The frequency of specific MDR pathogens causing HAP may vary by hospital patient population, exposure to antibiotics, type of ICU patient, and changes over time, emphasizing the need for timely, local surveillance data (3,16,51,65-67). A number of investigators have demonstrated a close association between the prior use of antibiotics and the emergence of subsequent antibiotic resistance both in Gram-negative and Gram-positive bacteria. Other factors promoting antimicrobial resistance include prolonged hospitalization, the presence of invasive devices such as endotracheal tubes and intravascular catheters, possibly due to the formation of biofilms on the surfaces of these devices, residence in long-term treatment facilities, and inadequate infection control practices (63). The emergence of new strains of existing pathogens within the community setting has created additional stressors favoring the entry of resistant microorganisms into the ICU setting. This has most recently been demonstrated by the identification and spread of community-associated MRSA (68,69). However, the prolonged administration of antimicrobial regimens appears to be the most important factor promoting the emergence of antibiotic resistance that is potentially amenable to intervention (70).