The objective of the study was to determine if the presence or absence of
virulence factor-positive and -negative enteroaggregative Escherichia coli (EAEC) determined the occurrence of illness or sub-clinical EAEC
infection in travelers from the United States to Mexico. Sixty-five newly arrived college students from the United States submitted weekly stool samples for a four-week period of time. Among EAEC-infected subjects,
diarrhea occurred in those with a defined
virulence factor with the following frequency:
aggA, 5 of 15 (33%); aggR, 3 of 11 (27%); aafA, 3 of 8 (38%); and
aspU, 1 of 6 (17%). Twenty-two of 31 students (71%) had two or more EAEC
infections. After the initial EAEC
infection, only 4 (11%) of 31 students had a subsequent symptomatic EAEC
infection. Our study suggests that clinical illness by EAEC is not explained by presence of a defined EAEC
virulence factors, and we provide suggestive evidence that EAEC
infection protects against future symptomatic
infection.