Is a single set of negative blood cultures sufficient to ensure clearance of bloodstream infection in patients with Staphylococcus aureus bacteremia? The skip phenomenon
The most recent version of the Infectious Diseases Society of America guidelines for the treatment of methicillin-resistant Staphylococcus aureus infections states that a single set of negative blood cultures is sufficient to demonstrate clearance of bacteremia. However, S. aureus might exhibit fluctuating blood culture positivity, labeled as “the skip phenomenon”. Our objectives were to determine the prevalence of the skip phenomenon in a cohort of hospitalized patients with S. aureus bacteremia and to determine the associated clinical variables.
We conducted a nested case–control study, using a previous cohort of 757 adult inpatients between July 2006 and June 2011 with ≥ 3 days of S. aureus bacteremia. Each case of S. aureus bacteremia with the skip phenomenon was matched to 2 to 4 controls based on age, gender, and duration of bacteremia. The association of clinical characteristics with the skip phenomenon was analyzed via conditional logistic regression.
Of the 757 patients in the cohort, 29 (4%) had the skip phenomenon. 26 (90%) patients in the cases group were male. The median age was 69.4 years (interquartile range [IQR] 58.7 to 80.3). Although an attempt to match for the duration of bacteremia was done, there was a statistically longer duration in patients with cases as compared to that in controls (median [IQR], 10 [7–12] days, vs 8 [6–10] days; P = 0.015). Accordingly, duration of bacteremia was adjusted for in regression models. Notably, 26 (90%) patients in the case group were receiving chronic immunosuppressive therapy, as compared to 69 (79%) patients in the control group (P = 0.427).
Our findings prompt consideration of a practice chance to obtain serial negative blood cultures to ensure clearance of bacteremia among patients with S. aureus bacteremia.
KeywordsStaphylococcus aureus Bacteremia Blood stream infections Skip phenomenon Blood culture
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Conflict of interest
All authors attest no financial interest or potential conflict of interest specific to the submitted research study. Drs. Rizwan Sohail and Larry Baddour have general disclosures not related to the study: Dr. Sohail reports receiving funds from TYRX Inc. and Medtronic for prior research unrelated to this study administered according to a sponsored research agreement between Mayo Clinic and study sponsor that prospectively defined the scope of the research effort and corresponding budget; and honoraria/consulting fees from Medtronic Inc., Spectranetics, Boston Scientific Corp., and Aziyo Biologics, Inc. Dr. Baddour receives royalty payments for authorship duties from UpToDate, Inc., and consultant payments from Boston Scientific.
Research involving human participants and/or animals
The study did not involve any animals. The research study involved retrospective review of electronic medical records of patient who had agreed to the use of electronic data for research purpose. No intervention was done on human subjects. Patients were not contacted. Institutional review board approved the study and waived requirement of informed consent.