Changing patterns of blood culture isolates from patients with acute leukemia: a review of twenty years' experience.

During the 20-year period, 1972-1991, 286 episodes of bacteremia occurred in 200 (45%) of 445 patients with acute leukemia in a hematology ward, giving an incidence of 482 episodes per 1,000 hospital admissions. The frequency of bacteremia was almost unchanged throughout the study period. The frequency of gram-negative bacilli decreased significantly, however, from 81% of all the isolates for the first half of the study period to 50% for the latter half. Despite the common use of ceftazidime and imipenem during the last 5-year period, Pseudomonas aeruginosa increased in frequency to be the most frequent organism. This was opposite to the decreased frequencies of Escherichia coli, Klebsiella pneumoniae and Enterobacter cloacae. The isolates of P. aeruginosa obtained during this period, all of which proved sensitive to ceftazidime and/or imipenem, were almost equally distributed among five serogroups, although a temporal preponderance of a limited number of serogroups was observed during the preceding 15-year period. On the other hand, the frequency of gram-positive cocci increased from 9% in the first decade to 35% in the latter decade. Staphylococcus epidermidis, Enterococcus species and, to a lesser extent, Staphylococcus aureus were ranked as major pathogens. Among the recent isolates of S. aureus, methicillin-resistant strains virtually replaced methicillin-sensitive ones. Therefore, until more effective means for control of P. aeruginosa bacteremia in particular become available, the occurrence of this infection will continue to limit the successful treatment of acute leukemia.