NEW ORLEANS – When Mayo Clinic physicians noticed some patients on appropriate antibiotic treatment for Staphylococcus aureus bacteremia cleared the infection, only to see it recur a few days later, Justin A. Fiala, MD and his colleagues grew curious.
Dr. Fiala, an infectious diseases internist at Mayo Clinic, Rochester, Minn., was intrigued by the possibility of fluctuating blood culture positivity in this subset of bacteremia patients.
“We wanted first to see whether or not this is a real entity and determine the prevalence of this ‘skip pattern,’” Dr. Fiala said at IDWeek 2016, the annual combined meetings of the Infectious Diseases Society of America, the Society for Healthcare Epidemiology of America, the HIV Medicine Association and the Pediatric Infectious Diseases Society. He said identifying predictors and finding any differences in clinical outcomes compared to control S. aureus bacteremia (SAB) patients were additional aims.
Dr. Fiala and his colleagues assessed a hospitalized cohort of 726 adults with SAB at Mayo Clinic between July 2006 and June 2011. Patients with one or more negative blood cultures followed by a positive culture were identified within this group, and compared with 2 to 4 patients matched for age, sex and duration of bacteremia who served as controls.
The investigators found 29 patients – or 4% – of the 726 had this ‘skip pattern’ of infection, clearance, and reinfection. Those with the phenomenon were 90% male and tended to be older, with a mean age of 69 years, compared to the controls. They had index bacteremia about two days longer than controls. The study also revealed a significant difference in mean number of central venous catheters: 2.7 in the skip phenomenon group versus 1.7 in controls.
©CDC/Janice Haney Carr
This scanning electron micrograph (SEM) shows a strain of Staphylococcus aureus bacteria taken from a vancomycin intermediate resistant culture.
Given the predominance of the skip phenomenon in older, immunosuppressed males, “the takeaway … is that serial negative blood cultures may be warranted in these patient groups,” Dr. Fiala said.
The groups did not differ significantly by presence of implants or foreign bodies or by whether SAB was nosocomial or acquired in the community. “We thought it was interesting that 90% had immune suppression, although it was not statistically significant,” Dr. Fiala said.
With no prior reports in the medical literature, the researchers named this clinical entity “skip phenomenon.” Dr. Fiala noted that published studies have assessed recurrence of SAB after completion of antibiotics, but not specifically during treatment.
“We think this is a topic that is quite clinically prevalent and applicable,” Dr. Fiala said. He pointed out that SAB is common, accounting for about 20% of all nosocomial bacteremia cases. SAB also highly virulent with a mortality rate estimated between 20% and 35%. Although the study did not reveal significant mortality differences in the subgroup with skip phenomenon, “we can say there is increased morbidity.”
The most recent IDSA guidelines state that a single set of negative blood cultures is sufficient to demonstrate clearance of SAB, Dr. Fiala said. “Could this be falsely reassuring if Staphylococcus aureus does have a tendency to exhibit this fluctuating pattern?”
The retrospective design of the study and the relatively small number of patients with the skip phenomenon were limitations, the investigators acknowledged. Dr. Fiala had no relevant disclosures.