Patient-to-Patient Transmission of Acinetobacter baumannii Gastrointestinal Colonization in the Intensive Care Unit.

Acinetobacter baumannii is an important nosocomial pathogen. The objective of this study was to determine the proportion of A. baumannii infections due to patient-to-patient transmission by analyzing the molecular epidemiology of patients who acquired A. baumannii, using perianal surveillance cultures in a large 2-year intensive care unit (ICU) population. The design was a prospective cohort study. Patients who were admitted to the medical and surgical intensive care units at the University of Maryland Medical Center from 2011 to 2013 underwent admission, weekly, and discharge perianal culture collection. Using multilocus sequence typing (MLST) with subsequent pulsed-field gel electrophoresis (PFGE) for increased discrimination, combined with hospital overlap, the number of patients that acquired A. baumannii due to patient-to-patient transmission was determined. Our cohort consisted of 3,452 patients. In total, 196 cohort patients were colonized with A. baumannii; 130 patients were positive at ICU admission, and 66 patients acquired A. baumannii during their stay. Among the 196 A. baumannii patient isolates, there were 91 unique MLST types. Among the 66 patients who acquired A. baumannii, 31 (50%) were considered genetically related by MLST and/or PFGE type, and 11 (17%) were considered patient-to-patient transmission by genetic relatedness and overlapping hospital stay. Our data show that, of those cases of A. baumannii acquisition, at least 17% were cases of patient-to-patient transmission.