Staph aureus bacteremia

Today we discussed staph aureus bacteremia. This is an important and serious internal medicine problem, and needs to be recognized promptly and treated effectively to prevent poor outcomes.

A few points:

-Colonization is either nasal or skin; of pts with SAB, 80% have exact same organism colonizing nose, but only ~1% of colonized people get SAB in 5 years.

-Remember that initially, you will not know whether it's staph aureus causing the gram +ve cocci on the gram stain. GPC in clusters may be any of St. aureus (MRSA or MSSA), St. epidermidis, E. faecalis. Safest to assume it's the worst and start vanco empirically e.g. 1g IV x 1 then reassess (unless very likely to be contaminant)

Major questions:
1) Is this endocarditis?
2) Is this "complicated"?
Uncomplicated SAB = removable focus (e.g. line, abscess). Complicated implies bone, joint or valve focus.

Predictors of complicated SAB:
1) community acquired
2) failure to defervesce at 72h
3) +ve BC at 72h on treatment
4) skin lesions

MSSA responds better to cephalosporins than vancomycin, so switch as soon as you know sensitivities.

Duration of therapy:
If no foreign bodies, catheters, valvular abnormalities, 14d IV minimum
If deep focus/endocarditis/peristent bacteremia despite treatment, 4-6 wks IV minimum

Most common "metastatic" sites of St. aureus:
1) Bone and joint
2) Kidney
3) Endocarditis
4) Spleen
5) Lung

Final pearl: If you see St. aureus in a urine culture, it probably came from the blood (never a contaminant), so take seriously!

Some links:

Click here for an epidemiological study on the outcomes of MRSA and MSSA bacteremias
Click here for a study on risk factors for persistent staph aureus bacteremia