Seasonality of Diarrheagenic Escherichia coli Pathotypes in the US Students Acquiring Diarrhea in Mexico

Objective. A study was undertaken to determine if ambient temperature and rainfall have an impact on the acquisition of TD due to different diarrheagenic E coli pathotypes in Mexico. Methods. We conducted a cohort study of the US adult students traveling to Cuernavaca, Mexico, who were followed during their stay and provided a stool sample with the onset of TD. The presence of E coli was analyzed by a direct fecal multiplex polymerase chain reaction for common E coli pathotypes including enterotoxigenic, enteropathogenic, enteroinvasive, shiga toxin-producing, and enteroaggregative E coli (ETEC, EPEC, EIEC, STEC, and EAEC respectively). The presence of pathotypes was correlated with daily rainfall, average, maximum, and minimum temperatures. Results. A total of 515 adults were enrolled from January 2006 to February 2007. The weekly attack rate of TD for newly arrived travelers was lower in the winter months (range 6.8%-16.3%) than in summer months (range 11.5%-25%; p = 0.05). The rate of ETEC infection increased by 7% for each degree centigrade increase in weekly ambient temperature (p = 0.003). In contrast, EPEC and EAEC were identified in similar proportions during the winter and summer seasons. Conclusions. Temperature variations in central Mexico influenced the rate of ETEC but not EAEC-associated diarrhea in the US visitors. This epidemiological finding could influence seasonal recommendations for the use of ETEC vaccines in Mexico.