To assess the influence of nosocomial infection on length of stay in the intensive care unit (ICU) and to determine the relative effect of other factors on extra length of hospitalization associated with nosocomial infection.

Prospective cohort multicenter study in the context of the ENVIN-UCI project.

Medical or surgical ICUs of 49 different hospitals in Spain.

All consecutive patients (N = 6,593) admitted to ICUs of the participating hospitals who stayed for more than 24 hours during a 3-month period (from January 15 to April 15, 1996) were included. Length of ICU stay was compared between patients with and without nosocomial infections.

Uninfected patients (N = 5,868) had a median stay in the ICU of 3 days, whereas the median for infected patients (N = 725) was 17 days (P < .001). The median for infected patients with one episode of nosocomial infection was 13 days. The greatest length of stay (40 days) was among patients admitted to the ICU because of medical diseases, with an infection acquired before admission to the ICU, and with the largest number of nosocomial infection episodes. In extended stays, nosocomial infection was significantly associated with length of hospitalization (day 21; odds ratio, 22.38; 95% confidence interval, 16.6 to 30.4), whereas an effect of variables related to severity of illness on admission (Acute Physiology and Chronic Health Evaluation II score, urgent surgery, and infection prior to ICU admission) was not found.

The presence of nosocomial infection and the number of infection episodes were the variables with the strongest association with prolonged hospital stay among ICU patients.