Staphylococcus aureus bacteremia in immunosuppressed patients: a multicenter, retrospective cohort study
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Staphylococcus aureus bacteremia (SAB) causes significant morbidity and mortality. We assessed the disease severity and clinical outcomes of SAB in patients with pre-existing immunosuppression, compared with immunocompetent patients. A retrospective cohort investigation studied consecutive patients with SAB hospitalized across six hospitals in Toronto, Canada from 2007 to 2010. Patients were divided into immunosuppressed (IS) and immunocompetent (IC) cohorts; the IS cohort was subdivided into presence of one and two or more immunosuppressive conditions. Clinical parameters were compared between cohorts and between IS subgroups. A competing risk model compared in-hospital mortality and time to discharge. A total of 907 patients were included, 716 (79%) were IC and 191 (21%) were IS. Within the IS cohort, 111 (58%) had one immunosuppressive condition and 80 (42%) had two or more conditions. The overall in-hospital mortality was 29%, with no differences between groups (IS 32%, IC 28%, p = 0.4211). There were no differences in in-hospital mortality (sub-distribution hazard ratio [sHR] 1.17, 95% confidence interval [CI] 0.88–1.56, p = 0.2827) or time to discharge (sHR 0.94, 95% CI 0.78–1.15, p = 0.5570). Independent mortality predictors for both cohorts included hypotension at 72 h (IS: p < 0.0001, IC: p < 0.0001) and early embolic stroke (IS: p < 0.0001, IC: p = 0.0272). Congestive heart failure was a mortality predictor in the IS cohort (p = 0.0089). Fever within 24 h (p = 0.0092) and early skin and soft tissue infections (p < 0.0001) were survival predictors in the IS cohort. SAB causes significant mortality regardless of pre-existing immune status, but immunosuppressed patients do not have an elevated risk of mortality relative to immunocompetent patients.
KeywordsChronic Kidney Disease Acute Kidney Injury Infective Endocarditis Positive Blood Culture Gray Model
This project was performed in collaboration with the Toronto Antimicrobial Stewardship Corridor (TASC). We are indebted to Pamilla Cheema, Bin Chen, Karol Sitarski, Bruce Tugwood, Bonnie Chi Thieu, Mei Shi, and Rochelle Liem for their assistance with the data collection and verification.
Compliance with ethical standards
This study was carried out as part of our routine work. The Sinai Health System-University Health Network Antimicrobial Stewardship Program was supported by an unrestricted educational grant from Pfizer Canada from 2010 to 2012, which partially supported the salary of a research coordinator (M. Steinberg). A Sinai Health System Department of Medicine Summer Studentship Award funded A. Bai. A. Morris receives partial salary support for his antimicrobial stewardship activities from Sinai Health System and University Health Network. A CIHR/CPSI Chair in Patient Safety and Continuity of Care supports C. Bell.
Conflict of interest
No authors had any conflicts of interest to declare.
Research Ethics Board approval was obtained at each of the participating sites.
All Research Ethics Boards approved waiver of consent due to the retrospective nature of the study.
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