OBJECTIVE: To compare three methods for assessing the excess nurse work load related to recommended procedures for managing nosocomial infections (NI) due to multiresistant bacteria (MRB): two activity scores, the Omega score and the Projet de Recherche en Nursing (PRN) system, and a specific evaluation based on functional analysis of nursing procedures. SETTING: 10 beds in a medical intensive care unit (MICU). PATIENTS: Patients admitted from November 15, 1995, to June 15, 1996, were included and divided in two groups based on presence of MRB colonization or infection (MRB+ and MRB-groups). METHODS: Data were collected regarding length of stay (LOS) in days; Omega score for the entire stay; PRN score for the entire stay and per day; and time required to perform correctly four nursing procedures related to MRB NI, as evaluated specifically by the nursing staff, using a detailed functional analysis document that described all elementary nursing tasks in chronological order and all material needed to carry out those tasks. RESULTS: The LOS and total Omega and PRN scores were higher in the MRB+ group than in the MRB- group: LOS, 23 +/- 20.6 versus 12 +/- 15.3 days, (P<.001); Omega score, 164 +/- 103.4 versus 123 +/- 93.7 points (P<.001); PRN score, 3,606 +/- 3,187 versus 1,854 +/- 2,356 points (P<.001), respectively. The daily PRN score was also higher in MRB+ group (PRN, 160 +/- 25 vs 146 +/- 34 points in the MRB- group; P<.028). Four nursing procedures made necessary by MRB acquisition were identified: isolation precautions, with two levels according to whether the risk of contamination was mild-moderate or high; bathing the patient with antiseptic solution; bedpan management; and microbiological screening. The functional analysis indicated that the time needed to carry out these four procedures correctly was 245 minutes per patient per day, as compared to 85 minutes according to the PRN system. CONCLUSIONS: Our data confirm that MRB NIs are responsible for an increase in nurse work load, as estimated by LOS, Omega, and PRN scores. However, the daily excess nurse work load related directly to recommended procedures for managing MRB NIs in MICUs is underestimated by these activity scores, as compared to a specific functional analysis of nursing tasks. This may be of importance in evaluating potential links between nurse work load and MRB NIs and in determining the number of nurse hours needed to comply with infection control recommendations.