Colonization with Multidrug-Resistant Gram-Negative Bacteria: Prolonged Duration and Frequent Cocolonization

Background. The characteristics of colonization with multidrug-resistant gram-negative bacteria (MDRGNB) in the gastrointestinal tract have not been well defined. Characterizing the duration of colonization, clearance of colonization, and frequency of cocolonization would provide important information for the development of interventions targeting the prevention of MDRGNB spread. Methods. From 31 October 2006 through 22 October 2007, serial rectal cultures were obtained every 3–4 weeks from residents of a long-term care facility. Clearance of colonization was defined as ⩾2 consecutive cultures from which MDRGNB were not recovered. Factors associated with clearance of colonization were analyzed using time-to-event methods. Results. Thirty-three patients colonized with 57 MDRGNB isolates were followed up for a median of 211 days (range, 63–356 days). Twenty (61%) of the patients were colonized with ⩾1 different MDRGNB species (median, 2 strains; range, 1–4 strains). The median duration of MDRGNB colonization was 144 days (range, 41–349 days). Clearance of colonization with all MDRGNB strains occurred in 3 patients (9%). Clearance of MDRGNB colonization, calculated by colonizing strain, occurred in 22 (39%) of 57 MDRGNB colonization episodes, with a rate of colonization clearance of 2.6 episodes per 1000 days. Clearance of multidrug-resistant Proteus mirabilis colonization occurred in 1 (6.7%) of 15 episodes, compared with clearance of 21 (50%) of 42 colonization episodes due to other MDRGNB species (hazard ratio, 0.1; 95% confidence interval, 0.01–0.78; P=.03). Conclusions. Patient colonization with MDRGNB is prolonged, and a substantial proportion of patients are colonized with multiple MDRGNB species. Multidrug-resistant P. mirabilis may have a survival advantage in the gastrointestinal tract, compared with other MDRGNB species.