Outbreak caused by Escherichia coli in Chalco, Mexico

Objective. To identify the etiologic agent responsible for a disease outbreak following an overflow of sewage water in Valle de Chalco, Mexico. Material and Methods. A retrospective cross-sectional study was carried out. Rectal samples were collected from the population of Chalco valley, who suffered from diarrhea and vomiting during a natural disaster that took place on May 31, 2000. The Instituto cle Diagnostico y Referencia Epidemiologicos (Epidemic Reference and Diagnosis Institute, InDRE, Ministry of Health), received 1521 rectal swab samples from diarrhea cases, to test for E coli strains. Statistical analysis was performed to find a difference of proportions between cases and non-cases (chi-squared test). ETEC, EIEC, EPEC and EHEC pathogenic E coli groups were hybridized by colony blot. Results. Strains isolated were ETEC (62.2%), EIEC (0.84%), EPEC (0.84%), and EHEC non-O157:H7 (0.08%); there was no hybridization in 36.02% of E coli strains. Other isolated microorganisms were Salmonella spp (0.45%) and Shigella spp (0.06%). Conclusions. Enterotoxigenic E coli was the most likely etiologic agent. Sanitary control strategies should be targeted to preventing outbreaks caused by this pathogenic agent. The English version of this paper is available at: http://www.insp.mx/salud/index.html.