Number of persons needed To analyze a dozen potential risk factors must be provided about 110 events. With an acquisition rate estimated at 20%, 570 subjects analyzed are needed. The inclusion of 750 subjects, of which 5% will probably be excluded as carriers of MRE before the trip and 20% will be lost sight of, will achieve this goal of 570 subjects analyzed. The inclusion of 250 subjects (190 analyzed) in each of three geographical areas (Asia, Latin America, Sub-Saharan Africa), will estimate the rate of acquisition zone with an accuracy of about 5%.