By Stan Deresinski, MD, FACP, FIDSA

Clinical Professor of Medicine, Stanford University

SYNOPSIS: A single set of blood cultures may be inadequate to document clearance of Staphylococcus aureus bacteremia in some patients.

SOURCE: Go JRU, Baddour LM, Lahr B, et al. The skip phenomenon in Staphylococcus aureus bacteremia: Clinical associations. Abstract 9. IDWeek 2021.

Follow-up blood cultures are recommended for documentation of clearance of Staphylococcus aureus bacteremia. For methicillin-resistant S. aureus (MRSA) bacteremia, the 2011 Infectious Diseases Society of America (IDSA) guideline states that, “Additional blood cultures 2-4 days after initial positive cultures and as needed thereafter are recommended to document clearance of bacteremia.”1 The presence of negative blood cultures performed on specimens obtained two to four days after the initial set are among the requirements for considering the bacteremia to be uncomplicated.

However, repeating follow-up blood cultures only once appears to be insufficient. Fiala and colleagues at the Mayo Clinic reported in 2019 that fluctuating blood culture results a skip phenomenon was identified in 29 (4%) of 757 cases of S. aureus bacteremia for whom follow-up cultures were obtained.2 They distinguished this from breakthrough bacteremia, which they indicate refers to continuous or new-onset bacteremia while receiving appropriate antibiotics but does not require documentation of initial clearance of bacteria from the bloodstream. This phenomenon also had been reported by others.

A Mayo group now reports identifying the skip phenomenon in 25 (5.1%) of 495 patients, with significantly increased risks in injection drug users, patients with automatic implantable cardiac defibrillators, and those with community onset of infection. The median duration and grade of bacteremia, frequency of complicated bacteremia, and endocarditis all were greater in those with the skip phenomenon.


These observations indicate that to demonstrate clearance of S. aureus bacteremia, reliance on a single set of blood cultures on a single day clearly is insufficient. It can be speculated that cases considered to represent relapse of bacteremia are, in fact, examples of persistent bacteremia unless sufficient negative cultures have been documented. However, the interval between repeat cultures and the number required to reliably detect the skip phenomenon are unclear, but it may be necessary to perform the cultures on multiple days. 


  1. Liu C, Bayer A, Cosgrove SE, et al. Clinical practice guidelines by the Infectious Diseases Society of America for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children: Executive summary. Clin Infect Dis 2011;52:285-292.
  2. Fiala J, Palraj BR, Sohail MR, et al. Is a single set of negative blood cultures sufficient to ensure clearance of bloodstream infection in patients with Staphylococcus aureus bacteremia? The skip phenomenon. Infection 2019;47:1047-1053.