NEW ORLEANS — For older men being treated for Staphylococcus aureus bacteremia who have received immunosuppressive agents, a single negative blood culture may be insufficient to demonstrate clearance, based on findings presented here at IDWeek 2016.
Justin Fiala, MD, of the internal medicine department at the Mayo Clinic, described a period of fluctuating blood culture positivity in which there is a recurrence of S. aureus bacteremia infection following a negative blood culture, despite the patients receiving appropriate antibiotic therapy. This discrete finding, which he termed the “skip phenomenon,” had not previously been described in the literature, he said.
Fiala and colleagues retrospectively reviewed a cohort of adult inpatients with 3 or more days of S. aureus bacteremia at the Mayo Clinic from a previous trial conducted between July 2006 and June 2011. Blood culture data were reviewed for all patients, and the skip phenomenon was defined as 1 or more days of negative blood cultures following documented infection and before a recurrence of the infection. Patients had to be receiving appropriate ongoing antibiotic therapy and had to have the same bacterial susceptibility profile both before and after the skip period.
Of the 726 patients studied, 29 (4%) were determined to have experienced the skip phenomenon. Of these patients, 90% were men; the median age for all patients was 69.4 years. Researchers attempted to match the duration of bacteremia between the study and control groups, but there was a longer duration in patients who experienced the skip phenomenon: 10 days vs. 8 days.
Researchers noted that 90% of patients in the skip phenomenon group were receiving chronic immunosuppression, compared with 79% in the control group, though this difference was not statistically significant. No significant differences were found between the groups in terms of preexisting conditions, the presence of implanted devices, bacterial susceptibility, treatment regimen or infection site.
Risk factors for the recurrence of S. aureus bacteremia that had been reported previously, such as vancomycin monotherapy, deep-seated infection, community onset and MRSA, were not found to be predictive of the skip phenomenon, Fiala said.
There was a trend toward increased mortality among patients who experienced the skip phenomenon, but this was not statistically significant.
“At the very least, we can say that there is increased morbidity associated with the skip phenomenon,” Fiala said.
Fiala acknowledged the relatively small number of patients identified as having experienced the skip phenomenon and the retrospective nature of the review as limitations of the study. Despite these considerations, there were clinical recommendations that could be drawn from their findings, he said.
“The skip phenomenon does occur in a significant number of patients – approximately 4% of patients with S. aureus bacteremia,” Fiala said. “If we try to think about which patients might this be applicable for — males over 65 years old on chronic immunosuppression … and with a longer duration of index S. aureus bacteremia, it might be worth considering getting serial cultures to show that they have definitively cleared ... because there may be significant morbidity, if not mortality, associated with this.” – by Chris Rosenberg
Fiala J, et al. Abstract 117. Presented at: IDWeek; Oct. 26-30, 2016; New Orleans.
Disclosure: The researchers report no relevant financial disclosures.