Methodology Adults consultant in a vaccination center of one of the six investigator wards, prior to a holiday in the tropics are approached by an investigator to participate in the study. The volunteers will send by mail to the laboratory a stool sample in the weeks prior to departure and another within 72 hours after return from which will be investigated and quantified the MRE. Data will be collected by the investigator and then by a self-administered questionnaire to establish risk factors for acquiring MRE during the stay. If positive, follow-up (1, 2, 3, 6, 12 months) will be undertaken to measure the duration of carriage and the dynamics of the concentration of MRE in the stool after the return. The occurrence of urinary tract infections MRE will be recorded. Subjects will be indemnified according to the number of samples sent.