DOT)
    • Inappropriate prescription – wrong or too few drugs
    • Spontaneous mutation - ~1 in 10^5 – 10^8 bugs for any given drug
    • Resistance phenotypes:
    • Single drug, e.g. INH
    • Multiple drug resistance (MDR) – INH + RIF
    • Extensively drug resistant (XDR) – INH + RIF + fluoroquinolone + 2nd line injectable
  32. Isoniazid (INH)
    • Mechanism of action: inhibition of mycolic acid synthesis
    • Mechanism of Resistance: most likely enzyme inactivation; spontaneous mutation
    • Antimycobacterial Activity: bactericidal against intracellular and extracellular organisms; active as both an early agent and sterilizing agent
  33. Isonazid: Absorption, metabolism, excretion
    • Absorption: well-absorbed orally; wide distribution; CSF levels ~20% of serum levels
    • Metabolism: Metabolized in the liver by N-acetyl transferase
    • Rate of acetylation is genetically determined
    • Excretion: Drug (<10%) & metabolite excreted into urine
  34. Isoniazid Adverse reactions
    • Hepatitis:
    • Any time, peak in first 4-8 weeks
    • 15% develop elevated transaminases
    • risk increases with age, esp. >35 y.o.
    • Hepatic failure & death if drug is continued
    • Neurotoxicity: Increased excretion of pyridoxine so B6 is given with INH
    • Hypersensitivity reactions:
  35. Rifampin (RIF): mechanism of action, resistance, and antimycobacterial activity
    • Mechanism of action: .
    • Inhibits MTB DNA dependent RNA polymerase
    • Human enzyme insensitive to effects of the drug
  36. Mechanism of resistance: .
    • Presumably enzyme inactivation
    • Spontaneous mutation (1 in 10^6)
    • Antimycobacterial Activity: .
    • Bactericidal for all populations of MTB
    • Excellent nearly activity and sterilizing activity
    • Useful against intermittently metabolizing bacteria
  37. Rifampin: absorption, metabolism, excretion
    • Absorption: .
    • excellent oral absorption
    • Wide disribution, including CNS
    • Metabolism: .
    • Hepatic via cytochrome P-450 (deacylation)
    • Induces its own increased metabolism
    • Excretion: Mainly GI tract
  38. Rifampin Adverse Reactions
    • Hepatotoxicity: .
    • Cholestasis (increased ALP, increased bili)
    • Hypersensitivity reactions: .
    • Flu-like illness with intermittent use
    • Marked drug interactions: Induction of CYP-450 system
    • Brick red discoloration of body secretions: permanent discoloration of soft contacts
  39. Pyrazinamide (PZA): MoA, MoR, Antimycobacterial Activity
    • Mechanism of Action: Precise action unknown
    • Mechanism of Resistance: Unknown but evolves more rapidly than INH and rifampin when used alone
    • Antimycobacterial Activity:
    • Bactericidal at acid pH, especially on intracellular organisms
    • Good early & sterilizing activity
  40. Pyrazinamide: absorption, metabolism, excretion?
    • Absorption: .
    • Excellent oral absorption
    • Widespread distribution including CNS
    • Metabolism: Hepatic
    • Excretion: Renal
  41. Pyrazinamide Adverse Reactions
    • Hepatotoxicity
    • Gout
    • Photosensitivity
  42. Ethambutol (EMB): MoA, MoR, Antymycobacterial Activity
    • Mechanism of Action: an antimetabolite affecting RNA synthesis
    • Mechanism of Resistance: Unknown
    • Antimycobacterial activity: Bacteriostatic; ACTIVE EARLY, NO STERILIZING ACTIVITY
  43. Ethambutol: Absorption, metabolism, excretion
    • Absorption: excellent oral absorption; wide distribution including CNS
    • Metabolism: hepatic
    • Excretion: renal
  44. Ethambutol Adverse Reactions
    • Retrobulbar neuritis: (permanent) visual loss or color blindness; red-green color blindness, blurred vision
    • Peripheral Neuropathy:
    • Hyperuricemia:
    • Hypersensitivity reactions:
  45. Current TB Rx Scheme
    • Basic Principles: .
    • Multiple drugs – avoid resistance
    • Bactericidal
    • Long course
    • Start INH + RIF + PZA + EMB x 2 months
    • If bug INH & RIF susceptible: continue x 4 more months; discontinue PZA & EMB
  46. Current TB Rx Scheme Liver problems
    • Problem – liver dysfunction: Jaundice, elefated LFTs
    • Discontinue all Rx: .
