10-26-c.txt

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10-26-c.txt
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10-26-c
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  1. STREPTOCOCCUS PNEUMONIAE – microbio, morphology
    • Gram (+)’ve in pairs and chains
    • Often lancet shaped diplococci
    • (Diplococcus pneumoniae)
    • Nonmotile, no spores
    • Important: Polysaccharide capsule which allows us to identify specific 90 types
    • Qwellung reaction with type specific antiserum
    • Has yielded to PCR
  2. Strep. pneumoniae
    • Best in CO2 containing atmosphere
    • Need catalas: blood or blood agar best; are ALPHA HEMOLYTIC (partial; green or viridans)
    • Autolytic system: shortly after reaching plateau growth; may impede recovery from clinical specimens
    • Optochin (quinidine derivitive) susceptible: Other viridans and streptococci are resistant
    • Bile soluble – activates autolysin
  3. Streptococcus pneumoniae - Virulence factors
    • Polysaccharide capsule
    • External to cell wall
    • Antiphagocytic
    • Antigenically diverse – it is the anticapsular Abs that protect against disease
    • Cell wall: fragments are pro-inflammatory
    • Cell wall polysaccharide: antigenically conserved and is the same from strep to strep
  4. Pneumolysin
    • Streptococcus pneumoniae-very important virulence factor
    • Cell membrane protein equivalent to a toxin
    • Blocking pneumolysin production attenuates virulence and prevents a lot of damage
  5. Colonization of pneumococcus in humans
    • Asymptomatic in 5-15% of healthy adults and 20-65% of healthy children
    • Spread requires prolonged and close contact
    • Rates of colonization and infection are seasonal: winter
  6. Streptococcus pneumoniae- Pathogenesis
    • Colonization of the nasopharynx: spread to sinuses or middle ear, microaspiration into lung
    • Once in lung: proliferation in alveoli, spread to other alveoli impaired gas exchange
    • Can move to lymphatics/ and/or get into blood stream, but NOT in all cases
    • Seeding of remote body sites if bacteremic: meninges, peritoneum, bone, joints – INFREQUENT
  7. PNEUMOCOCCAL INFECTIONS
    • Upper respiratory tract: sinusitis, acute or chronic / acute otitis media (“AOM”)
    • Lung:
    • Community-acquired pneumonia (CAP)
    • Healthcare associated pneumonia (HCAP)
    • May have associated empyema
    • May result in bacteremia
    • Remote infections following bacteremia: Meningitis, peritonitis, osteomyelitis, septic arthritis
  8. Predisposing conditions
    • Immunodeficiency syndromes: HIV, IgG (& subclass) deficiency
    • Splenic dysfunction/ splenectomy
    • Cirrhosis, alcoholism
    • Asthma, COPD
    • Smoking
    • Heart failure
    • Malignancy: Myeloma, chronic lymphocytic leukemia (CLL), lymphoma
  9. Pneumococcus pneumoniae – clinical frequency
    • Most common identified pathogen in adult Community-acquired pneumonia (CAP)
    • 20-60% depending on methodology and definitions
    • 30% of acute otitis media (“AOM”) with identified pathogens
    • Commonest cause of bacterial meningitis in U.S. especially for ages
    • 1-23 mos
    • >60 yrs
  10. Pneumonia – clinical features
    • Fever – release of cytokines: shaking chill
    • Cough – inflammation in the lungs: “rusty” sputum – a little bit of blood that make it into the alveoli in the course of the infection
    • Tachypnea – impaired gas exchange, cytokines:
    • Pleuritic chest pain:
    • May present atypically, esp in elderly: delirium, confusion
    • IMPORTANT: HYPERBILIRUBINEMIA may occur! Not necessarily biliary tree infection, might be a lung infection!
  11. Diagnosis – pneumonia
    • Sputum culture: must handle properly, negative in 50% of bacteremic cases
    • Blood cultures:
    • Urine pneumococcal antigen: Sensitivity 70-90% (higher if severe infection)/ Specificity 80-100% Useful even if Abx already started!
    • Pleural fluid culture
  12. CXR in pneumonia
    • “Lobar” – consolidative:
    • May “lag” with acute presentation:
    • May take weeks to completely clear:
    • Do not repeat early unless evidence of progression, Rx failure, etc.
    • Repeat 6-8 weeks after Rx in patients >40, especially if smokers – because may reappear and may be associated with an obstruction that don’t see right away
  13. Pneumococcal pneumonia – treatment
    • Penicillin – has been the drug of choice and highly susceptible until mid-1980’s
    • PCN resistance has steadily increased in U.S. and worldwide
    • Resistance increasing also to other antibiotics
    • Resistance mechanism – often from altered PCN binding proteins, sometimes due to transformation from other organisms
  14. Risk factors for penicillin resistant pneumonia
    • Recent antibiotic use most important
    • Very young (<1 year)
    • Day care attendees
    • Elderly
    • Nursing home residents
    • HIV infection
  15. Rx for pneumococcal pneumonia
    • PCN susceptible strains:
    • Penicillin
    • Cephalosporins
    • Fluoroquinolones
  16. PCN susceptible strains:
    • Penicillin (high doses)
    • Cephalosporins – often use first until know what it is.
    • Fluoroquinolones– often use first until know what it is.
    • Vancomycin
    • Linezolid
  17. Pneumonia prediction tools
    • PSI pneumonia Severity Index: Historical, physical, and lab data
    • CURB65: confusion, urea, RR, BP, age>65
    • Both discriminate between pts at high vs low risk of mortality, but are not absolutes, and good to use for deciding whether or not to hospitalize a patient
  18. Pneumococcal vaccines
    • 2 vaccines available in the U.S.
    • 23 valent polysaccharide (PPSV): safe, inexpensive, single dose, variable efficacy though, in the highest risk populations – the elderly (T-cell independent)
    • 7 or 3 valent conjugated (PCV) – conjugated that makes the immunity T-cell dependent – reduces nasopharyngeal carriage of vaccine serotypes in children – decreases transmission as well, and to adults, and the elderly

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