Determining the Significance of Coagulase-Negative Staphylococci Isolated From Blood Cultures at a Community Hospital A Role for Species and Strain Identification

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Abstract
Objectives:To determine the degree to which species identification or strain relatedness assessment of successive blood culture isolates of coagulase-negative staphylococci (CNS) may improve the clinical diagnosis of bloodstream infection (BSI).Setting:400-bed community hospital.Design:Prospective laboratory survey during which all CNS blood culture isolates obtained between mid-August 1996 and mid-February 1997 (study period) were saved and later identified to the species level; selected isolates were genotyped using pulsed-field gel electrophoresis at the Centers for Disease Control and Prevention (CDC). Retrospective review of medical records of 37 patients with multiple cultures positive for CNS.Results:During the study period, 171 patients had blood cultures positive for CNS; 130 had single positive cultures and 41 had ≥2 positive cultures. Of these 41, 23 (62%) were from patients with signs and symptoms of BSI according to CDC surveillance definitions. Species identification and strain clonality of CNS isolates from patients with ≥2 positives revealed 3 (13%) of the 23 patients did not have a consistent CNS species, and another 3 (13%) did not have a consistent genotype in the ≥2 positive cultures, suggesting that CNS from these patients probably were contaminants. Thus, species identification and strain clonality assessment reduced by 27% the number of patients with BSI diagnosed based on the presence of symptoms and ≥2 positive blood cultures.Conclusions:Routine species identification and selected strain genotyping of CNS may reduce the misinterpretation of probable contaminants among patients with ≥2 positive blood cultures.