1. In patients lacking any of the four high-risk criteria for Staphylococcus aureus infective endocarditis, including an indeterminate or positive TTE, community-acquired bacteremia, IV drug use, or a high-risk cardiac condition, a negative transthoracic echocardiogram effectively ruled out endocarditis.
Evidence Rating Level: 2 (Good)
Study Rundown: Staphylococcus aureus bacteremia (SAB) is associated with substantial community-acquired as well as healthcare-associated morbidity and mortality, and infective endocarditis (IE) is a severe complication. While urgent echocardiography has been shown to be a rapid and noninvasive tool for IE diagnosis and may facilitate timely management of infection-associated complications, clinical information guiding its application in risk stratification remains limited. The goal of this study was to develop a prediction model incorporating transthoracic echocardiographic (TTE) findings to assess IE risk in patients with low-risk SAB and study the potential of TTE imaging in SAB management. The authors designed risk stratification and diagnostic criteria based on a large cohort of patients who were treated for SAB, and then applied this derived risk-stratified diagnostic criteria to a validation cohort. Results showed that among low-risk patients, defined as those without community-acquired infection, complicated heart conditions, and intravenous drug use, IE can be effectively ruled out with TTE result is negative for SAB, with a negative predictive value of 99%. The risk of infective endocarditis was increased 14-fold with active IV drug use, 9-fold with a high-risk structural cardiac abnormality, and 3-fold with community acquired bacteremia, constituting a set of high-risk conditions in which TTE is not sufficient to rule out endocarditis. These findings are important for cost-effective management of SAB-associated IE and optimization of patient outcomes using intelligent risk assessment guidelines, as excessive imaging could be avoided in patients unlikely to develop IE. This study was limited due to variability in the clinical presentation of IE which may have led to exclusion of a subset of participants from the study who lacked the more definitive diagnostic features of IE. Additionally, conclusions generated from prospective studies, as opposed to this retrospective study, would have provided better support for the use of this risk-stratification tool, and should be a goal for future validating trials.
In-Depth [retrospective cohort]: A total of 536 out of 833 consecutive patients who underwent TTE within 28 days of SAB were assigned randomly to a derivation and validation group for this study. Participants were drawn from 7 health centers in the Toronto, Canada area enrolled in the study between 2007 and 2010. Subjects were screened and treated for SAB while hospitalized. Using multivariable regression analysis, stratification of IE risk were derived and then applied to the validation group to verify the diagnostic value of TTE. Statistical analysis showed that likelihood of developing IE was associated with four high risk-associated factors and the presence of any one criterion demonstrated 97% sensitivity (CI95: 87%-100%), 99% negative predictive value (CI95: 96%-100%) with a negative likelihood ratio of 0.05 (CI95: 0.007-0.35)for IE. The four high risk criteria were:  indeterminate or positive TTE (p < 0.001),  community-acquired bacteremia (p = 0.034),  IV drug use (p < 0.001), and  high-risk cardiac condition (p < 0.004).
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