From the Journals

Two consecutive negative FUBC results clear S. aureus bacteremia



Additional blood cultures are not needed after two negative follow-up blood culture results in well-appearing patients with Staphylococcus aureus bacteremia, reported Caitlin Cardenas-Comfort, MD, of the section of pediatric infectious diseases at Baylor College of Medicine, Houston, and colleagues.

CDC/Janice Haney Carr

In a retrospective cohort study of 122 pediatric patients with documented Staphylococcus aureus bacteremia (SAB) that were hospitalized at one of three hospitals in the Texas Children’s Hospital network in Houston, Dr. Cardenas-Comfort and colleagues sought to determine whether specific recommendations can be made on the number of follow-up blood cultures (FUBC) needed to document clearance of SAB. Patients included in the study were under 18 years of age and had confirmed diagnosis of SAB between Jan. 1, and Dec. 31, 2018.

Most cases of bacteremia resolve in under 48 hours

In the majority of cases, patients had bacteremia for less than 48 hours and few to no complications. Only 16% of patients experienced bacteremia lasting 3 or more days, and they had either central line-associated bloodstream infection, endocarditis, or osteomyelitis. In such cases, “patients with endovascular and closed-space infections are at an increased risk of persistent bacteremia,” warranting more conservative monitoring and follow-up, cautioned the researchers.

Although Dr. Cardenas-Comfort and colleagues did note an association between the duration of bacteremia and a diagnosis of infectious disease, increased risk for persistent SAB did not appear to be tied to an underlying medical condition, including immunosuppression.

Fewer than 5% of patients with SAB had intermittent positive cultures and fewer than 1% had repeat positive cultures following two negative FUBC results. For those patients with intermittent positive cultures, the risk of being diagnosed with endocarditis or osteomyelitis is more than double. The authors suggested that “source control could be a critical variable” increasing the risk for intermittent positive cultures, noting that surgical debridement occurred more than 24 hours following initial blood draw for every patient in the osteomyelitis group. In contrast, of those who had consistently negative FUBC results, only 2 of 33 (6%) had debridement in the same period, and only 6 of 33 (18%) required more than one debridement.

Children are less likely to have intermittent positive cultures

Dr. Cardenas-Comfort and colleagues also observed that intermittent positive cultures may appear less frequently in children than adults, consistent with a recent study of adults in which intermittent cultures were found in 13% of 1.071 SAB cases. In just 4% of the cases in that study, more than 2 days of negative blood cultures preceded a repeat positive culture.

The researchers noted several study limitations in their own research. Because more than half (61%) of patients had two or less FUBCs collected, and 21% one or less, they acknowledged that their conclusions are based on the presumption that the 61% of patients would not have any further positive cultures if they had been drawn. Relying on provider documentation also suggested that cases of bacteremia without an identified source also likely were overrepresented. The retrospective nature of the study only allowed for limited collection of standardized follow-up metrics with the limited patient sample available. Patient characteristics also may have affected the quality of study results because a large number of patients had underlying medical conditions or were premature infants.


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