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