Outcomes for complicated intra-abdominal infection are influenced by operation for source control, patient-related factors, and medical management, including antibiotic treatment. We analyzed length of stay (LOS) at 33 hospitals for 2,150 patients discharged between February 2002 and June 2003, who were >18 years, had intra-abdominal infection, and received one of 6 first-line antimicrobials. A regression tree analysis selected important variables, their interactions, and their order of significance in explaining LOS. A linear mixed model evaluated the difference in LOS between treatment groups. Adjusted LOS was calculated by the least squares means from the model and was used to assess treatment differences. Mean LOS analyzed by initial antimicrobial therapy and stratified by diagnosis showed LOS for ampicillin/sulbactam and ertapenem to be significantly shorter from levofloxacin, ceftriaxone, and piperacillin/tazobactam (all P < 0.05). Adjusting for all other factors, the variables associated with severity (e.g., diagnosis, ICU stay, and comorbidities) had the greatest impact on adjusted LOS (all P < 0.001). Our findings indicate ampicillin/sulbactam and ertapenem were associated with shorter hospital stays, which may be explained by unaccounted for underlying severity of infection and/or by surgeons stratifying antimicrobial selection according to severity of illness.
