PID10: EFFECTS OF LINEZOLID ON HOSPITAL LENGTH OF STAY IN METHICILLIN-RESISTANT STAPHYLOCOCCUS INFECTIONS ESTIMATED FROM MULTIVARIATE SURVIVAL ANALYSIS

OBJECTIVES: To estimate differences in adjusted hospital length of stay (LOS) between linezolid and vancomycin using multivariate survival analysis. Linezolid's bioequivalent IV and oral formulations may enable earlier hospital discharge compared to vancomycin treatment. METHODS: 460 hospitalized patients with suspected/confirmed methicillin-resistant Staphylococcus infections were treated with either linezolid (LZD) or vancomycin (VAN) in a randomized controlled trial. Covariate imbalances between treatment groups were tested using t-tests and chi-square tests. Multivariate Cox proportional hazards and several parametric models for LOS were tested for best fit using the Akaike Information Criteria and log-likelihood ratio statistics. The Cox proportional hazards assumption was rejected (p < .05); log-logistic survival models fit best. The log-logistic estimates are used to create two alternative adjusted survivorship functions, one based on individual corrections to LOS (Individual correction), and the other based on means of the predicted survivorship function for each individual (Mean survivorship). Adjusted LOS at quartiles of % discharged for each function was compared with unadjusted LOS using Kaplan-Meier method. RESULTS: Hospital unit type at randomization and number of comorbidities both differed significantly between groups and significantly affected LOS. With covariate controls in the log-logistic model, linezolid treatment significantly reduced LOS (p = .04). Adjusted/unadjusted LOS at quartiles of % discharged were: CONCLUSIONS: When adjusted for covariate differences, median LOS for linezolid patients was at least 2 days shorter than for vancomycin patients. Other differences in the LOS distribution are evident and may be important to decision-makers but off-median estimates may be sensitive to the adjustment method used. Methodologic considerations are explored further. % discharged Adjusted LOS (days) Unadjusted LOS   Individual correction Mean survivorship               Kaplan-Meier   LZD VAN LZD VAN LZD VAN 25 6 10 6 9 6 8 50 (median) 14 16 13 16 14 15 75 26 28 28 29 29 29