    • Re-add one at a time and monitor for toxicity
  47. Identifying TB Infection
    • To eliminate TB fron the U.S. requires identification and treatment of those with latent TB infection and high risk for developing active TB:
    • High risk includes those persons:
    • Recently infected
    • With clinical conditions that increase the risk of developing active TB
    • Working in places where transmission of TB is more likely
    • Do not screen low risk persons or test for administrative purposes: .
  48. Targeted Tuberculin Testing
    Focuses tuberculin skin testing (TST) on high-risk groups rather than everyone
  49. Latent TB infection (LTBI)
    Person with a (+) TST with no evidence of active disease
  50. Treatment of LTBI
    Replaces the older terms “preventive therapy” and “chemoprophylaxis”
  51. Tuberculin Skin Testing
    • Sterilized broth from TB culture: .
    • PPD – purified protein derivative
    • 0.1 ml injected intradermally
    • Amount of induration @ 48-72 hrs:
    • Do not report results as “negative” or “positive”
    • Report results as mm of INDURATION
    • DO NOT measure amount of erythema
    • Tuberculin test, Mantoux test, TST & PPD, frequently are used interchangeably
  52. Interpretation of TST/PPD
    • Palpate induration
    • DO NOT measure erythema
    • Requires skilled individual to place and read
  53. Criteria for TST Positivity
    • Some soil NTM immunologically cross-react with MTB: Larger reaction more likely to represent MTB infection
    • Cut-offs for (+) TST range from 5-15 mm depending on TB risk
  54. No/low TB risk use ________ mm for TB
    >/= 15 mm
  55. >/= 10 mm TB used for
    • Recent immigrants (<5 yrs) from high prevalence country
    • IVDA
    • Residents/employees of high-risk congregate setting (e.g. prisons, hospitals)
    • Persons with certain clinical conditions: DM, cancer, silicosis, etc.
    • Children
  56. >/= 5 mm TB used for
    • PPD Reactor: (+) PPD of unknown duration; no prior test results not known
    • PPD Converter: Person with “negative” PPD reaction who on repeat testing has an increase in reaction size of >/= 10 mm within a 2-year period; high risk of developing active TB
  57. False Negative PPD
    • Anergy
    • Recent or overwhelming TB
    • Recent immunization with live virus vaccine(s)
    • Recent viral infection: measles; chickenpox
  58. PPD Alternative
    • Interferon Gamma Release Assay (IGRA): QuantiFERON Gold, Elispot
    • Measure response of peripheral blood mononuclear cells to specific MTB antigens:
    • Quantitative, no placement or reader error
    • Expensive but single visit
    • Not used in pregnancy
    • Particularly useful in people who have received BCG (no cross reaction):
    • Studies ongoing:
  59. BCG Vaccine & TST
    • PPD reactivity wanes over time after BCG vaccination
    • PPD testing can boost the immune response
    • Those with prior BCG vaccine should have a TST done if indicated
    • No reliable method to distinguish (+) reactions cause by BCG vs natural infection
    • HOWEVER, >/= 20 mm induration unusual with BCG
    • IFG Release Assay an alternative: will not be (+) in BCG recipients
  60. Treatment regimens for LTBI
    • INH 300 mg daily for 9 months preferred
    • INH 600 mg 2x/week – alternative
    • RIF 300 g daily for 4 months alternative: especially if evidence of resistance
  61. NTM/MOTT
    • Mycobacterium marinum: .
    • Fish tank or pond granuloma
    • Cutaneous lesions, typical history
    • Mycobacterium ulcerans: .
    • Buruli ulcer in the tropics
    • Severe skin ulceration, bone involvement
    • Mycobacterium kansasii: .
    • The most TB like of all the NTM/MOTT
    • BUT not transmitted person to person
    • Soil origin
  62. NTM/MOTT
    • Mycobacterium scrofulaceum: Scofula – lymphadenitis in children
    • Mycobacterium gordonae: generally a contaminant, “tap water bacillus”
    • Mycobacterium avium complex (MAC): severe disease in HIV
    • Mycobacterium Fortium complex: may cause local infection in normal or compromised host
  63. Leprosy
    • 4.2 million cases in the world: approx. 4200 cases in U.S. in LA and TX
    • 95% of population MAY be immune
    • Cardinal findings: infiltrative skin lesions; hypoesthesia; peripheral neuropathy
    • Tuberculoid – paucibacillary
    • Lepromatous – multibacillary