An outbreak of imipenem-resistant Acinetobacter baumannii in critically ill surgical patients

OBJECTIVE: To describe an outbreak of imipenem-resistant Acinetobacter baum annii (IR-Ab) and the measures for its control, and to investigate risk fac tors for IR-Ab acquisition. DESIGN: An observational and a case-control study. SETTING: A surgical intensive care unit (ICU) in a university tertiary care hospital. METHODS: After admission to the ICU of an IR-Ab-positive patient, patients were prospectively screened for IR-AI, carriage upon admission and then onc e a week. Environmental cleaning and barrier safety measures were used for IR-Ab carriers. A case-control study was performed to identify factors asso ciated with hi-Ah acquisition. Cases were patients who acquired IR-Ab. Cont rols were patients who were hospitalized in the ICU at the same time as cas es and were exposed to IR-Ab for a similar duration as cases. The following variables were investigated as potential risk factors: baseline characteri stics, scores for severity of illness and therapeutic intervention, presenc e and duration of invasive procedures, and antimicrobial administration. RESULTS: Beginning in May 1996, the outbreak involved 17 patients over 9 mo nths, of whom 12 acquired TR-Ab (cases), 4 had IR-Ab isolates on admission to the ICU, and 1 could not be classified. Genotypic analysis identified tw o different IR-Ab isolates, responsible for three clusters. Ten of the 12 n osocomial cases developed infection. Control measures included reinforcemen t of barrier safety measures, limitation of the number of admissions, and t horough environmental cleaning. No new case was identified after January 19 97. Eleven of the 12 cases could be compared to 19 controls. After adjustme nt for severity of illness, a high individual therapeutic intervention scor e appeared to be a risk factor for IR-Ab acquisition. CONCLUSION: The outbreak ended after strict application of control measures . Our results suggest that high work load contributes to IR-Ab acquisition (Infect Control Hasp Epidemiol 2001;22:35-40).