Strain-relatedness of methicillin-resistant Staphylococcus aureus isolates recovered from patients with repeated infection

Abstract

Invasive disease following methicillin-resistant Staphylococcus aureus (MRSA) detection is common, regardless of whether initial detection involves colonization or infection. We assessed the genetic relatedness of isolates obtained > or =2 weeks apart representing either repeated infections or colonization-infection sets to determine if infections are likely to be caused by previously harbored strains. We found that MRSA infection following initial colonization or infection is caused by the same strain in most cases, suggesting that a single successful attempt at decolonization may prevent the majority of later infection.

Figure 1

Dendrogram demonstrating the broad diversity of methicillin-resistant Staphylococcus aureus (MRSA) strains across patients at a single participating institution. The dendrogram is based on PFGE of MRSA isolates from discrete events. Seventeen patients are represented, each identified by a number on the right side of the figure. Fourteen patients had multiple discrete bacteremic events, and 3 patients had bacteremia following surveillance isolates. Letter designations within a given number refer to isolates from the same patient. In this example institution, no 2 patients have identical isolates based on PFGE. Identical strain types may be slightly offset in pattern as a result of small differences in lane alignment or gel characteristics when grouping strains for dendrogram analysis.