Day #93 - Staphylococcus Aureus Bacteremia

Today we talked about a patient who presented with a febrile gastrointestinal illness who happened to have two diagnoses. First, a probable viral gastroenteritis acquired from his daycare aged son. Second, a concomitant staphylococcus aureus bacteremia.

I wanted to talk about the management of Staphylococcus Aureus Bacteremia. There is a good article here on the management of MRSA bacteremia.

• Never treat staphylococcus aureus in the blood as a contaminant. Like fungus in the blood, this always needs to be treated!
• The *minimum* treatment duration is 14 days (intravenous). This is for uncomplicated infections only.
  
  • Risk factors for complication:
    
    • Longer duration of illness
    • Community acquired infection
    • Persistent fever at 72h (OR 2)
      
    • Persistent positive blood culture at 96h (OR 5)
      
    • Hemodialysis patients
    • Indwelling lines or other prosthetic material
    • MRSA
    • No identifiable source for the bacteremia (i.e. no skin or line focus)
    • Blood cultures positive within 14 hours of drawing them
      
• You need to exclude bacterial endocarditis. Present in 10-13% of cases...
  
  • TEE is much more sensitive than TTE for making this diagnosis (103 patients with SA -- TEE dx endocarditis in 25%, TTE only found 7%). In patients for whom you are planning 14d therapy (particularly those who have risk factors for complication) you should probably not rely on a TTE to exclude IE.
• Can also cause pacemaker and AICD infections
• Vertebral osteomyelitis
• Septic arthritis
• Splenic abscess (persistant fever, LUQ pain)
  
• Septic thrombophlebitis (particularly with lines)
• Septic pulmonary emboli
  
• Brain abscess/meningitis/mycotic aneurysms
• Skin/soft tissue abscesses

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Treatment:

• Ideal treatment for MSSA is with a beta-lactam like cloxacillin or cefazolin. These are superior head to head with vancomycin for the treatment of MSSA.
• Removable foci should be removed if feasible and practical to do so
• Duration depends on complications. IE 4-6 weeks. Osteo ~6 weeks.
  

Risk of Death

• 20 to 40%!
• Age
  
• MRSA (OR 9.3)
• Blood cultures positive less than 12 hours (OR 7)
• Complication (OR 9)
  

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In medicine we often attempt to find one unifying diagnosis that explains all symptoms -- in satisfying what is known as Occam's Razor.

The important teaching point in a complicated case like this is that the patient may have multiple diagnoses and that we must keep an open mind. In response to Occam's Razor, Hickam's Dictum states that "[the patient] can have as many diseases as the damn well please".