MORTALITY-RATE AND MAGNITUDE OF STAPHYLOCOCCUS-AUREUS BACTEREMIA AS ASSESSED BY A SEMIQUANTITATIVE BLOOD CULTURE SYSTEM

A 4-year retrospective study ascertained the relation between the magn itude of Staphylococcus aureus bacteremia and mortality. 253 episodes of S. aureus bacteremia diagnosed in a Danish regional Department of C linical Microbiology were included. Blood cultures were routinely done by inoculation of aseptically drawn blood into multiple tubes of bact eriological media. The rate of positive tubes was assumed to distingui sh high- from low-grade bacteremia without providing an absolute count of colony forming units. The median number of tubes inoculated was 18 (range 6-48) with approximately 0.5-1 ml of blood per tube. The rate of positive tubes was related neither to the source of infection, i.e. whether the S. aureus infection was nosocomially or community-acquire d, nor to the portal of entry. However, mortality increased,vith incre asing rate: it was 18% for rates <0.30, 23% for 0.30-0.69, 30% for 0.7 0-0.99, and 37% for a rate of 1.0. Thus, for S. aureus infections the magnitude of bacteremia seems to be a prognostic factor with possible bearings on clinical and therapeutic decisions.