Daily food histories for one month were obtained in summer, 1975, from students attending a Mexican university to determine the influence of food consumption on the development and etiology of diarrhea. In newly-arrived students from the U.S. who ate half or more of their meals in the school cafeteria and public restaurants there were significant increases in diarrhea (p less than 0.005); shigella infection (p less than 0.05) and toxigenic E. coli infection (p less than 0.025) compared to the students eating a comparable number of meals in private homes. In the summer U.S. students there was also an association of diarrhea and eating from street vendors (p less than 0.05). In full-time U.S. students who had lived in Mexico a year or longer as well as in Latin American students a relationship between location of meals and occurrence of enteric disease was not apparent. High numbers of enteric bacteria were recovered from food from the school's cafeteria, public restaurants, street vendors and small grocery stores. Shigella were isolated from cooked and uncooked hamburger patties from the school cafeteria. Four shigella carriers were found among kitchen personnel at the school. This study demonstrates that food serves as a major vehicle through which travelers' diarrhea occurs.

A clinic was established at Universidad de las Americas, Cholula, Puebla, Mexico for the study of acute diarrhea rates in newly-arrived students and full-time students. Diarrhea occurred in 22 of 55 newlly-arrived U.S. summer students (40%), compared to 28 of 142 U.S. full-time students (20%), 4 of 29 Venezuelan summer and full-time students (14%) and 7 of 66 Mexican full-time students (11%) (the differences were significant, p less than 0.005). Recurrent episodes of diarrhea during the month of study occurred in 15% of U.S. summer students, 4% of U.S. full-time students, and were non-existent in students from Latin America. As well as the 61 students with diarrhea enrolled in the incidence study, all students who developed diarrhea at the univeristy were encouraged to visit the clinic. This gave a total population of 130 cases of diarrhea. The illness that developed in students form the U.S. varied widely, but it typically consisted of seven to 13 unformed stools during the first 48 hours of illness, with illness persiting three to five days. Illness tended to be more severe in the U.S. students. Fifty per cent of the U.S. students with diarrhea had "severe" illness (greater than or equal to 10 unformed stools in first 48 hours) compared to 23% of the Latin Americans. This study indicates that the agents responsible for diarrhea in Latin America are widespread and that resistance to infection develops after prolonged or repeated exposure.