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