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12.12.05 Infection lecture

Infection sites
  • Osteomyelitis in old men
    • May well be from disseminated prostatitis
    • Not Strep/Staph like normal
  • Strep. milleri
    • Causes ABSCESSES
  • Easy-to-miss Staph. aureus
    • Osteomyelitis + endocarditis
    • Whereas skin/lines/soft tissue are obvious
  • Proteus
    • UTIs
  • Strep. bovis
    • Bowel malignancy (tumour allows invasion)
  • Bacteroides
    • Peritonitis (from gut flora)


Progression of endocarditis

  • Non-bacterial thrombotic endocarditis
    • vWF adheres
    • Platelets stick
    • Fibrin mesh
  • Invasion
    • => Vegetation
  • All starts with TURBULANCE, causing damage
    • Rheumatic heart disease
    • Congenital heart disease
    • Buggered valves
    • Hyperdynamic circulation?


Management of endocarditis

  • Cultures
    • Take 6, from multiple sites
    • c.f. Low levels, contaminants
  • Serology
    • If Pt has already had Abx
    • To check culture-negative Pt for low-level or weird pathogens
  • Echo
    • 65-95% sensitivity
      • Don't rely on echo for diagnosis
    • Very hard to see prosthetic valve endocarditis on echo
      • Tends to affect the ring of scar tissue, not the valve itself
  • Treatment
    • 3-6 weeks of penicillin + gentamicin
    • Surgery (esp. for prosthetic valve infection)
  • Abx for dental work??


Viridans Streptococcus

  • Most abundant in the mouth
  • S. mutans, is the etiologic agent of dental caries
  • Others may be involved in other mouth or gingival infections
  • Most common causes of subacute bacterial endocarditis
    • Have the unique ability to synthesize dextrans from glucose, which allows them to adhere to fibrin-platelet aggregates at damaged heart valves


Host factors for post-operative infection
  • Diabetes
  • Obese
  • Malnutrition
  • Smoker
  • Low albumin
    • Affects both healing and immune function
  • Prior irradiation
  • Prolonged pre-op stay
  • Steroids
  • S. aureus carriers
  • Old and poor ?


Skin infections

  • Impetigo
    • Dermis only
    • => Topical fusidic acid
  • Erysipides
    • Skin plus subcutaneous lymphatics
    • Raised edge, oedema
    • Typically GAS
  • Cellulitis
    • Skin and subcutaneous tissue
    • GAS or S. aureus
    • Be sure to exclude DVT
    • => High-dose pen + fluclox. + elevation


Necrotising fasciitis

  • Organisms
    • GAS (beta-haemolytic => aggressive spread)
    • Faecal organisms
  • Spreads along fascial planes => Systemic sepsis
  • High mortality
  • Treatment
    • Antibiotics including anti-ribosomal agents to block toxin production (not just bacteriostatic agents)
    • IVIG

Gas gangrene
  • Typically from anaerobes
    • e.g. Clostridium, from soil (WW 1)
  • Now mostly seen in IVDUs


Bacterial taxonomy



Notes
  • Blood cultures can be falsely +ve in laukaemia due to CO2 production from WBCs
  • Most common cause of splinter haemorrhages is trauma
    • e.g. Builders
  • Osler nodes are sore
  • Inflammation is a normal part of wound healing!
    • Don't be scared of a bit of redness
  • Clenched-fist injury is the same as a bite
    • Assume they're all infected
  • Paronychia = Skin infection that occurs around the nails
  • Skin cannot be sterilised
  • Puncture wounds look the best but fare the worst
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