Association of virulence factor-positive and -negative enteroaggregative Escherichia coli and occurrence of clinical illness in travelers from the United States to Mexico.

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.