Research Article: Characteristics of Staphylococcus aureus Bacteraemia and Predictors of Early and Late Mortality

Date Published: February 2, 2017

Publisher: Public Library of Science

Author(s): Matteo Bassetti, Maddalena Peghin, Enrico Maria Trecarichi, Alessia Carnelutti, Elda Righi, Paola Del Giacomo, Filippo Ansaldi, Cecilia Trucchi, Cristiano Alicino, Roberto Cauda, Assunta Sartor, Teresa Spanu, Claudio Scarparo, Mario Tumbarello, Karsten Becker.


We aimed to describe the characteristics of patients with Staphylococcus aureus bacteremia and to evaluate the risk factors associated with early (7-day) and late (30-day) mortality. We performed an observational study including all consecutive episodes of Staphylococcus aureus bacteremia diagnosed at two Italian university hospitals during 2010–2014. A total of 337 patients were included. Mean age was 69 years (range, 57–78) and 65% were males. Methicillin-resistant S. aureus (MRSA) was identified in 132/337 (39%)cases. Overall 7- and 30-day mortality were 13% and 26%, respectively. Early mortality was associated with increased Charlson scores (OR 1.3, 95% CI 1.1–1.5), MRSA bacteremia (OR 3.2, 95% CI 1.4–8.1), presentation with septic shock (OR 13.5, 95% CI 5.4–36.4), and occurrence of endocarditis (OR 4.5, 95%CI 1.4–14.6). Similar risk factors were identified for late mortality, including increased Charlson scores (OR 1.2, 95% CI 1.1–1.4), MRSA bacteremia (OR 2.1, 95% CI 1.2–3.9), presentation with septic shock (OR 4, 95%CI 1.7–9.7), occurrence of endocarditis (OR 3.8, 95% CI 1.4–10.2) as well as Child C cirrhosis (OR 3.9, 95% CI 1.1–14.4) and primary bacteremia (OR 2.5, 95%CI 1.3–5). Infectious disease consultation resulted in better outcomes both at 7 (OR 0.1, 95% CI 0.05–0.4) and at 30 days (OR 0.4, 95% CI 0.2–0.7). In conclusion, our study highlighted high rates of MRSA infection in nosocomial Staphylococcus aureus bacteremia. Multiple comorbidities, disease severity and methicillin-resistance are key factors for early and late mortality in this group. In patients with Staphylococcus aureus bacteremia, infectious disease consultation remains a valuable tool to improve clinical outcome.

Partial Text

The distribution of methicillin-sensitive (MSSA) and methicillin-resistant S. aureus (MRSA) bacteremia varies substantially by geographical region [1] [2] [3] [4] [5]. Staphylococcus aureus, however, remains a leading cause of community- and healthcare-associated bacteremia worldwide [3] [5]. Despite efforts to reduce its incidence, S. aureus bacteremia (SAB) remains frequent and associated with mortality rates up to 25% [3]. SAB acquisition and outcome are affected by patients’ comorbidities, infection site, and methicillin-resistance [6] [7]. In this patient population, evidence-based bundle interventions demonstrated to have a positive impact in clinical management and outcome [8]. In particular, results from a recent metanalysis suggested that infectious diseases (ID) consultation might improve clinical care and impact hospital survival in patients with SAB [8]. Most of the studies, however, focused on predictors of 30- and 60 day-mortality even if high early (≤ 7 day) mortality rates have been reported among patients with SAB [6] [7] [8] [9] [10, 11] [12].Aim of the study was to describe the epidemiology and clinical characteristics of patients with SAB and assess the prognostic factors for early (7-day) and late (30-day) mortality.

The proportion of MRSA has declined in the United States and in some European countries, including Italy, over the past years, but still remains a concern for public health and a major cause of nosocomial infections [1] [2]. In our study, we observed methicillin-resistance rates of about 40%, slightly higher than 34% reported for Italy by the European Antimicrobial Resistance Surveillance Network in 2014 [1]. In our study, MRSA accounted for most nosocomial and healthcare-associated infections but only for a limited proportion of community-acquired infections, stressing the importance of the clinical setting in defining patient populations at risk for MRSA bacteremia [17] [18]. Previous studies showed higher mortality rates among patients with MRSA bacteremia compared to MSSA, but the results are conflicting [7] [12] [19] [20] [21]. In our study, methicillin resistance was an independent risk factor for both early and late mortality survival. One reason could be represented by higher rates of inadequate treatment associated with MRSA compared to MSSA or by other potential confounding factors (e.g., disease severity, risk factors) associated with MRSA infections [10] [20] [22] [23]. Our study, in particular, showed lower rates of appropriate empiric and definitive therapy in patients with MRSA compared to MSSA infections.

In conclusion, S.aureus bacteremia represents a serious infection, associated with significant both early and late mortality. Methicillin resistance is associated mostly to nosocomial and health-care associated infections and may be a risk factor for mortality in patients with SAB. Clinicians should be aware of the severity of patients with S. aureus bacteremia, and infectious disease consultation should be always considered to improve patients’ outcomes.




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