Staphylococcus aureus bacteremia

Methicillin sensitive staphylococcus aureus bacteremia (MSSA) is a life threatening condition. Even in the era of antimicrobial therapy, the overall mortality of approximately 30%. Once recognized, clinicians should focus on risk stratification and prevention of systemic complications. This is the reason for automatic infectious disease consultation following a positive blood culture with S. aureus.

Prior to speciation, gram stain results will become available and show gram positive cocci in clusters. This warrants the initial treatment with vancomycin, given methicillin resistant S. aureus (MRSA) is a possibility, which would not respond to traditional beta-lactam antibiotics. Risk factors for MRSA amongst patients with S. aureus bacteremia include previous colonization, nosocomial infection, older age, admission from long term care facility and history of broad spectrum antibiotics. Intravenous drug use has actually been found to be less associated with MRSA, though there have been conflicting results (JAMA Roghmann). 

Once identified as MSSA, patients should be switched from glycopeptide antibiotic (vancomycin) to beta-lactam (cloxacillin/ancef), given an identified mortality benefit in previous trials. The risk of complicated infection (systemic/metastatic infection - endocarditis, discitis, meningitis etc.), can be predicted using clinical and laboratory data. Fowler et al. found that community associated infections, fever at 72h post antibiotics, persistent blood culture positivity at 72h post antibiotics and skin changes suggestive of acute infections predict complicated bacteremia. This may lead to alterations in duration of antibiotic therapy, which is typically a minimum of two weeks. Predicting infectious endocarditis in these patients and need for echocardiography has been associated again with persistent bacteremia and presence of intracardiac devices.

See the link below to Fowler's article.

Predictors of complicated bacteremia