Nosocomial infection remains a significant consequence of hospitalization. Estimates are that from 3% to 5% of patients leave the hospital having acquired infection, depending on case mix, hospital size, and multiple other factors. Examination of the microbial etiology of these infections provides important information in day-to-day decision making in individual hospitals regarding potential outbreaks, unusual pathogens, antimicrobial resistance, and local trends in the etiology of infection. It is also useful periodically to examine trends in the etiology of infection over more prolonged time periods to detect shifts in the cause of infection.