Changing etiology of bacteremia in patients with hematological malignancies in Denmark

To ascertain whether the microbiological etiology of bacteremia among patients with hematological malignancies has changed in Denmark, the species distribution of clinically relevant blood culture isolates from the Hematological Department at Rigshospitalet, Copenhagen in 1990 was compared with 2 previous studies (1970-72; 1981-85). In addition, time trends of the etiology of bacteremia among hematological patients in Copenhagen (eastern Denmark) and in Arhus (western Denmark) were compared. In contrast to many other studies, a significant increase in the proportion of Gram-negative aerobes was observed in Copenhagen (from 43% in 1981-85 to 55% in 1990; p < 0.05), whereas in Arhus the proportion of Gram-positive aerobes increased steadily during the 1980s (from 34% to 51%; p < 0.05). In Copenhagen, non-hemolytic streptococci and Xanthomonas maltophilia increased significantly and accounted for 10% (p < 0.01) and 5% (p < 0.05) respectively, of all isolates in 1990, whereas Staphylococcus aureus during the 2 decades studied decreased from 25% to 8% (p < 0.001). In both regions, a decrease was observed in the proportion of Pseudomonas aeruginosa which accounted for only about 5% of all isolates in 1990. No changes were observed in the rates of anaerobes and yeasts. Several factors may contribute to the reported differences in the etiology of bacteremia among hematological patients, e.g. criteria used to assign the clinical significance of the isolate, blood culture system used, practice of using indwelling intravenous catheters, different policies with respect to antimicrobial treatment, and the degree of immunosuppression. A local surveillance of blood culture isolates is mandatory if changes in etiology and resistance development are to be detected.