COAGULASE-NEGATIVE STAPHYLOCOCCI IN MULTIPLE BLOOD CULTURES - STRAIN RELATEDNESS AND DETERMINANTS OF SAME-STRAIN BACTEREMIA

The frequency of strain relatedness was determined among randomly sele cted patients with coagulase-negative staphylococcal infections as det ermined in multiple blood cultures by plasmid typing, determination of species, and antibiotyping. Strain relatedness was demonstrated in 21 of 47 episodes of bacteremia (44.7%) among 34 patients, with a simila r percentage among patients with two or one positive blood culture in 24 h (14 of 30 [46.7%] versus 7 of 17 [41.2%], respectively). Same str ain bacteremia was more frequent in cases of infection among patients with a corresponding fever (15 of 21 [71.4%]), among patients infected with organisms from an identifiable source (7 of 9 [77.8%]) and with non-Staphylococcus epidermidis species (9 of 11 [81.8%]), and among pa tients with nosocomially acquired infections (18 of 36 [50%]), Compari ng episodes with or without strain relatedness, no difference was note d in the time to growth (2.1 +/- 1.4 versus 1.9 +/- 0.9 days, respecti vely), in bacterial growth in two culture bottles (5 of 14 [35.7%] ver sus 8 of 24 [33.3%], respectively), and in the presence of additional negative blood cultures (9 of 21 [42.9%] versus 11 of 26 [42.3%], resp ectively). The antibiotypes of all related strains and 7 of 44 (15.9%) unrelated pairs were identical. These findings demonstrate that coagu lase-negative staphylococci from multiple blood cultures are frequentl y unrelated, suggesting a high prevalence of contamination, In the abs ence of precise measures for demonstrating strain relatedness, the com bination of a clinical assessment with antibiotype determination appea rs to be a suitable alternative.