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Transthoracic Echo in Low-Risk S. aureus Bacteremia
Study Questions:
Can transthoracic echocardiography (TTE) help exclude infective endocarditis (IE) among low-risk patients with Staphylococcus aureus bacteremia?
Methods:
A retrospective cohort study of 833 consecutive hospitalized patients with S. aureus bacteremia from seven academic and community hospitals in Toronto, Canada, was conducted over a 3-year period (2007-2010). Patients who underwent TTE within 28 days of bacteremia (n = 536) were randomly divided into derivation and validation cohorts. Multivariable logistic regression analysis was used to determine high-risk criteria for IE in the derivation cohort, and criteria then were applied to the validation cohort to determine diagnostic properties. A high-risk cardiac condition was defined as any of: prosthetic heart valve or prosthetic material used for cardiac valve repair, congenital heart disease, cardiac transplantation with valvulopathy, history of prior endocarditis, or presence of a pacemaker or automatic implantable cardioverter-defibrillator.
Results:
Four high-risk criteria predicted IE: indeterminate or positive TTE (p < 0.001), community-acquired bacteremia (p = 0.03), intravenous drug use (p < 0.001), and high-risk cardiac condition (p < 0.004). In the validation cohort, the presence of any one of the high-risk criteria had 97% sensitivity (95% confidence interval [CI], 87%-100%) and 99% negative predictive value (95% CI, 96%-100%) for IE. The negative likelihood ratio was 0.05 (95% CI, 0.007-0.35).
Conclusions:
A normal TTE fairly reliably excluded IE in patients without any of the following: S. aureus bacteremia that was community-acquired, an underlying high-risk cardiac condition, or intravenous drug use. The authors concluded that this study provides evidence that clinical risk stratification combined with a normal TTE may be adequate to rule out IE in most patients with S. aureus bacteremia.
Perspective:
Among hospitalized patients with bacteremia, transesophageal echocardiography (TEE) frequently is ordered to ‘rule out’ IE, owing to its higher image resolution (and increased sensitivity in the detection of vegetations) compared to TTE. This important study suggests that low-risk patients can be identified in whom a normal TTE can reliably exclude a diagnosis of IE; reducing costs, and decreasing patient exposure to the risks of sedation and semi-invasive testing associated with TEE.
Keywords: Bacteremia, Defibrillators, Implantable, Diagnostic Imaging, Echocardiography, Transesophageal, Endocarditis, Endocarditis, Bacterial, Heart Transplantation, Heart Valve Diseases, Staphylococcus aureus, Staphylococcal Infections
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