Nosocomial bloodstream infections: organisms, risk factors, and implications.

In the last 30 years, the frequency, etiology, and epidemiology of bloodstream infections (BSIs) have changed with the evolution of medical care, particularly among the increasing number of hospitalized patients who require intensive care. Although gram-negative bacilli were the predominant nosocomial pathogens in the 1970s, gram-positive cocci have emerged as a more frequent cause of nosocomial BSIs during the 1980s and 1990s. Many gram-positive cocci associated with nosocomial BSIs are now resistant to commonly used antibiotics. Currently, the 3 most common causes of nosocomial BSIs in the United States are coagulase-negative staphylococci, Staphylococcus aureus, and enterococci. The emergence of vancomycin-resistant staphylococcal infections is of particular concern. In addition, the incidence of methicillin-resistant S. aureus (MRSA) infections appears to be increasing; however, the effect of MRSA infection on mortality in hospitalized patients remains unclear. Therefore, newer, more effective antimicrobial therapies are needed to treat BSIs caused by gram-positive cocci are needed.