To describe the epidemiology of nosocomial infections in combined medical-surgical (MS) intensive care units (ICUs) participating in the National Nosocomial Infection Surveillance (NNIS) System.

Analysis of surveillance data on 498,998 patients with 1,554,070 patient-days, collected between 1992 and 1998 from 205 MS ICUs following the NNIS Intensive Care Unit protocol, representing 152 participating NNIS hospitals in the United States.

Infections at three major sites represented 68% of all reported infections (nosocomial pneumonia, 31%; urinary tract infections (UTIs), 23%; and primary bloodstream infections (BSIs), 14%: 83% of episodes of nosocomial pneumonia were associated with mechanical ventilation, 97% of UTIs occurred in catheterized patients, and 87% of primary BSIs in patients with a central line. In patients with primary BSIs, coagulase-negative staphylococci (39%) were the most common pathogens reported; Staphylococcus aureus (12%) was as frequently reported as enterococci (11%). Coagulase-negative staphylococcal BSIs were increasingly reported over the 6 years, but no increase was seen in candidemia or enterococcal bacteremia. In patients with pneumonia, S aureus (17%) was the most frequently reported isolate. Of reported isolates, 59% were gram-negative bacilli. In patients with UTIs, Escherichia coli (19%) was the most frequently reported isolate. Of reported isolates, 31% were fungi. In patients with surgical-site infections, Enterococcus (17%) was the single most frequently reported pathogen. Device-associated nosocomial infection rates for BSIs, pneumonia, and UTIs did not correlate with length of ICU stay, hospital bed size, number of beds in die ICU, or season. Combined MS ICUs in major teaching hospitals had higher device-associated infection rates compared to all other hospitals with combined medical-surgical units.

Nosocomial infections in MS ICUs at the most frequent infection sites (bloodstream, urinary, and respiratory tract) almost always were associated with use of an invasive device. Device-associated infection rates were die best available comparative rates between combined MS ICUs, but the distribution of device-associated rates should be stratified by a hospital's major teaching affiliation status.