Changing patterns of infections and antimicrobial susceptibilities.

Nosocomial bloodstream infections across the United States and in Europe are increasingly attributable to gram-positive species--a trend that represents a reversal of the gram-negative predominance of the previous decades. Data from Memorial Sloan-Kettering Cancer Center and elsewhere show that patients with hematologic malignancies or patients who are immunocompromised because of anticancer treatments are experiencing this shift in microbial spectrum. Most common among gram-positive species are coagulase-negative Staphylococci. Antimicrobial resistance continues to increase, which makes treatment more difficult for infections caused by some species, especially vancomycin-resistant enterococcal species. The underlying causes of changes in microbial spectrum and drug-resistance patterns are incompletely understood, but it is clear that antibiotic exposure exerts a significant selective pressure on pathogens, resulting in partial or complete resistance. New drugs or drug combinations will be necessary to treat drug-resistant infections in cancer patients.