Trends in antimicrobial resistance in health care-associated pathogens and effect on treatment.

Antimicrobial resistance in health care-associated pathogens is a growing concern for health care and for public health. A recent shift in the epidemiological profile of methicillin-resistant Staphylococcus aureus has resulted not only in health care-associated infections but now, also, in community-associated infections. Reports have described S. aureus exhibiting decreased susceptibility and, even, resistance to vancomycin. The rate of vancomycin resistance among enterococci may be leveling; however, vancomycin resistance in Enterococcus faecium has already achieved high levels. Multidrug resistance in Pseudomonas aeruginosa is increasing, and carbapenem-resistant Klebsiella strains are emerging. Acinetobacter species cause a minority of health care-associated pneumonias due to gram-negative organisms, but a growing proportion is resistant to carbapenems and third-generation cephalosporins. Recent increases in the frequency and severity of Clostridium difficile-associated illness are associated with the emergence of a hypervirulent C. difficile strain with increased resistance to the fluoroquinolones. The presence of these and other resistant organisms in health care facilities limits the number of effective antimicrobials available for treatment.